tag:theconversation.com,2011:/us/topics/magnetic-fields-1192/articlesMagnetic fields – The Conversation2023-05-15T12:33:56Ztag:theconversation.com,2011:article/2049952023-05-15T12:33:56Z2023-05-15T12:33:56ZQuantum physics proposes a new way to study biology – and the results could revolutionize our understanding of how life works<figure><img src="https://images.theconversation.com/files/525487/original/file-20230510-21-cnx7u8.jpg?ixlib=rb-1.1.0&rect=0%2C0%2C1999%2C1499&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Looking at life at the atomic scale offers a more comprehensive understanding of the macroscopic world.</span> <span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/photo/colorful-model-of-helix-dna-strand-royalty-free-image/157531306">theasis/E+ via Getty Images</a></span></figcaption></figure><p>Imagine using your cellphone to control the activity of your own cells to treat injuries and disease. It sounds like something from the imagination of an overly optimistic science fiction writer. But this may one day be a possibility through the emerging field of quantum biology.</p>
<p>Over the past few decades, scientists have made incredible progress in understanding and manipulating biological systems at increasingly small scales, from <a href="https://theconversation.com/when-researchers-dont-have-the-proteins-they-need-they-can-get-ai-to-hallucinate-new-structures-173209">protein folding</a> to <a href="https://www.genome.gov/genetics-glossary/Genetic-Engineering">genetic engineering</a>. And yet, the extent to which quantum effects influence living systems remains barely understood.</p>
<p>Quantum effects are phenomena that occur between atoms and molecules that can’t be explained by classical physics. It has been known for more than a century that the rules of classical mechanics, like Newton’s laws of motion, <a href="https://iopscience.iop.org/book/mono/978-0-7503-1206-6/chapter/bk978-0-7503-1206-6ch1">break down at atomic scales</a>. Instead, tiny objects behave according to a different set of laws known as <a href="https://www.britannica.com/science/quantum-mechanics-physics">quantum mechanics</a>. </p>
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<figcaption><span class="caption">Quantum mechanics describes the properties of atoms and molecules.</span></figcaption>
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<p>For humans, who can only perceive the macroscopic world, or what’s visible to the naked eye, quantum mechanics can seem counterintuitive and somewhat magical. Things you might not expect happen in the quantum world, like <a href="https://theconversation.com/we-did-a-breakthrough-speed-test-in-quantum-tunnelling-and-heres-why-thats-exciting-113761">electrons “tunneling” through</a> tiny energy barriers and appearing on the other side unscathed, or being in two different places at the same time in a <a href="https://scienceexchange.caltech.edu/topics/quantum-science-explained/quantum-superposition">phenomenon called superposition</a>.</p>
<p>I am trained as a <a href="https://scholar.google.com/citations?user=1aqtpo8AAAAJ&hl=en">quantum engineer</a>. Research in quantum mechanics is usually geared toward technology. However, and somewhat surprisingly, there is increasing evidence that nature – an engineer with billions of years of practice – has learned how to <a href="https://royalsociety.org/grants-schemes-awards/book-prizes/science-book-prize/2015/life-on-the-edge/">use quantum mechanics to function optimally</a>. If this is indeed true, it means that our understanding of biology is radically incomplete. It also means that we could possibly control physiological processes by using the quantum properties of biological matter.</p>
<h2>Quantumness in biology is probably real</h2>
<p>Researchers can manipulate quantum phenomena to build better technology. In fact, you already live in a <a href="https://uwaterloo.ca/institute-for-quantum-computing/quantum-101/quantum-applications-today">quantum-powered world</a>: from laser pointers to GPS, magnetic resonance imaging and the transistors in your computer – all these technologies rely on quantum effects.</p>
<p>In general, quantum effects only manifest at very small length and mass scales, or when temperatures approach absolute zero. This is because quantum objects like atoms and molecules <a href="https://www.theatlantic.com/science/archive/2018/10/beyond-weird-decoherence-quantum-weirdness-schrodingers-cat/573448/">lose their “quantumness”</a> when they uncontrollably interact with each other and their environment. In other words, a macroscopic collection of quantum objects is better described by the laws of classical mechanics. Everything that starts quantum dies classical. For example, an electron can be manipulated to be in two places at the same time, but it will end up in only one place after a short while – exactly what would be expected classically.</p>
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<figcaption><span class="caption">Electrons can be in two places at the same time, but will end up in one location eventually.</span></figcaption>
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<p>In a complicated, noisy biological system, it is thus expected that most quantum effects will rapidly disappear, washed out in what the physicist Erwin Schrödinger called the “<a href="https://doi.org/10.1017/CBO9781139644129">warm, wet environment of the cell</a>.” To most physicists, the fact that the living world operates at elevated temperatures and in complex environments implies that biology can be adequately and fully described by classical physics: no funky barrier crossing, no being in multiple locations simultaneously.</p>
<p>Chemists, however, have for a long time begged to differ. Research on basic chemical reactions at room temperature unambiguously shows that <a href="https://doi.org/10.1063/5.0006547">processes occurring within biomolecules</a> like proteins and genetic material are the result of quantum effects. Importantly, such nanoscopic, short-lived quantum effects are consistent with driving some macroscopic physiological processes that biologists have measured in living cells and organisms. Research suggests that quantum effects influence biological functions, including <a href="https://doi.org/10.1146/annurev-biochem-051710-133623">regulating enzyme activity</a>, <a href="https://doi.org/10.1146/annurev-biophys-032116-094545">sensing magnetic fields</a>, <a href="https://doi.org/10.1038/srep38543">cell metabolism</a> and <a href="https://doi.org/10.1038/s41570-019-0087-1">electron transport in biomolecules</a>.</p>
<h2>How to study quantum biology</h2>
<p>The tantalizing possibility that subtle quantum effects can tweak biological processes presents both an exciting frontier and a challenge to scientists. Studying quantum mechanical effects in biology requires tools that can measure the short time scales, small length scales and subtle differences in quantum states that give rise to physiological changes – all integrated within a traditional wet lab environment.</p>
<p><a href="http://www.claricedaiello.com">In my work</a>, I build instruments to study and control the quantum properties of small things like electrons. In the same way that electrons have mass and charge, they also have a <a href="https://www.britannica.com/science/spin-atomic-physics">quantum property called spin</a>. Spin defines how the electrons interact with a magnetic field, in the same way that charge defines how electrons interact with an electric field. The quantum experiments I have been building <a href="https://doi.org/10.1038/ncomms2375">since graduate school</a>, and now in my own lab, aim to apply tailored magnetic fields to change the spins of particular electrons.</p>
<p>Research has demonstrated that many physiological processes are influenced by weak magnetic fields. These processes include <a href="https://doi.org/10.1126/sciadv.aau7201">stem cell development</a> and <a href="https://doi.org/10.1021/nn502923s">maturation</a>, <a href="https://doi.org/10.1371/journal.pone.0054775">cell proliferation rates</a>, <a href="https://doi.org/10.1021/acscentsci.8b00008">genetic material repair</a> and <a href="https://doi.org/10.1371/journal.pone.0179340">countless others</a>. These physiological responses to magnetic fields are consistent with chemical reactions that depend on the spin of particular electrons within molecules. Applying a weak magnetic field to change electron spins can thus effectively control a chemical reaction’s final products, with important physiological consequences.</p>
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<figcaption><span class="caption">Birds use quantum effects in navigation.</span></figcaption>
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<p>Currently, a lack of understanding of how such processes work at the nanoscale level prevents researchers from determining exactly what strength and frequency of magnetic fields cause specific chemical reactions in cells. Current cellphone, wearable and miniaturization technologies are already sufficient to produce <a href="https://doi.org/10.14814%2Fphy2.15189">tailored, weak magnetic fields that change physiology</a>, both for good and for bad. The missing piece of the puzzle is, hence, a “deterministic codebook” of how to map quantum causes to physiological outcomes.</p>
<p>In the future, fine-tuning nature’s quantum properties could enable researchers to develop therapeutic devices that are noninvasive, remotely controlled and accessible with a mobile phone. Electromagnetic treatments could potentially be used to prevent and treat disease, such as <a href="https://doi.org/10.1038/s41416-020-01136-5">brain tumors</a>, as well as in biomanufacturing, such as <a href="https://doi.org/10.1016/j.biomaterials.2022.121658">increasing lab-grown meat production</a>.</p>
<h2>A whole new way of doing science</h2>
<p>Quantum biology is one of the most interdisciplinary fields to ever emerge. How do you build community and train scientists to work in this area? </p>
<p>Since the pandemic, my lab at the University of California, Los Angeles and the University of Surrey’s Quantum Biology Doctoral Training Centre have organized <a href="https://groups.google.com/u/1/g/bigquantumbiologymeetings">Big Quantum Biology meetings</a> to provide an informal weekly forum for researchers to meet and share their expertise in fields like mainstream quantum physics, biophysics, medicine, chemistry and biology.</p>
<p>Research with potentially transformative implications for biology, medicine and the physical sciences will require working within an equally transformative model of collaboration. Working in one unified lab would allow scientists from disciplines that take very different approaches to research to conduct experiments that meet the breadth of quantum biology from the quantum to the molecular, the cellular and the organismal.</p>
<p>The existence of quantum biology as a discipline implies that traditional understanding of life processes is incomplete. Further research will lead to new insights into the age-old question of what life is, how it can be controlled and how to learn with nature to build better quantum technologies.</p><img src="https://counter.theconversation.com/content/204995/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Clarice D. Aiello receives funding from NSF, ONR, IDOR Foundation, Faggin Foundation, Templeton Foundation. </span></em></p>Studying the brief and tiny quantum effects that drive living systems could one day lead to new approaches to treatments and technologies.Clarice D. Aiello, Quantum Biology Tech (QuBiT) Lab, Assistant Professor of Electrical and Computer Engineering, University of California, Los AngelesLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2023082023-03-24T12:36:27Z2023-03-24T12:36:27ZHow do superconductors work? A physicist explains what it means to have resistance-free electricity<figure><img src="https://images.theconversation.com/files/517284/original/file-20230323-14-cz0c5g.jpg?ixlib=rb-1.1.0&rect=62%2C98%2C5928%2C3574&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Magnetic levitation is just one of the interesting attributes that make superconductors so interesting.</span> <span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/illustration/magnet-floating-above-a-superconductor-royalty-free-illustration/1301762762?phrase=superconductor&adppopup=true">Mark Garlick/Science Photo Library vie Getty Images</a></span></figcaption></figure><p>The modern world runs on electricity, and wires are what carry that electricity to every light, television, heating system, cellphone and computer on the planet. Unfortunately, on average, about <a href="https://www.nrdc.org/bio/jennifer-chen/lost-transmission-worlds-biggest-machine-needs-update">5%</a> of the power generated at a coal or solar power plant is lost as the electricity is transmitted from the plant to its final destination. This amounts to a <a href="https://www.nrdc.org/bio/jennifer-chen/lost-transmission-worlds-biggest-machine-needs-update">US$6 billion loss annually</a> in the U.S. alone. </p>
<p>For decades, scientists have been <a href="https://www.energy.gov/science/doe-explainssuperconductivity">developing materials called superconductors</a> that transmit electricity with nearly 100% efficiency. <a href="https://scholar.google.com/citations?user=5gCcMuMAAAAJ&hl=en&oi=sra">I am a physicist</a> who investigates how superconductors work at the atomic level, how current flows at very low temperatures, and how applications such as levitation can be realized. Recently, researchers have made significant progress toward developing superconductors that can function at <a href="https://doi.org/10.1088/1361-648X/ac2864">relatively normal temperatures and pressures</a>.</p>
<p>To see why these recent advances are so exciting and what impact they may have on the world, it’s important to understand how superconducting materials work.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/517258/original/file-20230323-1492-h3oux6.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Two lightbulbs next to each other with one showing a glowing filament." src="https://images.theconversation.com/files/517258/original/file-20230323-1492-h3oux6.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/517258/original/file-20230323-1492-h3oux6.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=517&fit=crop&dpr=1 600w, https://images.theconversation.com/files/517258/original/file-20230323-1492-h3oux6.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=517&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/517258/original/file-20230323-1492-h3oux6.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=517&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/517258/original/file-20230323-1492-h3oux6.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=650&fit=crop&dpr=1 754w, https://images.theconversation.com/files/517258/original/file-20230323-1492-h3oux6.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=650&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/517258/original/file-20230323-1492-h3oux6.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=650&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Most materials offer resistance when electricity runs through them and heat up. Resistance is how filaments in an incandescent lightbulb produce light.</span>
<span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:Carbonfilament.jpg#/media/File:Carbonfilament.jpg">Ulfbastel/Wikimedia Commons</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<h2>A resistance-free material</h2>
<p>A superconductor is any material that conducts electricity without offering any resistance to the flow of the electric current. </p>
<p>This resistance-free attribute of superconductors contrasts dramatically with <a href="https://sciencenotes.org/examples-of-conductors-and-insulators/">standard conductors</a> of electricity – like copper or aluminum – which heat up when current passes through them. This is similar to quickly sliding your hand across a smooth, slick surface compared to sliding your hand over a rough rug. The rug generates more friction and, therefore, more heat, too. Electric toasters and older-style incandescent lightbulbs use resistance to produce heat and light, but resistance can pose <a href="https://resources.pcb.cadence.com/blog/2022-the-influence-of-the-joule-heating-effect-on-pcbs-and-ics">problems for electronics</a>. Semiconductors have resistance below that of conductors, but still higher than that of superconductors. </p>
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<figcaption><span class="caption">Superconductive materials repel magnetic fields, making it possible to levitate a magnet above a superconductor.</span></figcaption>
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<p>Another characteristic of superconductors is that they repel magnetic fields. You may have seen videos of the fascinating result of this effect: It is possible to levitate magnets above a superconductor. </p>
<h2>How do superconductors work?</h2>
<p>All superconductors are made of materials that are electrically neutral – that is, their atoms contain negatively charged electrons that surround a nucleus with an equal number of positively charged protons. </p>
<p>If you attach one end of a wire to something that is positively charged, and the other end to something that is negatively charged, the system will want to reach equilibrium by moving electrons around. This causes the electrons in the wire to try to move through the material. </p>
<p>At normal temperatures, electrons move in somewhat erratic paths. They can generally succeed in moving through a wire freely, but every once in a while they collide with the nuclei of the material. These collisions are what obstruct the flow of electrons, cause resistance and heat up the material.</p>
<p>The nuclei of all atoms are constantly vibrating. In a superconducting material, instead of flitting around randomly, the moving electrons get passed along from atom to atom in such a way that they keep <a href="https://www.energy.gov/science/bes/articles/electrons-line-dance-superconductor#:%7E:text=Superconductors%20are%20materials%20that%20can,called%20a%20pair%20density%20wave.">in sync</a> with the vibrating nuclei. This coordinated movement produces no collisions and, therefore, no resistance and no heat.</p>
<p>The colder a material gets, the more organized the movement of electrons and nuclei becomes. This is why existing superconductors only work at extremely <a href="https://journals.aps.org/pr/abstract/10.1103/PhysRev.108.1175">low temperatures</a>. </p>
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<a href="https://images.theconversation.com/files/517262/original/file-20230323-14-bajdav.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A close-up view of a computer chip." src="https://images.theconversation.com/files/517262/original/file-20230323-14-bajdav.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/517262/original/file-20230323-14-bajdav.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=419&fit=crop&dpr=1 600w, https://images.theconversation.com/files/517262/original/file-20230323-14-bajdav.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=419&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/517262/original/file-20230323-14-bajdav.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=419&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/517262/original/file-20230323-14-bajdav.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=527&fit=crop&dpr=1 754w, https://images.theconversation.com/files/517262/original/file-20230323-14-bajdav.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=527&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/517262/original/file-20230323-14-bajdav.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=527&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Superconducting materials would allow engineers to fit many more circuits onto a single computer chip.</span>
<span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:Siliconchip_by_shapeshifter.png#/media/File:Siliconchip_by_shapeshifter.png">David Carron/Wikimedia Commons</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<h2>Benefits to electronics</h2>
<p>If scientists can develop a room-temperature superconducting material, wires and circuitry in electronics would be <a href="https://www.psfc.mit.edu/events/2017/high-temperature-superconductors-advantages-and-key-challenges-in-their-deployment-for">much more efficient</a> and produce far less heat. The benefits of this would be widespread.</p>
<p>If the wires used to transmit electricity were replaced with superconducting materials, these new lines would be able to carry up to <a href="https://phys.org/news/2014-05-longest-superconducting-cable-worldwide.html">five times as much electricity</a> more efficiently than current cables. </p>
<p>The speed of computers is mostly limited by how many wires can be packed into a single electric circuit on a chip. The density of wires is often <a href="https://link.springer.com/referenceworkentry/10.1007/978-0-387-09766-4_499">limited by waste heat</a>. If engineers could use superconducting wires, they could fit many more wires in a circuit, leading to faster and cheaper electronics.</p>
<p>Finally, with room-temperature superconductors, magnetic levitation could be used for <a href="https://www.intechopen.com/chapters/16183">all sorts of applications</a>, from trains to energy-storage devices.</p>
<p>With <a href="https://www.nytimes.com/2023/03/08/science/room-temperature-superconductor-ranga-dias.html">recent advances providing exciting news</a>, both researchers looking at the fundamental physics of high-temperature superconductivity as well as technologists waiting for new applications are paying attention.</p><img src="https://counter.theconversation.com/content/202308/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Mishkat Bhattacharya receives funding from the Office of Naval Research. </span></em></p>Superconductors are materials that can transmit electricity without any resistance. Researchers are getting closer to creating superconducting materials that can function in everyday life.Mishkat Bhattacharya, Professor of Physics and Astronomy, Rochester Institute of TechnologyLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1867372022-11-16T13:29:25Z2022-11-16T13:29:25ZPatients suffering with hard-to-treat depression may get relief from noninvasive magnetic brain stimulation<figure><img src="https://images.theconversation.com/files/477266/original/file-20220802-18-nnapcv.jpg?ixlib=rb-1.1.0&rect=15%2C0%2C5218%2C3931&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Transcranial magnetic stimulation has worked when medication and other therapies have not.</span> <span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/photo/patient-in-transcranial-magnetic-stimulation-royalty-free-image/548557027?adppopup=true">Monty Rakusen/Image Source via Getty Images</a></span></figcaption></figure><p>Not only is depression a debilitating disease, but it is also widespread. Approximately 20 million adult Americans experience at least <a href="https://www.nimh.nih.gov/health/statistics/major-depression">one episode of depression per year</a>. </p>
<p>Millions of them <a href="https://www.cdc.gov/nchs/products/databriefs/db377.htm#:">take medication</a> to treat their depression. But for many, the <a href="https://www.webmd.com/depression/guide/treatment-resistant-depression-what-is-treatment-resistant-depression">medications don’t work</a>: Either they have minimal or no effect, or the side effects are intolerable. These patients have what is called <a href="https://www.mayoclinic.org/diseases-conditions/depression/in-depth/treatment-resistant-depression/art-20044324">treatment-resistant depression</a>. </p>
<p>One promising treatment for such patients is a type of brain stimulation therapy <a href="https://www.healthline.com/health/tms-therapy#What-is-TMS-therapy">called transcranial magnetic stimulation</a>. </p>
<p>This treatment is not new; it has been around since 1995. The U.S. Food and Drug Administration <a href="https://doi.org/10.1016/j.brs.2021.11.010">cleared transcranial magnetic stimulation in 2008</a> for adults with “non-psychotic treatment-resistant depression,” which is typically defined as a failure to respond to two or more antidepressant medications. More recently, in 2018, the FDA cleared it for <a href="https://www.fda.gov/news-events/press-announcements/fda-permits-marketing-transcranial-magnetic-stimulation-treatment-obsessive-compulsive-disorder#">some patients with obsessive-compulsive disorder</a> and <a href="https://www.fda.gov/consumers/consumer-updates/want-quit-smoking-fda-approved-and-fda-cleared-cessation-products-can-help#">smoking cessation</a>. </p>
<p>Insurance <a href="https://www.mytransformations.com/post/the-ultimate-guide-to-tms-therapy-and-insurance-coverage">generally covers these treatments</a>. Both the psychiatrist and the equipment operator must be certified. While the treatment has been available for years, the equipment to perform the procedure remains expensive enough that few private psychiatry practices can afford it. But with the growing recognition of the potential of transcranial magnetic stimulation, the price will likely eventually come down and access will be greatly expanded.</p>
<h2>Does it work?</h2>
<p>Transcranial magnetic stimulation is a noninvasive, pain-free procedure that has minimal to no side effects, and it often works. Research shows that 58% of once treatment-resistant patients experience <a href="https://doi.org/10.1002/da.21969">a significant reduction in depression</a> following four to six rounds of the therapy. More than 40 independent clinical trials – with more than 2,000 patients worldwide – have demonstrated that repetitive transcranial magnetic stimulation <a href="https://doi.org/10.1136/gpsych-2019-100074">is an effective therapy</a> for the treatment of resistant major depression. </p>
<p><a href="https://medicine.fiu.edu/about/faculty-and-staff/profiles/psychiatry-and-behavioral-health/junquera,-patricia.html">As a professor and psychiatrist</a> who has used transcranial magnetic stimulation to treat some of my patients, I have seen depression symptoms decrease even within the first two weeks of treatment. What’s more, the effects continue after the treatment has ended, typically for six months to a year. After that, the patient has the option of maintenance treatment. </p>
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<figcaption><span class="caption">Transcranial magnetic stimulation helps increase blood flow and dopamine levels in the brain.</span></figcaption>
</figure>
<h2>About the procedure</h2>
<p>For the patient, the procedure is easy and simple. One sits in a comfortable chair with a snug pillow that holds their head in place, puts on earplugs and can then relax, check their phone, watch TV or read a book.</p>
<p>A treatment coil, which looks like a figure 8, is placed on the patient’s head. A nearby stimulator sends an electrical current to the coil, which transforms the current into <a href="https://www.livescience.com/38059-magnetism.html">a magnetic field</a>. </p>
<p>The field, which is highly concentrated, turns on and off rapidly while targeting a portion <a href="https://neuroscientificallychallenged.com/posts/know-your-brain-prefrontal-cortex">of the prefrontal cortex</a> – the area of the brain responsible for mood regulation. </p>
<p>Researchers know that people suffering from depression have reduced blood flow and less activity in that part of the brain. Transcranial magnetic stimulation causes increases in both blood flow and in the levels of <a href="https://www.healthdirect.gov.au/dopamine#">dopamine</a> and <a href="https://doi.org/10.1007/s00702-014-1180-8">glutamate</a> – two neurotransmitters that are responsible for brain functions like concentration, memory and sleep. It’s the repeated stimulation of this area – the “depression circuit” of the brain – that brings the antidepressant effect. </p>
<h2>It is not ‘electroshock’ or deep brain stimulation</h2>
<p>Some people confuse transcranial magnetic stimulation with <a href="https://www.psychiatry.org/patients-families/ect#">electroconvulsive therapy</a>, a procedure used for patients with severe depression or catatonia. With electroshock therapy, the anesthetized patient receives a direct electrical current, which causes a seizure. Typically, people who undergo this procedure experience <a href="https://www.mayoclinic.org/tests-procedures/electroconvulsive-therapy/about/pac-20393894#:">some memory loss after treatment</a>. </p>
<p>Transcranial magnetic stimulation is very different. It doesn’t require anesthesia, and it doesn’t affect memory. The patient can resume daily activities right after each treatment. Dormant brain connections are reignited without causing a seizure.</p>
<p>It should also not be confused with <a href="https://www.mayoclinic.org/tests-procedures/deep-brain-stimulation/about/pac-20384562">deep brain stimulation</a>, which is a surgical procedure used <a href="https://theconversation.com/deep-brain-stimulation-can-be-life-altering-for-ocd-sufferers-when-other-treatment-options-fall-short-186109">to treat obsessive-compulsive disorder</a>, tremors, epilepsy and Parkinson’s disease. </p>
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<figcaption><span class="caption">Transcranial magnetic stimulation stimulates the ‘depression circuit’ in the brain.</span></figcaption>
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<h2>Side effects and access</h2>
<p>Transcranial magnetic stimulation patients undergo a total of <a href="https://www.mindpath.com/resource/what-a-typical-tms-treatment-looks-like/">36 treatments, at 19 minutes each</a>, for three to six weeks. Research has concluded that this is the best protocol for treatment. Some patients report that it feels like someone is tapping on their head. Others don’t feel anything. </p>
<p>Some very minor side effects may occur. The most common is facial twitching and scalp discomfort during treatment, sensations that go away after the session ends. Some patients report a mild headache or discomfort at the application site. Depending on how effective the therapy was, some patients return for follow-ups every few weeks or months. It can be used in addition to medications, or with no medication at all. </p>
<p>Not everyone with depression can undergo <a href="https://www.clinicaltmssociety.org/content/who-cannot-have-tms">this type of brain stimulation therapy</a>. Those with epilepsy or a history of head injury may not qualify. People with metallic fillings in their teeth are OK for treatment, but others with implanted, nonremovable metallic devices in or around the head are not. Those with pacemakers, defibrillators and vagus nerve stimulators may also not qualify, because the magnetic force of the treatment coil may dislodge these devices and cause severe pain or injury. </p>
<p>But for those who are able to use the therapy, the results can be remarkable. For me, it is amazing to see these patients smile again – and come out on the other side feeling hopeful.</p><img src="https://counter.theconversation.com/content/186737/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Patricia Junquera does not work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>Patients who undergo transcranial magnetic stimulation say it’s painless, with few to no side effects. The treatment isn’t yet widely accessible, but for those who use it, the effects can be profound.Patricia Junquera, Associate Professor and Vice Chair of Clinical Services, Florida International UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1613922021-05-24T15:16:06Z2021-05-24T15:16:06ZThe Sun’s atmosphere is hundreds of times hotter than its surface – here’s why<figure><img src="https://images.theconversation.com/files/402311/original/file-20210524-15-ve369u.jpeg?ixlib=rb-1.1.0&rect=0%2C0%2C5120%2C2880&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><a class="source" href="https://www.shutterstock.com/image-illustration/sun-solar-atmosphere-isolated-on-black-1816367882">Mongta Studio/Shutterstock</a></span></figcaption></figure><p>The visible surface of the Sun, or the <a href="https://www.britannica.com/science/photosphere">photosphere</a>, is around 6,000°C. But a few thousand kilometres above it – a small distance when we consider the size of the Sun – the solar atmosphere, also called the <a href="https://www.britannica.com/science/corona-Sun">corona</a>, is hundreds of times hotter, reaching a million degrees celsius or higher. </p>
<p>This spike in temperature, despite the increased distance from the Sun’s main energy source, has been observed in most stars, and represents a <a href="https://science.nasa.gov/news-articles/the-mystery-of-coronal-heating">fundamental puzzle</a> that astrophysicists have mulled over for decades.</p>
<p>In 1942, the Swedish scientist Hannes Alfvén <a href="https://www.nature.com/articles/150405d0">proposed an explanation</a>. He theorised that magnetised waves of plasma could carry huge amounts of energy along the Sun’s magnetic field from its interior to the corona, bypassing the photosphere before exploding with heat in the Sun’s upper atmosphere.</p>
<p>The theory had been tentatively accepted – but we still needed proof, in the form of empirical observation, that these waves existed. <a href="https://www.nature.com/articles/s41550-021-01354-8">Our recent study</a> has finally achieved this, validating Alfvén’s 80 year-old theory and taking us a step closer to harnessing this high-energy phenomenon here on Earth.</p>
<h2>Burning questions</h2>
<p>The <a href="https://www.nasa.gov/feature/goddard/2018/nasa-s-parker-solar-probe-and-the-curious-case-of-the-hot-corona/">coronal heating problem</a> has been established since the late 1930s, when the Swedish spectroscopist Bengt Edlén and the German astrophysicist Walter Grotrian first observed phenomena in the Sun’s corona that could only be present if its temperature was <a href="https://www.frontiersin.org/articles/10.3389/fspas.2018.00009/full">a few million degrees celsius</a>. </p>
<p>This represents temperatures up to 1,000 times hotter than the photosphere beneath it, which is the surface of the Sun that we can see from Earth. Estimating the photosphere’s heat has always been relatively straightforward: we just need to <a href="https://astronomy.com/magazine/ask-astro/2018/01/measuring-the-suns-temperature">measure the light</a> that reaches us from the Sun, and compare it to spectrum models that predict the temperature of the light’s source. </p>
<p>Over many decades of study, the photosphere’s temperature has been consistently estimated at around 6,000°C. Edlén and Grotrian’s finding that the Sun’s corona is so much hotter than the photosphere – despite being further from <a href="https://www.space.com/17137-how-hot-is-the-sun.html">the Sun’s core</a>, its ultimate source of energy – has led to much head scratching in the scientific community. </p>
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<figcaption><span class="caption">The extreme heat of the Sun’s corona is one of the most vexing problems in astrophysics.</span></figcaption>
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<p>Scientists looked to the Sun’s properties to explain this disparity. The Sun is composed almost entirely of plasma, which is highly ionised gas that carries an electrical charge. The movement of this plasma in the <a href="https://www.esa.int/ESA_Multimedia/Images/2019/10/Anatomy_of_our_Sun">convection zone</a> – the upper part of the solar interior – produces huge electrical currents and strong magnetic fields.</p>
<p>These fields are then dragged up from the Sun’s interior by convection, and burble onto its visible surface in the form of <a href="https://www.sciencedirect.com/science/article/abs/pii/S027311771500616X">dark sunspots</a>, which are clusters of magnetic fields that can form a variety of magnetic structures in the solar atmosphere.</p>
<p>This is where Alfvén’s theory comes in. He reasoned that within the Sun’s magnetised plasma any bulk motions of electrically charged particles would disturb the magnetic field, creating waves that can carry huge amounts of energy along vast distances – from the Sun’s surface to its upper atmosphere. The heat travels along what are called <a href="https://iopscience.iop.org/article/10.3847/1538-4357/abec7a">solar magnetic flux tubes</a> before bursting into the corona, producing its high temperature.</p>
<figure class="align-center ">
<img alt="A diagram of the sun's different features" src="https://images.theconversation.com/files/402336/original/file-20210524-19-jj94xe.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/402336/original/file-20210524-19-jj94xe.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=426&fit=crop&dpr=1 600w, https://images.theconversation.com/files/402336/original/file-20210524-19-jj94xe.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=426&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/402336/original/file-20210524-19-jj94xe.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=426&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/402336/original/file-20210524-19-jj94xe.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=535&fit=crop&dpr=1 754w, https://images.theconversation.com/files/402336/original/file-20210524-19-jj94xe.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=535&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/402336/original/file-20210524-19-jj94xe.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=535&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
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<span class="caption">Sunspots are darker patches on the Sun’s surface.</span>
<span class="attribution"><a class="source" href="https://www.shutterstock.com/image-vector/sun-structure-diagram-vector-illustration-internal-1181453593">Siberian Art/Shutterstock</a></span>
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<p>These magnetic plasma waves are now called Alfvén waves, and their part in explaining coronal heating led to Alfvén being awarded the <a href="https://www.nobelprize.org/prizes/physics/1970/summary/">Nobel Prize in Physics in 1970</a>.</p>
<h2>Observing Alfvén waves</h2>
<p>But there remained the problem of actually observing these waves. There’s so much happening on the Sun’s surface and in its atmosphere – from phenomena many times larger than Earth to small changes below the resolution of our instrumentation – that direct observational evidence of Alfvén waves in the photosphere has not been achieved before. </p>
<p>But recent advances in instrumentation have opened a new window through which we can examine solar physics. One such instrument is the <a href="http://www.arcetri.astro.it/science/solare/IBIS/">Interferometric Bidimensional Spectropolarimeter</a> (IBIS) for imaging spectroscopy, installed at the Dunn Solar Telescope in the US state of New Mexico. This instrument has allowed us to make far more detailed observations and measurements of the Sun.</p>
<p>Combined with good viewing conditions, advanced computer simulations, and the efforts of an international team of scientists from seven research institutions, we used the IBIS to <a href="https://www.nature.com/articles/s41550-021-01354-8">finally confirm</a>, for the first time, the existence of Alfvén waves in solar magnetic flux tubes. </p>
<h2>New energy source</h2>
<p>The direct discovery of Alfvén waves in the solar photosphere is an important step towards exploiting their high energy potential here on Earth. They could help us research <a href="https://www.bbc.co.uk/news/uk-england-nottinghamshire-56256144">nuclear fusion</a>, for instance, which is the process taking place <a href="https://www.nature.com/articles/d41586-020-01908-2/">inside the Sun</a> that involves small amounts of matter being converted into huge amounts of energy. Our current nuclear power stations use <a href="https://www.sciencedirect.com/topics/physics-and-astronomy/nuclear-fission">nuclear fission</a>, which critics argue produces dangerous nuclear waste – especially in the case of disasters including the one that took place in <a href="https://theconversation.com/fukushima-ten-years-on-from-the-disaster-was-japans-response-right-156554">Fukushima</a> in 2011.</p>
<p>Creating clean energy by replicating the nuclear fusion of the Sun on Earth remains a huge challenge, because we’d still need to generate 100 million degrees celsius quickly for fusion to occur. Alfvén waves could be one way of doing this. Our growing knowledge of the Sun shows it’s certainly possible – under the right conditions. </p>
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<a href="https://theconversation.com/nuclear-fusion-building-a-star-on-earth-is-hard-which-is-why-we-need-better-materials-155917">Nuclear fusion: building a star on Earth is hard, which is why we need better materials</a>
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<p>We’re also expecting more solar revelations soon, thanks to new, ground-breaking missions and instruments. The European Space Agency’s <a href="https://www.esa.int/Science_Exploration/Space_Science/Solar_Orbiter">Solar Orbiter satellite</a> is now in orbit around the Sun, delivering images and taking measurements of the star’s uncharted polar regions. Terrestrially, the unveiling of new, high-performance <a href="https://est-east.eu/est-project">solar telescopes</a> are also expected to enhance our observations of the Sun from Earth.</p>
<p>With many secrets of the Sun still to be discovered, including the properties of the Sun’s <a href="http://hspf.eu/samnet.html">magnetic field</a>, this is an exciting time for solar studies. Our detection of Alfvén waves is just one contribution to a wider field that’s looking to unlock the Sun’s remaining mysteries for practical applications on Earth.</p><img src="https://counter.theconversation.com/content/161392/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span> Marianna Korsos receives funding from STFC</span></em></p><p class="fine-print"><em><span>Huw Morgan receives funding from STFC (UKRI), Leverhulme, and European Regional Development Funds through the Welsh Government. </span></em></p>Alfvén waves, first proposed 80 years ago, could explain why the sun’s atmosphere is so much hotter than its surface.Marianna Korsos, Post-Doctoral Research Assistant, Department of Physics, Aberystwyth UniversityHuw Morgan, Reader in Physical Sciences, Aberystwyth UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1598952021-05-05T15:52:51Z2021-05-05T15:52:51ZSpace weather is difficult to predict — with only an hour to prevent disasters on Earth<figure><img src="https://images.theconversation.com/files/397967/original/file-20210429-19-3t3kvx.jpg?ixlib=rb-1.1.0&rect=7%2C39%2C5250%2C6535&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">The interaction of solar winds and the Earth’s atmosphere produces the northern lights that dance across the night sky. </span> <span class="attribution"><span class="source">(Benjamin Suter/Unsplash)</span>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span></figcaption></figure><p>Recent developments at the forefront of astronomy allow us to observe that <a href="https://www.cnn.com/2021/04/13/world/raindrops-other-planets-scn/index.html">planets orbiting other stars have weather</a>. Indeed, we have known that other planets in our own solar system have weather, in many cases more extreme than our own. </p>
<p>Our lives are affected by short-term atmospheric variations of weather on Earth, and we fear that longer-term climate change will also have a large impact. The recently coined term “space weather” refers to effects that arise in space but affect Earth and regions around it. More subtle than meteorological weather, space weather usually acts on technological systems, and has potential impacts that range from communication disruption to power grid failures.</p>
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<a href="https://theconversation.com/solar-weather-has-real-material-effects-on-earth-118453">Solar weather has real, material effects on Earth</a>
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<p>An ability to predict space weather is an essential tool in providing warnings so that mitigation can be attempted, and to hopefully, in extreme cases, forestall a disaster. </p>
<h2>The history of weather forecasting</h2>
<p>We are now used to large-scale meteorological forecasts that are quite accurate for about a two-week timescale. </p>
<p>Scientific weather forecasting originated about a century ago, with the term <a href="https://www.smithsonianmag.com/history/how-world-war-i-changed-weather-good-180963360/">“front” being associated with the First World War</a>. Meteorological prediction is based on a good knowledge of underlying theory, codified into massive computer programs running on the most advanced computers, with huge amounts of input data. </p>
<p>Important aspects of weather, like moisture content, can be measured by satellites that monitor continuously. Other measurements are also be readily taken, for example, by the nearly 2,000 weather balloons launched each day. Exploring the limits in weather forecasting gave rise to chaos theory, sometimes called the “butterfly effect.” The buildup of error brings about the two-week practical limit. </p>
<p>In contrast, the prediction of space weather is only truly reliable about one hour in advance!</p>
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<figcaption><span class="caption">An explainer of the science behind chaos.</span></figcaption>
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<h2>Solar effects</h2>
<p>Most space weather <a href="https://www.nasa.gov/mission_pages/sunearth/spaceweather/index.html">originates from the sun</a>. Its outermost atmosphere blows into space at supersonic speeds, although at such low density that interplanetary space is more rarified than what is considered a vacuum in our laboratories. Unlike winds on Earth, this solar wind carries along a magnetic field. This is much smaller than Earth’s own field that we can detect with a compass at the surface, and vastly smaller than that near a fridge magnet, but it can interact with Earth, with an important role in space weather. </p>
<p>The very thin solar wind, with a very weak magnetic field, can nevertheless affect Earth in part because it interacts with a large magnetic bubble around Earth, called the magnetosphere, over a very large area, at least a hundred times as big as the surface of our planet. Much like a breeze that can barely move a thread can move a huge sailing ship when caught on the large sails, the effect of solar wind, through its direct pressure (like on a sail) or through its magnetic field interacting with Earth’s, can be enormous. </p>
<p>As the origin point, the sun itself is a seething mass of hot gas and magnetic fields, and their interaction is complex, sometimes even explosive. Magnetic fields are concentrated near sunspots, and <a href="https://earthobservatory.nasa.gov/world-of-change/Solar">produce electromagnetic phenomena like solar flares (the name says it all) and coronal mass ejections</a>. Much as with tornadoes on Earth, we know generally when conditions are favourable for these localized explosions, but precise prediction is difficult. </p>
<p>Even once an event is detected, if a large mass of fast, hot and dense gas is shot in our direction (and such a “cloud” in turn is difficult to detect, coming at us against the glare of the sun), there is a further complicating factor in predicting its danger.</p>
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<figcaption><span class="caption">NASA scientists answer questions about space weather.</span></figcaption>
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<h2>Detecting magnetic fields</h2>
<p>Unlike the detectable, sometimes even visible, water content in the atmosphere that is so important in meteorology, the magnetic field of gas ejected from the sun, including in hot and denser clouds from explosions, is almost impossible to detect from afar. The effect of an interplanetary cloud is greatly enhanced if the direction of its magnetic field is opposite to Earth’s own field where it hits the barrier of Earth’s magnetosphere. In that case, a process known as “reconnection” allows much of the cloud’s energy to be transferred to the region near Earth, and accumulate largely on the night side, despite the cloud hitting on the side facing the sun. </p>
<p>By secondary processes, usually involving further reconnection, this energy produces space weather effects. Earth’s <a href="https://www.space.com/33948-van-allen-radiation-belts.html">radiation belts can be greatly energized</a>, endangering astronauts and even satellites. These processes can also produce bright auroras, whose beauty hides danger since they in turn produce magnetic fields. A generator effect takes place when dancing auroras make magnetic fields vary, but unlike in the generators that produce much of our electricity, the electric fields from auroras are uncontrolled. </p>
<p>The electric fields from auroras are small, and undetectable to human senses. However, over a very large region they can build up to apply a considerable voltage. It’s this effect that poses a hazard to our largest infrastructure, such as electric grids. To predict when this might happen, we would need to measure from afar the size and direction of magnetic field in an incoming space cloud. However, that invisible field is stealthy and hard to detect until it is nearly upon us.</p>
<h2>Satellite monitors</h2>
<p>By the gravitational laws of orbits, a satellite continuously monitoring magnetic fields by direct measurement must sit about a million miles (1.6 million kilometres) from Earth, between us and the sun a hundred times further away. A magnetic cloud causing minor space weather effects usually takes about three days to come from the sun to Earth. A truly dangerous cloud, from a bigger solar explosion, may take as little as a day. Since our monitoring satellites are relatively close to Earth, we only know about the crucial magnetic field direction at most one hour in advance of impact. This is not much time to prepare vulnerable infrastructure, like power and communication networks and satellites, to best survive.</p>
<p>Since the fleets of satellites needed to give better warning are not even on the drawing boards, we must rely on luck in the face of space weather. It may be a small comfort that the coming solar maximum — when the surface of the sun is at its most active during a cycle and is expected to peak in 2025 — <a href="https://www.nasa.gov/press-release/solar-cycle-25-is-here-nasa-noaa-scientists-explain-what-that-means">is predicted to be mild</a>. </p>
<p>It may be Mark Twain who said “it is hard to make predictions, especially about the future,” but it is certainly true in the case of space weather.</p><img src="https://counter.theconversation.com/content/159895/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Martin Gerard Connors receives funding from NSERC, the Canada Foundation for Innovation, Alberta Innovation, and the Canadian Space Agency. </span></em></p>It has only been in the past century that weather prediction on Earth has advanced enough to work two weeks in advance. Predicting space weather, however, is only reliable an hour in advance.Martin Connors, Professor of Space Science and Physics, Athabasca UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1550402021-02-15T04:00:08Z2021-02-15T04:00:08ZWe found the first Australian evidence of a major shift in Earth’s magnetic poles. It may help us predict the next<figure><img src="https://images.theconversation.com/files/384156/original/file-20210215-21-1bbrzt.jpg?ixlib=rb-1.1.0&rect=20%2C37%2C2227%2C1085&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><span class="source">NASA</span></span></figcaption></figure><p>About 41,000 years ago, something remarkable happened: Earth’s magnetic field flipped and, for a temporary period, magnetic north was south and magnetic south was north. </p>
<p><a href="https://www.nature.com/subjects/palaeomagnetism">Palaeomagnetists</a> refer to this as a geomagnetic excursion. This event, which is different to a complete magnetic pole reversal, occurs irregularly through time and reflects the dynamics of Earth’s molten <a href="https://www.nationalgeographic.org/encyclopedia/core/">outer core</a>. </p>
<p>The strength of Earth’s magnetic field would have almost vanished during the event, called the Laschamp excursion, which lasted a <a href="https://www.frontiersin.org/articles/10.3389/feart.2019.00086/full">few thousand years</a>. </p>
<p>Earth’s magnetic field acts as a shield against high-energy particles from the Sun and outside the solar system. Without it the planet would be bombarded by these charged particles. </p>
<p>We don’t know when the next geomagnetic excursion will happen. But if it happened today, it would be crippling. </p>
<p>Satellites and navigation apps would be rendered useless — and power distribution systems would be disrupted at a cost of <a href="https://agupubs.onlinelibrary.wiley.com/doi/full/10.1002/2016SW001491">between</a> US$7 billion and US$48 billion each day in the United States alone.</p>
<p>Obviously, satellites and electric grids didn’t exist 41,000 years ago. But the Laschamp excursion — named after the lava flows in France where it was first recognised — still left its mark. </p>
<p>We recently detected its signature in Australia for the first time, in a 5.5 metre-long sediment core taken from the bottom of Lake Selina, Tasmania. </p>
<p>Within these grains lay 270,000 years of history, which we unpack in <a href="https://www.sciencedirect.com/science/article/abs/pii/S1871101421000030">our paper</a> published in the journal Quaternary Geochronology. </p>
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<a href="https://theconversation.com/explainer-what-happens-when-magnetic-north-and-true-north-align-123265">Explainer: what happens when magnetic north and true north align?</a>
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<h2>How sediment can record Earth’s magnetic field</h2>
<p>Rock and soil can naturally contain magnetic particles, such as the iron mineral <a href="https://www.sciencedirect.com/topics/engineering/magnetite">magnetite</a>. These magnetic particles are like tiny compass needles aligned with Earth’s magnetic field. </p>
<p>They can be carried from the landscape into lakes through rainfall and wind. They eventually accumulate on the lake’s bottom, becoming buried and locking in place. They effectively become a fossil record of Earth’s magnetic field. </p>
<p>Scientists can then drill into lake beds and use a device called a magnetometer to recover the information held by the lake sediment. The deeper we drill, the further back in time we go.</p>
<p>In 2014 my colleagues and I travelled to Lake Selina in Tasmania with the goal of extracting the area’s climate, vegetation and “paleomagnetic” record, which is the record of Earth’s magnetic field stored in rocks, sediment and other materials.</p>
<p>Led by University of Melbourne Associate Professor <a href="https://findanexpert.unimelb.edu.au/profile/6089-michael-shawn-fletcher">Michael-Shawn Fletcher</a>, we drilled into the lake floor from a makeshift floating platform rigged to two inflatable rafts.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/384153/original/file-20210215-15-1accaw6.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Lake Selina, Tasmania." src="https://images.theconversation.com/files/384153/original/file-20210215-15-1accaw6.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/384153/original/file-20210215-15-1accaw6.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=425&fit=crop&dpr=1 600w, https://images.theconversation.com/files/384153/original/file-20210215-15-1accaw6.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=425&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/384153/original/file-20210215-15-1accaw6.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=425&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/384153/original/file-20210215-15-1accaw6.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=533&fit=crop&dpr=1 754w, https://images.theconversation.com/files/384153/original/file-20210215-15-1accaw6.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=533&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/384153/original/file-20210215-15-1accaw6.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=533&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Lake Selina is a small sub-alpine lake located near the west coast of Tasmania. Sediment from the lake was sampled in the form of 2x2cm cubes, each containing a few hundred years’ worth of magnetic field history.</span>
<span class="attribution"><span class="source">Michael-Shawn Fletcher</span>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<h2>The first Australian evidence of Laschamp</h2>
<p>Our dating of the core revealed that the biggest shift in magnetic pole positions and the lowest magnetic field intensity at Lake Selina both occurred during the Laschamp excursion.</p>
<p>But for a core that spanned several glacial periods, no single dating method could be trusted to precisely determine its age. So we employed numerous scientific techniques including radiocarbon dating and beryllium isotope <a href="https://www.cerege.fr/fr/equipements/ln2c">analysis</a>.</p>
<p>The latter involves tracking the presence of an isotope called beryllium-10. This is formed when high-energy cosmic particles bombard Earth, colliding with oxygen and nitrogen atoms in the atmosphere. </p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/new-evidence-for-a-human-magnetic-sense-that-lets-your-brain-detect-the-earths-magnetic-field-113536">New evidence for a human magnetic sense that lets your brain detect the Earth's magnetic field</a>
</strong>
</em>
</p>
<hr>
<p>Since a weaker magnetic field leads to more of these charged particles bombarding Earth, we expected to find more beryllium-10 in sediment containing magnetic particles “locked-in” during the Laschamp excursion. Our findings confirmed this.</p>
<p>The interaction between charged cosmic particles and air particles in Earth’s atmosphere is also what creates auroras. Several generations of people would have witnessed a plethora of spectacular auroras during the Laschamp excursion. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/384141/original/file-20210214-19-1q3v064.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Aurora borealis over the Gulf of Finland." src="https://images.theconversation.com/files/384141/original/file-20210214-19-1q3v064.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/384141/original/file-20210214-19-1q3v064.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=397&fit=crop&dpr=1 600w, https://images.theconversation.com/files/384141/original/file-20210214-19-1q3v064.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=397&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/384141/original/file-20210214-19-1q3v064.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=397&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/384141/original/file-20210214-19-1q3v064.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=499&fit=crop&dpr=1 754w, https://images.theconversation.com/files/384141/original/file-20210214-19-1q3v064.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=499&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/384141/original/file-20210214-19-1q3v064.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=499&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The interaction between charged cosmic particles and the highest air particles in Earth’s atmosphere is what creates auroras. During the Laschamp excursion, several generations of people would have witnessed a plethora of spectacular auroras.</span>
<span class="attribution"><span class="source">Shutterstock</span></span>
</figcaption>
</figure>
<h2>Building on work from the 1980s</h2>
<p>Only two other lakes in Australia — Lake Barrine and Lake Eacham in Queensland — have provided a “full-vector” record, wherein both the <a href="https://academic.oup.com/gji/article/81/1/103/674602">past directions</a> and <a href="https://academic.oup.com/gji/article/81/1/121/674627">past intensity</a> of the magnetic field are obtained from the same core. </p>
<p>But at 14,000 years old, the records from these lakes are much younger than the Laschamp excursion. Four decades later, our work at Lake Selina with modern techniques has revealed the exciting potential for similar research at other Australian lakes. </p>
<p>Currently, Australia is considered a paleomagnetic “blind spot”. </p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/384170/original/file-20210215-23-1eo00yc.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Stalactites hang from cave ceiling." src="https://images.theconversation.com/files/384170/original/file-20210215-23-1eo00yc.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/384170/original/file-20210215-23-1eo00yc.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=600&fit=crop&dpr=1 600w, https://images.theconversation.com/files/384170/original/file-20210215-23-1eo00yc.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=600&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/384170/original/file-20210215-23-1eo00yc.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=600&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/384170/original/file-20210215-23-1eo00yc.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=754&fit=crop&dpr=1 754w, https://images.theconversation.com/files/384170/original/file-20210215-23-1eo00yc.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=754&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/384170/original/file-20210215-23-1eo00yc.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=754&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">‘Speleothems’ such as stalactites (pictured) and stalagmites are mineral deposits that form in caves.</span>
<span class="attribution"><span class="source">Shutterstock</span></span>
</figcaption>
</figure>
<p>More data from lake sediments, archaeological artefacts, lava flows and mineral <a href="https://www.sciencedirect.com/topics/earth-and-planetary-sciences/speleothem">cave formations</a>, including stalagmites and stalactites, could greatly improve our understanding of Earth’s magnetic field. </p>
<p>With this knowledge, we may one day potentially be able to predict the next geomagnetic excursion, before our phones stop working and the birds overhead veer off-course and crash into windows.</p>
<p>Our dating of the Lake Selina core is just the start. We’re sure there are more secrets embedded beneath, waiting to be found. And so we continue our search.</p>
<hr>
<p><em>This work was carried out in collaboration with <a href="http://www.archaeomagnetism.com/taal-lab-facilities">La Trobe University</a>, the <a href="http://rses.anu.edu.au/research/facilities/palaeomagnetic-laboratory">Australian National University</a>, The University of Wollongong, the Australian Nuclear Science and Technology Organisation and the European Centre for Research and Teaching in Environmental Geosciences (<a href="https://www.cerege.fr/fr/equipements/ln2c">CEREGE</a>).</em></p><img src="https://counter.theconversation.com/content/155040/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Agathe Lise-Pronovost receives funding from the Australian Research Council. </span></em></p>Researchers have found the first Australian evidence of this global event, during which people on Earth would have witnessed a multitude of spectacular auroras.Agathe Lise-Pronovost, McKenzie Research Fellow in Earth Sciences, The University of MelbourneLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1549922021-02-14T10:34:12Z2021-02-14T10:34:12ZBirds use massive magnetic maps to migrate – and some could cover the whole world<figure><img src="https://images.theconversation.com/files/384033/original/file-20210212-13-18dji0c.jpg?ixlib=rb-1.1.0&rect=35%2C0%2C5955%2C3341&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/silhouette-birds-flying-over-blue-mountains-1843997779">muratart/Shutterstock</a></span></figcaption></figure><p>Every year, billions of songbirds migrate thousands of miles between Europe and Africa – and then repeat that same journey again, year after year, to nest in exactly the same place that they chose on their first great journey.</p>
<p>The remarkable <a href="https://besjournals.onlinelibrary.wiley.com/doi/full/10.1046/j.1365-2656.2002.00599.x">navigational precision</a> displayed by these tiny birds – as they travel alone over stormy seas, across vast deserts, and through extremes in weather and temperature – has been one of the enduring mysteries of behavioural biology. </p>
<p>We know that birds buffeted by winds so much that they’re significantly displaced from their migratory route are able to <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2084305/">realign their course</a> if they’ve already performed one migration. This has suggested that birds’ navigational abilities – some of which is built around a sense of compass direction – includes a mechanism for finding their way back home from parts of the world they’ve never before visited.</p>
<p>Now, <a href="https://www.cell.com/current-biology/fulltext/S0960-9822(21)00116-0">our new study</a> of Eurasian reed warblers has found that this remarkable ability involves a “magnetic map” that works like our human system of coordinates. Surprisingly, our study found that these birds understand the magnetic field of places thousands of miles into territory they’ve never before visited – suggesting some birds could possess a “global GPS system” that can tell them how to get home from anywhere on Earth.</p>
<h2>Mind maps</h2>
<p>It’s long been known that adult birds develop some sort of navigational map to help them migrate. How they do this has remained controversial. <a href="https://zslpublications.onlinelibrary.wiley.com/doi/full/10.1111/jzo.12107">Several cues have been proposed</a> as guides for migratory birds – including odours, infra-sound, and even variations in gravity.</p>
<p>However, a <a href="https://www.sciencedirect.com/science/article/pii/S0960982215009549">gathering body of evidence</a> has indicated that the Earth’s magnetic field is one of the likeliest solutions to this mystery. It has been suggested that different parameters of the Earth’s magnetic field <a href="https://www.sciencedirect.com/science/article/pii/S0960982217308825">could form a grid</a>, which birds follow, of north-south and east-west lines. </p>
<p>That’s because magnetic intensity (the strength of the magnetic field) and magnetic inclination (the angle formed between the magnetic field lines and the surface of the Earth, also called the “dip” angle) both run approximately north to south. Magnetic declination – the difference between the direction to the magnetic north pole and the geographical north pole – provides the east-west axis. </p>
<p>Despite largely agreeing that certain birds navigate via the Earth’s magnetic field, scientists haven’t worked out precisely what sensory apparatus they use to detect it – or whether multiple systems are used to detect different parameters of the field. Other animals, like turtles, can also sense the magnetic field, but the same uncertainties apply.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/migrating-birds-use-a-magnetic-map-to-travel-long-distances-82624">Migrating birds use a magnetic map to travel long distances</a>
</strong>
</em>
</p>
<hr>
<p>Regardless, if birds have learned that magnetic intensity increases as they go north, they should be able to detect their position on the north-south axis wherever they happen to be. Similarly, if they experience a declination value that is greater than anything they’ve previously experienced, they should know they’re further east. On this basis, the theory is that they can calculate their position on the grid and correct their orientation. </p>
<p>This would mean that birds essentially navigate using a system similar to our Cartesian coordinates – the basis of modern GPS navigation. If this coordinates theory is accurate, it would mean that birds should be able to use their knowledge of magnetic field parameters to estimate their location anywhere on Earth – through the extrapolation or extension of their navigational rules.</p>
<p>To date, however, there has been no clear evidence that birds can use the magnetic field in this way. But <a href="https://www.cell.com/current-biology/fulltext/S0960-9822(21)00116-0">our new study</a> on the migratory Eurasian reed warbler – or the <em>Acrocephalus scirpaceus</em> – is the first to show clear evidence that they can in fact do this. </p>
<h2>Untrue north</h2>
<p>To prove the coordinates theory, we used a technique called “virtual displacement”. We tested birds’ orientation behaviour by placing them in a small cage called an “Emlen funnel”. When a bird tries to fly from the cage, it leaves scratches in the direction it’s trying to fly towards.</p>
<p>Remarkably, we found that this corresponded to the direction that it would be trying to migrate in the wild, which we know from <a href="https://academic.oup.com/auk/article-abstract/83/3/361/5208449?redirectedFrom=fulltext">previous experiments</a>. To test whether birds plot their course from takeoff using magnetic fields, we put the Emlen funnels inside a “Helmholtz coil” – a device that allows us to change the nature of the magnetic field in the immediate vicinity of the bird.</p>
<p>In doing so, we created a virtual displacement. The bird does not move: it is tested at the site where it is captured, with all other variables remaining the same – apart from the magnetic field, which we changed to match a location far to the north east of their normal range. We chose the location so that it would be far beyond any magnetic field the warblers would have previously experienced. </p>
<p>Only if the birds were able to map their location based on the magnetic field around them would they recognise their displacement – and indeed they did, shifting their takeoff to fly in the “wrong” direction in the real world, but the “right” direction in the magnetic world we’d created around their Emlen funnels.</p>
<h2>Winging it</h2>
<p>While this cue may be relevant for reed warblers and other migratory songbirds, it is by no means the only navigation system used by birds. Other birds, including seabirds and homing pigeons, have been shown to <a href="https://www.nature.com/articles/srep17061">require olfactory cues</a> (scents and smells) to navigate. At this stage, we don’t understand the reason behind these different preferences.</p>
<p>And, while we are closer to understanding the mystery of how birds navigate using magnetic cues, it still remains something of a mystery as to how they sense the magnetic field. It’s been suggested that birds sense magnetic values through a light-sensitive molecule called cryptochrome, or through sensory cells containing magnetic iron oxide particles – but definitive evidence for either of these has not yet been provided. </p>
<p>However, behavioural evidence continues to underscore how the Earth’s magnetic field is crucial in helping some birds make their epic journeys to breed each year – providing a global positioning system that might just provide birds with a complete navigational map of the world.</p><img src="https://counter.theconversation.com/content/154992/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Richard Holland receives funding from BBSRC and Leverhulme Trust</span></em></p><p class="fine-print"><em><span>Dmitry Kishkinev received funding from Leverhulme Trust and Russian Science Foundation.</span></em></p>Some birds may effectively possess an in-built, global GPS system.Richard Holland, Professor in Animal Behaviour, School of Natural Sciences, Bangor UniversityDmitry Kishkinev, Lecturer in Animal Behaviour and Behavioural Neuroscience, Keele UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1514222020-12-23T13:41:03Z2020-12-23T13:41:03ZMagnetic induction cooking can cut your kitchen’s carbon footprint<figure><img src="https://images.theconversation.com/files/376248/original/file-20201221-19-2jat4u.jpg?ixlib=rb-1.1.0&rect=15%2C0%2C2101%2C1412&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Bye-bye, burners.</span> <span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/photo/pot-in-modern-kitchen-with-induction-stove-royalty-free-image/501706822?adppopup=true">brizmaker/iStock/Getty Images Plus</a></span></figcaption></figure><p>To curb climate change, many experts have called for <a href="https://www.nytimes.com/interactive/2020/04/19/climate/climate-crash-course-4.html">a massive shift from fossil fuels to electricity</a>. The goal is to electrify processes like heating homes and powering cars, and then generate the increased electrical power needs using low- or zero-carbon sources like wind, solar and hydropower.</p>
<p>More than 30 cities in California, including <a href="https://www.sfchronicle.com/bayarea/article/Berkeley-becomes-first-U-S-city-to-ban-natural-14102242.php">Berkeley</a> and <a href="https://www.sfchronicle.com/bayarea/article/No-more-natural-gas-in-new-San-Francisco-15717658.php">San Francisco</a>, have moved in this direction by banning natural gas service in most new buildings. Currently energy use in buildings generates <a href="https://sfgov.org/scorecards/environment/greenhouse-gas-emissions">over 40% of San Francisco’s greenhouse gas emissions</a>. </p>
<p>There are straightforward electric options for heating buildings and hot water and drying clothes, but going electric could be more controversial in the kitchen. Traditional electric stoves are notoriously slow to heat up and cool down. They also pose safety issues because their heating coils can stay hot for tens of minutes after they are shut off.</p>
<p>What is a serious cook to do? One high-tech alternative is magnetic induction. This technology was first proposed over 100 years ago and <a href="http://www.historyofmicrowave.com/microwave-history/history-of-induction-cooker/">demonstrated at the 1933 Chicago World’s Fair</a>. Today magnetic induction stoves and cooktops are common in Europe and Asia, but remain <a href="https://www.nytimes.com/wirecutter/blog/why-dont-people-use-induction-cooktops/">a niche technology in the U.S.</a> As <a href="https://www.forbes.com/sites/energyinnovation/2019/07/22/as-cities-begin-banning-natural-gas-states-must-embrace-building-electrification-with-smart-policy/?sh=2a54e4166ce6">more cities and states move toward electrification</a>, here’s a look at how magnetic induction works and its pros and cons for cooking. </p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/glH71fM9Oe4?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">Electrical Engineer Bill Kornrumpf describes how magnetic induction cooking works.</span></figcaption>
</figure>
<h2>Heating without a flame</h2>
<p>I am an <a href="https://scholar.google.com/citations?user=VcXxSfkAAAAJ&hl=en">electrical engineer specializing in electromagnetic field research</a>. Much of my work focuses on medical therapy applications – but whether you are exposing human tissue or a pan on a cooktop to electromagnetic fields, the principles are the same.</p>
<p>To understand what electromagnetic fields are, the key principle is that an electric charge creates a field around it – essentially, a force that extends in all directions. Think of static electricity, which is an electric charge often produced by friction. If you rub a balloon on your hair, the friction will charge the balloon with static electric charge; then when you lift the balloon away from your head your hair will rise, even if the balloon isn’t touching it. The balloon is pulling on your hair with an attractive electric force.</p>
<p>Moving electric charges, like electricity flowing through wire, produce magnetic fields – zones of magnetic force around the current’s path. The Earth has a magnetic field because electric currents are flowing in its molten core.</p>
<p>Magnetic fields can also produce electric fields and this is why we use the term electromagnetic fields. This concept was discovered in the 1830s by <a href="https://www.britannica.com/biography/Michael-Faraday">English scientist Michael Faraday</a>, who showed that if an electrically conductive material, such as a wire, is placed in a moving magnetic field, an electric field is created in the conductor. We call this magnetic induction. If the conductor is formed into a loop, an electric current will flow around the loop. </p>
<p>Faraday’s discovery formed the basis for the <a href="https://nationalmaglab.org/education/magnet-academy/watch-play/interactive/faraday-motor">development of electric motors</a>. His work also demonstrated a way to heat materials without using a traditional heat source such as fire.</p>
<p><div data-react-class="Tweet" data-react-props="{"tweetId":"1337517515820306432"}"></div></p>
<h2>Where does the heat come from?</h2>
<p>All materials have resistance, which means that when electric current flows through them, the flow will be <a href="https://www.physicsclassroom.com/class/circuits/Lesson-3/Resistance">hindered at least somewhat</a>. This resistance causes some of the electric energy to be lost: The energy turns into heat, and as a result the conductor warms up. In my biomedical research we investigate using radio frequency magnetic fields to heat up tissues in the body to <a href="https://www.accessdata.fda.gov/scripts/cdrh/cfdocs/cfcfr/CFRSearch.cfm?fr=890.5290">help the tissue heal</a>. </p>
<p>Instead of conventional burners, the cooking spots on induction cooktops are called hobs, and consist of wire coils embedded in the cooktop’s surface. For maximum efficiency, engineers want as much as possible of the magnetic field energy produced by each hob to be absorbed by the cookware sitting on it. The magnetic field will create an electric field in the bottom of the cookware, and because of resistance the pan will heat up, even though the hob does not.</p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/376269/original/file-20201221-21-1oewx6z.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Diagram showing how magnetic induction cooking works." src="https://images.theconversation.com/files/376269/original/file-20201221-21-1oewx6z.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/376269/original/file-20201221-21-1oewx6z.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=466&fit=crop&dpr=1 600w, https://images.theconversation.com/files/376269/original/file-20201221-21-1oewx6z.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=466&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/376269/original/file-20201221-21-1oewx6z.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=466&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/376269/original/file-20201221-21-1oewx6z.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=586&fit=crop&dpr=1 754w, https://images.theconversation.com/files/376269/original/file-20201221-21-1oewx6z.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=586&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/376269/original/file-20201221-21-1oewx6z.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=586&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Magnetic coils below the cooktop’s ceramic glass surface generate a magnetic field that sends pulses directly to the cookware. These magnetic pulses are what heat the cookware.</span>
<span class="attribution"><a class="source" href="https://www.sanjoseca.gov/your-government/departments-offices/environmental-services/climate-smart-san-jos/induction-cooktop-checkout-program">City of San Jose</a></span>
</figcaption>
</figure>
<p>For the best performance, magnetic induction stoves and cooktops need to operate at a high magnetic field frequency – typically, 24KHz. They also require pots made from materials that magnetic fields do not readily pass through. Metals with high iron or nickel content absorb magnetic fields, so they are the most efficient options for induction cooking. Iron absorbs magnetic fields more readily than nickel and is far less expensive, so iron-based materials are most commonly used for magnetic induction cookware.</p>
<h2>More responsive and safer, but more expensive</h2>
<p>Since induction cooktops require something to absorb magnetic fields in order to produce heat, they are intrinsically safer than a traditional electric cooktop. Placing your hand on the hob will not heat up your hand to any noticeable extent. And since these systems heat cookware without directly heating the hob, the hobs cool quickly after the cookware is removed, which reduces the risk of burns.</p>
<p>The cookware itself tends to warm up and cool down quickly, and temperature control is very accurate – one of the key properties that cooks value in gas stoves. Another plus is that induction cooktops commonly have smooth surfaces – often glass or ceramic – so they are easy to clean. </p>
<p>Modern induction cooktops are as energy-efficient as traditional electric stoves and about twice as efficient as gas stoves. But this does not necessarily mean they are less expensive to operate. In many parts of the U.S. <a href="https://www.consumeraffairs.com/homeowners/gas-vs-electric-appliances.html">natural gas is far cheaper than electricity</a>, sometimes by a factor of three or four. This partly explains broader acceptance of induction cooktops in Europe, where until recently natural gas was much more expensive than electricity. </p>
<p><iframe id="aSuM3" class="tc-infographic-datawrapper" src="https://datawrapper.dwcdn.net/aSuM3/1/" height="400px" width="100%" style="border: none" frameborder="0"></iframe></p>
<p>Another factor that has influenced adoption is that induction stoves and cooktops typically <a href="https://www.nytimes.com/wirecutter/blog/why-dont-people-use-induction-cooktops/">cost more than traditional gas or electric stoves</a>, although not substantially so. And cooks will have to replace aluminum, copper, nonmagnetic stainless steel and ceramic pots, none of which work effectively on induction cooktops. One quick check is that if a magnet sticks to the bottom of a pot, the pot will work on an induction cooktop.</p>
<p>[<em>The Conversation’s science, health and technology editors pick their favorite stories.</em> <a href="https://theconversation.com/us/newsletters/science-editors-picks-71/?utm_source=TCUS&utm_medium=inline-link&utm_campaign=newsletter-text&utm_content=science-favorite">Weekly on Wednesdays</a>.]</p>
<p>Despite these factors, I expect that natural gas use reduction ordinances will lead to greatly expanded use of magnetic induction stoves and cooktops. These measures typically focus on newly constructed buildings, so they will not require <a href="https://www.greentechmedia.com/articles/read/whole-home-electrification-electricity-is-cheap-so-why-stop-at-net-zero">expensive conversions of existing homes</a>. </p>
<p>Young singles and families who move into these new residences may not yet have acquired a lot of cookware, and are likely to appreciate the safety associated with magnetic induction, especially if they have children. And early adopters who are willing to pay more for electricity from green sources, or for a hybrid or electric car, may not be upset about paying a few hundred dollars more for a magnetic induction cooktop and pans that work with it.</p>
<p>At the national level, the U.S. may <a href="https://eelp.law.harvard.edu/2020/11/president-elect-biden-supports-a-carbon-enforcement-mechanism-could-that-mean-a-price-on-carbon/">adopt some form of carbon pricing</a> in the near future, which would raise the cost of natural gas. And there is also growing concern about <a href="https://coeh.ph.ucla.edu/effects-residential-gas-appliances-indoor-and-outdoor-air-quality-and-public-health-california">indoor air pollution from gas appliances</a>. More than a century after it was first proposed, magnetic induction cooking’s day in the sun may have arrived.</p><img src="https://counter.theconversation.com/content/151422/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Kenneth McLeod does not work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>Shifting from fossil fuels to electricity is climate-friendly, but serious cooks don’t think much of electric stoves. Will induction cooking finally catch on as an alternative?Kenneth McLeod, Professor of Systems Science, and Director, Clinical Science and Engineering Research Laboratory, Binghamton University, State University of New YorkLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1484042020-11-02T20:01:34Z2020-11-02T20:01:34ZMagnetism of Himalayan rocks reveals the mountains’ complex tectonic history<figure><img src="https://images.theconversation.com/files/365671/original/file-20201026-17-199ct3j.jpg?ixlib=rb-1.1.0&rect=155%2C0%2C2993%2C1999&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Himalayan rocks hold magnetic clues about their origins.</span> <span class="attribution"><span class="source">Craig Robert Martin</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span></figcaption></figure><p>Breathing quickly in the thin mountain air, my colleagues and I set down our equipment. We’re at the base of a jagged outcrop that protrudes upwards out of a steep gravel slope.</p>
<p>The muffled soundscape of the spectacular Himalayan wilderness is punctuated by a military convoy roaring along the Khardung-La road below. It’s a reminder how close we are to the long-disputed borders between India, Pakistan and China which lie on the ridgelines just a few miles away.</p>
<iframe src="https://www.google.com/maps/embed?pb=!1m18!1m12!1m3!1d13088582.506864522!2d68.70515675564154!3d34.45999998049693!2m3!1f0!2f0!3f0!3m2!1i1024!2i768!4f13.1!3m3!1m2!1s0x0%3A0x0!2zMzTCsDI3JzM2LjAiTiA3N8KwNDAnMTIuMCJF!5e1!3m2!1sen!2sus!4v1604077003054!5m2!1sen!2sus" width="100%" height="450" frameborder="0" style="border:0;" allowfullscreen="" aria-hidden="false" tabindex="0"></iframe>
<p>This area also contains a different type of boundary, a narrow sinuous geological structure that stretches along the length of the Himalayan mountain range. Known as a suture zone, it’s only a few kilometers wide and consists of slivers of different types of rocks all sliced together by fault zones. It marks the boundary where two tectonic plates fused together and an ancient ocean disappeared.</p>
<p>Our team of geologists traveled here to collect rocks that erupted as lava more than 60 million years ago. By decoding the magnetic records preserved inside them, we hoped to reconstruct the geography of ancient landmasses – and <a href="https://doi.org/10.1073/pnas.2009039117">revise the story of the creation of the Himalayas</a>.</p>
<h2>Sliding plates, growing mountains</h2>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/366741/original/file-20201030-23-t6znxn.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="artist's rendering of two tectonic plates colliding at a subduction zone" src="https://images.theconversation.com/files/366741/original/file-20201030-23-t6znxn.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/366741/original/file-20201030-23-t6znxn.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=489&fit=crop&dpr=1 600w, https://images.theconversation.com/files/366741/original/file-20201030-23-t6znxn.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=489&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/366741/original/file-20201030-23-t6znxn.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=489&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/366741/original/file-20201030-23-t6znxn.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=614&fit=crop&dpr=1 754w, https://images.theconversation.com/files/366741/original/file-20201030-23-t6znxn.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=614&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/366741/original/file-20201030-23-t6znxn.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=614&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">At a subduction zone, two tectonic plates collide, with one slowly sliding beneath the other.</span>
<span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/illustration/tectonic-plates-world-map-royalty-free-illustration/889618718">VectorMine/iStock via Getty Images Plus</a></span>
</figcaption>
</figure>
<p>Tectonic plates make up the surface of Earth, and they’re constantly in motion – drifting at the <a href="https://www.sciencedirect.com/topics/earth-and-planetary-sciences/tectonic-plate">imperceptibly slow pace</a> of just a few centimeters each year. Oceanic plates are colder and denser than the mantle beneath them, so they sink downward into it at subduction zones.</p>
<p>The sinking edge of the ocean plate drags the ocean floor along behind it like a conveyor belt, pulling the continents toward each other. When the entire ocean plate disappears into <a href="https://www.nationalgeographic.org/encyclopedia/mantle/">the mantle</a>, the continents on either side plow into each other with enough force to uplift great mountain belts, like the Himalayas.</p>
<p>Geologists generally thought that the Himalayas formed <a href="https://doi.org/10.1130/0016-7606(2000)112%3C324:TOTHAS%3E2.0.CO;2">55 million years ago in a single continental collision</a> – when the Neotethys Ocean plate subducted under the southern edge of Eurasia and the Indian and Eurasian tectonic plates collided. </p>
<p>But by measuring the magnetism of rocks from northwest India’s remote and mountainous Ladakh region, our team has shown that the tectonic collision that formed the world’s largest mountain range was actually a complex, multi-stage process involving at least two subduction zones.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/366500/original/file-20201029-13-1784e5k.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="diagram of interior of Earth and magnetic field stretching from pole to pole" src="https://images.theconversation.com/files/366500/original/file-20201029-13-1784e5k.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/366500/original/file-20201029-13-1784e5k.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=646&fit=crop&dpr=1 600w, https://images.theconversation.com/files/366500/original/file-20201029-13-1784e5k.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=646&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/366500/original/file-20201029-13-1784e5k.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=646&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/366500/original/file-20201029-13-1784e5k.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=811&fit=crop&dpr=1 754w, https://images.theconversation.com/files/366500/original/file-20201029-13-1784e5k.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=811&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/366500/original/file-20201029-13-1784e5k.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=811&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Earth’s magnetic field is generated by movement within the planet’s outer core. Magnetic north and south drift and sometimes flip over time.</span>
<span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/illustration/earth-magnetic-field-scientific-vector-royalty-free-illustration/932342344">VectorMine/iStock via Getty Images Plus</a></span>
</figcaption>
</figure>
<h2>Magnetic messages, preserved for all time</h2>
<p>Constant movement of our planet’s metallic outer core creates electric currents which in turn generate <a href="https://cosmosmagazine.com/geoscience/what-creates-earth-s-magnetic-field/">Earth’s magnetic field</a>. It’s oriented differently depending where in the world you are. The magnetic field always points toward the magnetic north or the south, which is why your compass works, and averaged over thousands of years it points toward the geographic pole. But it also slopes downward into the ground at an angle which varies depending on how far you are from the equator. </p>
<p>When lava erupts and cools to form rock, the magnetic minerals inside lock in the direction of the magnetic field of that location. So <a href="https://doi.org/10.1016/B0-12-369396-9/00106-4">by measuring the magnetization of volcanic rocks</a>, <a href="https://scholar.google.com/citations?hl=en&user=aD8WioMAAAAJ">scientists like me</a> can determine what latitude they came from. Essentially, this method allows us to unwind millions of years of plate tectonic motions and create maps of the world at different times throughout geologic history.</p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/365226/original/file-20201023-20-172l0hn.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Member of our research team collecting samples in Ladakh." src="https://images.theconversation.com/files/365226/original/file-20201023-20-172l0hn.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/365226/original/file-20201023-20-172l0hn.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=884&fit=crop&dpr=1 600w, https://images.theconversation.com/files/365226/original/file-20201023-20-172l0hn.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=884&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/365226/original/file-20201023-20-172l0hn.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=884&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/365226/original/file-20201023-20-172l0hn.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=1111&fit=crop&dpr=1 754w, https://images.theconversation.com/files/365226/original/file-20201023-20-172l0hn.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=1111&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/365226/original/file-20201023-20-172l0hn.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=1111&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Geologist collects core samples using a water-cooled electric core drill.</span>
<span class="attribution"><span class="source">Craig Robert Martin</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<p>Over multiple expeditions to the Ladakh Himalayas, our team collected hundreds of 1-inch diameter rock core samples. These rocks originally formed on a volcano active between 66 and 61 million years ago, around the time that the first stages of collision began. We used a hand-held electric drill with a specially designed diamond coring bit to drill approximately 10 centimeters down into the bedrock. We then carefully marked these cylindrical cores with their original orientation before chiseling them out of the rock with nonmagnetic tools.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/366238/original/file-20201028-15-ujjeor.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="cylindrical rock core samples with markings" src="https://images.theconversation.com/files/366238/original/file-20201028-15-ujjeor.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/366238/original/file-20201028-15-ujjeor.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=431&fit=crop&dpr=1 600w, https://images.theconversation.com/files/366238/original/file-20201028-15-ujjeor.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=431&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/366238/original/file-20201028-15-ujjeor.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=431&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/366238/original/file-20201028-15-ujjeor.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=542&fit=crop&dpr=1 754w, https://images.theconversation.com/files/366238/original/file-20201028-15-ujjeor.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=542&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/366238/original/file-20201028-15-ujjeor.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=542&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">A few rock core samples, with the sample orientation line marked on their sides.</span>
<span class="attribution"><span class="source">Craig Robert Martin</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<p>The aim was to reconstruct where these rocks originally formed, before they were sandwiched between India and Eurasia and uplifted into the high Himalayas. Keeping track of the orientation of the samples as well as the rock layers they came from is essential to calculating which way the ancient magnetic field pointed relative to the surface of the ground as it was over 60 million years ago.</p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/365268/original/file-20201023-19-1igxsu8.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="View of magnetometer equipment at MIT." src="https://images.theconversation.com/files/365268/original/file-20201023-19-1igxsu8.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/365268/original/file-20201023-19-1igxsu8.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=800&fit=crop&dpr=1 600w, https://images.theconversation.com/files/365268/original/file-20201023-19-1igxsu8.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=800&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/365268/original/file-20201023-19-1igxsu8.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=800&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/365268/original/file-20201023-19-1igxsu8.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=1005&fit=crop&dpr=1 754w, https://images.theconversation.com/files/365268/original/file-20201023-19-1igxsu8.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=1005&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/365268/original/file-20201023-19-1igxsu8.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=1005&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The magnetometer sits inside a magnetically shielded room at the MIT Paleomagnetism Laboratory.</span>
<span class="attribution"><span class="source">Craig Robert Martin</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<p>We brought our samples back to the <a href="http://www.benweiss.mit.edu/">MIT Paleomagnetism Laboratory</a> and, inside a special room that’s shielded from the modern-day magnetic field, we heated them in increments up to 1,256 degrees Fahrenheit (680 degrees Celsius) to slowly remove the magnetization.</p>
<p>Different mineral populations acquire their magnetization at different temperatures. Incrementally heating and then measuring the samples in this way enables us to extract the original magnetic direction by removing more recent overprints that might hide it.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/366244/original/file-20201028-17-hpwmb7.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="diagrams depicting India colliding with Eurasia either in a single stage or multiple stages" src="https://images.theconversation.com/files/366244/original/file-20201028-17-hpwmb7.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/366244/original/file-20201028-17-hpwmb7.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=239&fit=crop&dpr=1 600w, https://images.theconversation.com/files/366244/original/file-20201028-17-hpwmb7.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=239&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/366244/original/file-20201028-17-hpwmb7.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=239&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/366244/original/file-20201028-17-hpwmb7.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=301&fit=crop&dpr=1 754w, https://images.theconversation.com/files/366244/original/file-20201028-17-hpwmb7.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=301&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/366244/original/file-20201028-17-hpwmb7.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=301&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Black lines mark boundaries between tectonic plates. Black lines with triangular tick marks show subduction zones, with the direction of subduction. The Trans-Tethyan Subduction Zone is the additional subduction zone not accounted for in the single-stage collision model. The Trans-Tethyan Subduction Zone is where the volcanic island chain formed before the Indian continent collided into it and pushed it into Eurasia, forming the Himalaya.</span>
<span class="attribution"><a class="source" href="https://doi.org/10.1073/pnas.2009039117">Martin et al 'Paleocene latitude of the Kohistan-Ladakh arc indicates multi-stage India-Eurasia collision,' PNAS 2020</a>, <a class="license" href="http://creativecommons.org/licenses/by-nc-sa/4.0/">CC BY-NC-SA</a></span>
</figcaption>
</figure>
<h2>Magnetic traces build a map</h2>
<p>Using the average magnetic direction of the whole suite of samples we can calculate their ancient latitude, which we refer to as the paleolatitude.</p>
<p>The original single-stage collision model for the Himalaya predicts that these rocks would have formed close to Eurasia at a latitude of around 20 degrees north, but our data shows that these rocks did not form on either the Indian or the Eurasian continents. Instead, they formed on a chain of volcanic islands, out in the open Neotethys Ocean at a latitude of about 8 degrees north, thousands of kilometers south of where Eurasia was located at the time.</p>
<p>This finding can be explained only if there were <a href="https://doi.org/10.1038/ngeo2418">two subduction zones</a> pulling India rapidly toward Eurasia, rather than just one. </p>
<p>[<em>You’re smart and curious about the world. So are The Conversation’s authors and editors.</em> <a href="https://theconversation.com/us/newsletters/weekly-highlights-61?utm_source=TCUS&utm_medium=inline-link&utm_campaign=newsletter-text&utm_content=weeklysmart">You can get our highlights each weekend</a>.]</p>
<p>During a geologic time period known as the Paleocene, India caught up with the volcanic island chain and collided with it, scraping up the rocks we eventually sampled onto the northern edge of India. India then continued northward before <a href="https://doi.org/10.1016/j.epsl.2013.01.023">ramming into Eurasia around 40 to 45 million years ago</a> – 10 to 15 million years later than was generally thought.</p>
<p>This final continental collision raised the volcanic islands from sea level up over 4,000 meters to their present-day location, where they form jagged outcrops along a spectacular Himalayan mountain pass.</p><img src="https://counter.theconversation.com/content/148404/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Craig Robert Martin receives funding from the National Science Foundation (NSF).</span></em></p>Earth’s magnetic field locks information into lava as it cools into rock. Millions of years later, scientists can decipher this magnetic data to build geologic timelines and maps.Craig Robert Martin, Ph.D. Student in Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology (MIT)Licensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1481112020-10-15T11:38:47Z2020-10-15T11:38:47ZLife on Earth: why we may have the Moon’s now defunct magnetic field to thank for it<figure><img src="https://images.theconversation.com/files/363663/original/file-20201015-19-16azo0e.jpg?ixlib=rb-1.1.0&rect=44%2C36%2C4928%2C3238&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Photo of a nearly full Moon shining brightly on the Earth's atmosphere, taken from the International Space Station.</span> <span class="attribution"><span class="source">NASA</span></span></figcaption></figure><p>The habitability of a planet depends on many factors. One is the existence of a strong and long-lived magnetic field. These fields are generated thousands of kilometres below the planet’s surface in its liquid core and extend far into space – shielding the atmosphere from harmful solar radiation.</p>
<p>Without a strong magnetic field, a planet struggles to hang on to a breathable atmosphere – which is bad news for life as we know it. A new study, <a href="https://advances.sciencemag.org/lookup/doi/10.1126/sciadv.abc0865">published in Science Advances</a>, suggests that the Moon’s now extinct magnetic field may have helped protect our planet’s atmosphere as life was forming around 4 billion years ago.</p>
<p>Today, Earth has a strong global magnetic field <a href="https://theconversation.com/earths-magnetic-field-may-change-faster-than-we-thought-new-research-142752">that protects the atmosphere</a> and low-orbiting satellites from harsh solar radiation. In contrast, the Moon does not possess either a breathable atmosphere or a global magnetic field.</p>
<p>Global magnetic fields are generated by the motion of molten iron in the cores of planets and moons. Keeping the fluid moving requires energy, such as heat trapped within the core. When there is insufficient energy, the field dies.</p>
<p>Without a global magnetic field, the charged particles of the solar wind (radiation from the Sun) passing close to a planet generate electric fields that can accelerate charged atoms, known as ions, out of the atmosphere. This process is <a href="https://theconversation.com/how-did-mars-lose-its-habitable-climate-the-answer-is-blowing-in-the-solar-wind-50258">happening today</a> on Mars and it is losing oxygen as a result – something that has been directly measured by the <a href="https://mars.nasa.gov/maven/">Mars atmosphere and volatile evolution (Maven) mission</a>. The solar wind can also collide with the atmosphere and knock molecules into space. </p>
<p>The Maven team estimates that the amount of oxygen lost from the Martian atmosphere throughout its history <a href="https://www.sciencedirect.com/science/article/abs/pii/S0019103517306917">is equivalent</a> to that contained in a global layer of water, 23 metres thick.</p>
<h2>Probing ancient magnetic fields</h2>
<p>The new research investigates how the Earth’s and Moon’s early fields may have interacted. But probing these ancient fields isn’t easy. Scientists rely on ancient rocks that contain small grains that got magnetised as the rocks formed, saving the direction and strength of the magnetic field at that time and place. Such rocks are rare and extracting their magnetic signal requires <a href="https://theconversation.com/are-the-earths-magnetic-poles-about-to-swap-places-strange-anomaly-gives-reassuring-clue-142859">careful and delicate laboratory measurement</a>. </p>
<figure class="align-center ">
<img alt="A picture of the ancient moon with magnetic field lines." src="https://images.theconversation.com/files/363444/original/file-20201014-21-b9ysdx.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/363444/original/file-20201014-21-b9ysdx.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=338&fit=crop&dpr=1 600w, https://images.theconversation.com/files/363444/original/file-20201014-21-b9ysdx.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=338&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/363444/original/file-20201014-21-b9ysdx.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=338&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/363444/original/file-20201014-21-b9ysdx.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=424&fit=crop&dpr=1 754w, https://images.theconversation.com/files/363444/original/file-20201014-21-b9ysdx.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=424&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/363444/original/file-20201014-21-b9ysdx.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=424&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Our Moon, four billion years ago generated its own magnetic field.</span>
<span class="attribution"><span class="source">NASA</span></span>
</figcaption>
</figure>
<p>Such studies have, however, unveiled that Earth has generated a magnetic field for at least <a href="https://pubmed.ncbi.nlm.nih.gov/20203044/">the last 3.5 billion years</a>, and possibly <a href="https://pubmed.ncbi.nlm.nih.gov/26228145/">as far back as 4.2 billion years</a>, with a mean strength <a href="https://www.nature.com/articles/s41561-018-0288-0?proof=t">just over half</a> of the present-day value. We don’t know much about how the field was behaving any earlier than that. </p>
<p>By contrast, the Moon’s field was perhaps even stronger than Earth’s around 4 billion years ago, before <a href="https://pubmed.ncbi.nlm.nih.gov/25477467/">precipitously declining</a> to a weak field state by 3.2 billion years ago. At present, little is known about the structure or time-variability of these ancient fields, though.</p>
<p>Another complexity is the interaction between the early lunar and geomagnetic fields. The new paper, which modelled the interaction of two magnetic fields with north poles either aligned or opposite, shows that the interaction extends the region of near-Earth space between our planet and the Sun that is shielded from the solar wind. </p>
<p>The new study is an interesting first step towards understanding how important such effects would be when averaged over a lunar orbit or the hundreds of millions of years that are important for assessing planetary habitability. But to know for sure we need further modelling and more measurements of the strengths of the Earth and Moon’s early magnetic fields.</p>
<p>What’s more, a strong magnetic field does not guarantee the continued habitability of a planet’s atmosphere – its surface and deep interior environments matter too, as do influences from space. For example, the brightness and activity of the Sun <a href="https://theconversation.com/mission-to-the-sun-will-protect-us-from-devastating-solar-storms-and-help-us-travel-deeper-into-space-78583">has evolved</a> over billions of years and so has the ability of the solar wind to strip atmospheres.</p>
<p>How each of these factors contributes to the evolution of planetary habitability, and hence life, is still not fully understood. Their nature and how they interact with each other are also likely to change over geological timescales. But thankfully, the latest study has added another piece to an already fascinating puzzle.</p><img src="https://counter.theconversation.com/content/148111/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>The authors do not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and have disclosed no relevant affiliations beyond their academic appointment.</span></em></p>The Earth’s magnetic field was most likely weaker when life evolved on our planet than it is today.Christopher Davies, Associate Professor in Theoretical Geophysics, University of LeedsJon Mound, Associate Professor of Geophysics, University of LeedsLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1428592020-07-20T19:05:55Z2020-07-20T19:05:55ZAre the Earth’s magnetic poles about to swap places? Strange anomaly gives reassuring clue<figure><img src="https://images.theconversation.com/files/347987/original/file-20200716-35-1nbg7fm.jpg?ixlib=rb-1.1.0&rect=0%2C0%2C5540%2C3741&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">St Helena, where Earth's magnetic field behaves strangely.</span> <span class="attribution"><span class="source">Umomos/Shutterstock</span></span></figcaption></figure><p>Deep inside the Earth, liquid iron is flowing and generating the Earth’s magnetic field, which protects our atmosphere and satellites against harmful radiation from the Sun. This field changes over time, and also behaves differently in different parts of the world. The field can even change polarity completely, with the magnetic north and south poles switching places. This is called <a href="https://theconversation.com/the-earths-magnetic-field-reverses-more-often-now-we-know-why-96957">a reversal</a> and last happened 780,000 years ago.</p>
<p>Between South America and southern Africa, there is an enigmatic magnetic region called the South Atlantic Anomaly, where the field is a lot weaker than we would expect. Weak and unstable fields are thought to precede magnetic reversals, so some have argued this feature may be evidence that we are <a href="https://www.frontiersin.org/articles/10.3389/feart.2016.00040/full">facing one</a>. </p>
<p>Now our new study, published in the <a href="https://www.pnas.org/cgi/doi/10.1073/pnas.2001217117">Proceedings of the National Academy of Sciences</a>, has uncovered how long the field in the South Atlantic has been acting up – and sheds light on whether it is something to worry about. </p>
<p>Weak magnetic fields make us more prone to magnetic storms that have the potential to knock out electronic infrastructure, including power grids. The magnetic field of the South Atlantic Anomaly is already so weak that it can adversely affect satellites and their technology when they fly past it.
The strange region is thought to be related to a patch of magnetic field that is pointing a different direction to the rest at the top of the planet’s liquid outer core at a depth of 2,889 kilometres within the Earth. </p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/348476/original/file-20200720-18366-1l7lzae.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/348476/original/file-20200720-18366-1l7lzae.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=334&fit=crop&dpr=1 600w, https://images.theconversation.com/files/348476/original/file-20200720-18366-1l7lzae.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=334&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/348476/original/file-20200720-18366-1l7lzae.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=334&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/348476/original/file-20200720-18366-1l7lzae.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=420&fit=crop&dpr=1 754w, https://images.theconversation.com/files/348476/original/file-20200720-18366-1l7lzae.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=420&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/348476/original/file-20200720-18366-1l7lzae.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=420&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">The geomagnetic field at Earth’s surface with the South Atlantic Anomaly shaded in darkest blue and St Helena marked with a star. The black outline shows the limits of a large region of anomalously slow seismic velocity (implying hot mantle) sitting just on top of Earth’s core. Colours range from weak fields (blue) to strong fields (yellow).</span>
<span class="attribution"><span class="source">Richard K. Bono</span>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>This “<a href="https://science.sciencemag.org/content/312/5775/900">reverse flux patch</a>” itself has grown over the last 250 years. But we don’t know whether it is simply a one off product of the chaotic motions of the outer core fluid or rather the latest in a series of anomalies within this particular region over long time frames. </p>
<p>If it is a non-recurring feature, then its current location is not significant – it could happen anywhere, perhaps randomly. But if this is the case, the question of whether its increasing size and depth could mark the start of a new reversal remains.</p>
<p>If it is the latest in a string of features reoccurring over millions of years, however, then this would make a reversal less likely. But it would require a specific explanation for what was causing the magnetic field to act strangely in this particular place. </p>
<h2>Volcanic rocks</h2>
<p>To find out, we travelled to Saint Helena – an island in the middle of the South Atlantic Ocean. This island, where Napoleon was exiled to and eventually died in 1821, is made of volcanic rocks. These originate from two separate volcanoes and were erupted from between eight million and 11.5 million years ago. </p>
<figure class="align-right ">
<img alt="" src="https://images.theconversation.com/files/347981/original/file-20200716-29-gkblfw.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/347981/original/file-20200716-29-gkblfw.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=795&fit=crop&dpr=1 600w, https://images.theconversation.com/files/347981/original/file-20200716-29-gkblfw.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=795&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/347981/original/file-20200716-29-gkblfw.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=795&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/347981/original/file-20200716-29-gkblfw.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=999&fit=crop&dpr=1 754w, https://images.theconversation.com/files/347981/original/file-20200716-29-gkblfw.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=999&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/347981/original/file-20200716-29-gkblfw.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=999&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Lead author Yael Engbers is drilling a core on Saint Helena.</span>
<span class="attribution"><span class="source">Andy Biggin</span>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>When volcanic rocks cool down, small grains of iron-oxide in them get magnetised and therefore save the direction and strength of the Earth’s magnetic field at that time and place. We collected some of those rocks and brought them back to our lab in Liverpool, where we carried out experiments to find out what the magnetic field was like at the time of eruption. </p>
<p>Our results showed us that the field at Saint Helena had very different directions throughout the time of eruption, suggesting that the field in this region was much less stable than in other places. It therefore challenges the idea that the abnormality has only been around for a few centuries. Instead, the whole region has likely been unstable on a timescale of millions of years. This implies the current situation is not as rare as some scientists had assumed, making it less likely that it represents the start of a reversal.</p>
<h2>A window into Earth’s interior</h2>
<p>So what could explain the odd magnetic region? The liquid outer core that is generating it moves (by <a href="https://www.bbc.co.uk/bitesize/guides/zttrd2p/revision/2">convection</a>) at such high speeds that changes can occur on very short, human timescales. The outer core interacts with a layer called the mantle on top of it, which moves far slower. That means the mantle is unlikely to have changed very much in the last ten million years. </p>
<figure class="align-center ">
<img alt="Picture of the Earth's inner structure." src="https://images.theconversation.com/files/348381/original/file-20200720-37-1ko1mab.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/348381/original/file-20200720-37-1ko1mab.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=371&fit=crop&dpr=1 600w, https://images.theconversation.com/files/348381/original/file-20200720-37-1ko1mab.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=371&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/348381/original/file-20200720-37-1ko1mab.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=371&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/348381/original/file-20200720-37-1ko1mab.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=466&fit=crop&dpr=1 754w, https://images.theconversation.com/files/348381/original/file-20200720-37-1ko1mab.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=466&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/348381/original/file-20200720-37-1ko1mab.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=466&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Earth’s inner structure.</span>
<span class="attribution"><span class="source">wikipedia</span>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<p>From <a href="https://www.bgs.ac.uk/discoveringGeology/hazards/earthquakes/seismicWaves.html">seismic waves</a> passing through the Earth, we have some insight into the structure of the mantle. Underneath Africa there is a <a href="https://www.nature.com/articles/ngeo2733">large feature</a> in the lowermost mantle where the waves move extra slow through the Earth – meaning there’s most likely an unusually warm region of the lowermost mantle. This possibly causes a different interaction with the outer core at that specific location, which could <a href="https://www.nature.com/articles/ncomms8865">explain</a> the strange behaviour of the magnetic field in the South Atlantic. </p>
<p>Another aspect of the inside of the Earth is the inner core, which is a solid ball the size of Pluto beneath the outer core. This solid feature is slowly growing, but not at the same rate everywhere. There is a possibility that it is growing faster on one side, causing a flow inside the outer core that is reaching the outer boundary with the rocky mantle just under the <a href="https://www.nature.com/articles/nature12574?proof=true">Atlantic hemisphere</a>. This may be causing irregular behaviour of the magnetic field on the long timescales we found on Saint Helena.</p>
<p>Although there are still many questions about the exact cause of the irregular behaviour in the South Atlantic, this study shows us that it has been around for millions of years and is most likely a result of geophysical interactions in the Earth’s mysterious interior.</p><img src="https://counter.theconversation.com/content/142859/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Yael Annemiek Engbers receives funding from The Leverhulme Trust.</span></em></p><p class="fine-print"><em><span>Andrew Biggin receives funding from The Leverhulme Trust and the Natural Environment Research Council.</span></em></p>The Earth’s magnetic field is a lot weaker than we would expect around the island of St Helena.Yael Annemiek Engbers, PhD candidate, University of LiverpoolAndrew Biggin, Professor of Palaeomagnetism, University of LiverpoolLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1427522020-07-20T11:52:47Z2020-07-20T11:52:47ZEarth’s magnetic field may change faster than we thought – new research<figure><img src="https://images.theconversation.com/files/348116/original/file-20200717-33-1cc38wb.jpg?ixlib=rb-1.1.0&rect=47%2C61%2C4475%2C2420&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">It's long been a mystery how fast the Earth's magnetic field changes.</span> <span class="attribution"><a class="source" href="https://www.shutterstock.com/image-illustration/abstract-earth-magnetic-fields-250125172">Andrey VP/Shutterstock</a></span></figcaption></figure><p>The Earth’s magnetic field, generated 3,000km below our feet in the liquid iron core, is crucially important to life on our planet. It extends out into space, wrapping us in an electromagnetic blanket that shields the atmosphere and satellites from solar radiation.</p>
<p>Yet the magnetic field is <a href="https://theconversation.com/the-earths-magnetic-north-pole-is-shifting-rapidly-so-what-will-happen-to-the-northern-lights-117237">constantly changing</a> in both its strength and direction and has undergone some dramatic shifts in the past. This includes <a href="https://theconversation.com/why-the-earths-magnetic-poles-could-be-about-to-swap-places-and-how-it-would-affect-us-71910">enigmatic reversals of the magnetic poles</a>, with the south pole becoming the north pole and vice versa. </p>
<p>A long-standing question has been how fast the field can change. Our new study, <a href="https://www.nature.com/articles/s41467-020-16888-0">published in Nature Communications</a>, has uncovered some answers.</p>
<p>Rapid changes of the magnetic field are of great interest because they represent the most extreme behaviour of the ocean of molten iron in the liquid core. By tying the observed changes to core processes, we can learn important information about an otherwise inaccessible region of our planet. </p>
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Read more:
<a href="https://theconversation.com/why-the-earths-magnetic-poles-could-be-about-to-swap-places-and-how-it-would-affect-us-71910">Why the Earth's magnetic poles could be about to swap places – and how it would affect us</a>
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<p>Historically, the fastest changes in Earth’s magnetic field have been <a href="https://theconversation.com/the-earths-magnetic-field-reverses-more-often-now-we-know-why-96957">associated with reversals</a>, which occur at irregular intervals a few times every million years. But we discovered field changes that are much faster and more recent than any of the data associated with actual reversals. </p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/154274/original/image-20170125-23872-mjgami.gif?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/154274/original/image-20170125-23872-mjgami.gif?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=328&fit=crop&dpr=1 600w, https://images.theconversation.com/files/154274/original/image-20170125-23872-mjgami.gif?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=328&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/154274/original/image-20170125-23872-mjgami.gif?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=328&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/154274/original/image-20170125-23872-mjgami.gif?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=412&fit=crop&dpr=1 754w, https://images.theconversation.com/files/154274/original/image-20170125-23872-mjgami.gif?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=412&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/154274/original/image-20170125-23872-mjgami.gif?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=412&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Magnetic reversal.</span>
<span class="attribution"><span class="source">NASA.</span></span>
</figcaption>
</figure>
<p>Nowadays satellites help monitor changes in the field in both space and time, complemented by navigational records and ground-based observatories. This information reveals that changes in the modern field are rather ponderous, around a tenth of a degree per year. But, while we know that the field has existed <a href="https://science.sciencemag.org/content/327/5970/1238.abstract?casa_token=QREHDyVnFUUAAAAA:tHfGEiP4L3NrRO-TnbT73JpMhjiNdZXqZDMAuW6RyhdJO9NMBMVdJUBSl6dpvBvasC-uNGzTaGuEYJA">for at least 3.5 billion years</a>, we don’t know much about its behaviour prior to 400 years ago. </p>
<p>To track the ancient field, scientists analyse the magnetism recorded by sediments, lava flows and human-made artefacts. That’s because these materials contain microscopic magnetic grains that record the signature of Earth’s field at the time they cooled (for lavas) or were added to the landmass (for sediments). Sediment records from central Italy around the time of the last polarity reversal almost 800,000 years ago <a href="https://academic.oup.com/gji/article/199/2/1110/618671">suggest relatively rapid field changes</a> reaching one degree per year.</p>
<p>Such measurements, however, are extremely challenging, with results <a href="https://academic.oup.com/gji/article-abstract/213/3/1744/4944226?redirectedFrom=fulltext">still being debated</a>. For example, there are uncertainties in the process by which sediments acquire their magnetism. </p>
<h2>Improved measurements</h2>
<p>Our research takes a different approach by using computer models based on the physics of the field generation process. This is combined with a recently published reconstruction of global variations in Earth’s magnetic field spanning the last 100,000 years, based on a compilation of measurements from sediments, lavas and artefacts. </p>
<p>This shows that changes in the direction of Earth’s magnetic field reached rates that are up to ten degrees per year – ten times larger than the fastest currently reported variations. </p>
<p>The fastest observed changes in the geomagnetic field direction occurred around 39,000 years ago. This shift was associated with a locally weak field in a confined region just off the west coast of central America. The event followed the global “<a href="https://www.sciencedirect.com/science/article/abs/pii/S0012821X12003421">Laschamp excursion</a>” – a “failed reversal” of the Earth’s magnetic field around 41,000 years ago in which the magnetic poles briefly moved far from the geographic poles before returning. </p>
<p>The fastest changes appear to be associated with local weakening of the magnetic field. Our model suggests this is caused by movement of patches of intense magnetic field across the surface of the liquid core. These patches are more prevalent at lower latitudes, suggesting that future searches for rapid changes in direction should focus on these areas.</p>
<h2>The impact on society</h2>
<p>Changes in the magnetic field, such as reversals, probably don’t pose a threat to life. Humans did manage to live through the dramatic Laschamp excursion. Today, the threat is mainly down to our reliance on electronic infrastructure. Space weather events such as geomagnetic storms, arising from the interaction between the magnetic field and incoming solar radiation, could disrupt satellite communications, GPS and power grids. </p>
<figure class="align-center ">
<img alt="Picture of a satellite orbiting Earth." src="https://images.theconversation.com/files/348119/original/file-20200717-19-6qkfuv.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/348119/original/file-20200717-19-6qkfuv.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/348119/original/file-20200717-19-6qkfuv.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/348119/original/file-20200717-19-6qkfuv.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/348119/original/file-20200717-19-6qkfuv.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/348119/original/file-20200717-19-6qkfuv.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/348119/original/file-20200717-19-6qkfuv.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Satellites are at risk from space weather.</span>
<span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/space-satellite-orbiting-earth-elements-this-363654452">Andrey Armyagov/Shutterstock</a></span>
</figcaption>
</figure>
<p>This is troubling – the economic cost of a collapse of the US power grid due to a space-weather event <a href="https://www.swpc.noaa.gov/content/space-weather-faq-frequently-asked-questions">has been estimated at</a> around one trillion dollars. The threat is serious enough for space weather to appear as a <a href="https://www.gov.uk/government/collections/national-risk-register-of-civil-emergencies">high priority</a> on the UK national risk register. </p>
<p>Space weather events tend to be more prevalent in regions where the magnetic field is weak – something we know can happen when the field is changing rapidly. Unfortunately, computer simulations suggest that directional changes arise after the field strength begins to weaken, meaning we cannot predict dips in field strength by just monitoring the field direction. Future work using more advanced simulations can shed more light on this issue. </p>
<p>Is another rapid change in the magnetic field on its way? This is very hard to answer. The fastest changes are also the rarest events: for example, the changes identified around the Laschamp excursion are over two times faster than any other changes occurring over the last 100,000 years. </p>
<p>This makes it difficult for scientists to predict rapid changes – they are “black swan events” that come as a surprise and have a big impact. One possible route forward is to use physics-based models of how the field behaves as part of the forecast. </p>
<p>We still have a lot to learn about the “speed limit” of Earth’s magnetic field. Rapid changes have not yet been directly observed during a polarity reversal, but they should be expected since the field is thought to become globally weak at these times.</p><img src="https://counter.theconversation.com/content/142752/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Christopher Davies receives funding from NERC. </span></em></p>Changes in the Earth’s magnetic field pose a great risk to electronic infrastructure.Christopher Davies, Associate professor, University of LeedsLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1232652019-09-16T20:35:31Z2019-09-16T20:35:31ZExplainer: what happens when magnetic north and true north align?<figure><img src="https://images.theconversation.com/files/292338/original/file-20190913-190002-1sm4kgi.jpg?ixlib=rb-1.1.0&rect=42%2C16%2C5615%2C3638&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Very rarely, depending on where you are in the world, your compass can actually point to true north.
</span> <span class="attribution"><a class="source" href="https://www.shutterstock.com/download/confirm/1393250468?src=vKUFR7i2pguMpY8BD0TNHg-1-62&size=huge_jpg">https://www.shutterstock.com</a></span></figcaption></figure><p>At some point in recent weeks, a once-in-a-lifetime event happened for people at Greenwich in the United Kingdom.</p>
<p>Magnetic compasses at the historic London area, known as the <a href="https://www.rmg.co.uk/discover/explore/prime-meridian-greenwich">home of the Prime Meridian</a>, were said to have pointed directly at the north geographic pole for the <a href="https://www.sciencealert.com/compasses-are-about-to-do-something-that-hasn-t-happened-in-over-300-years">first time in 360 years</a>. </p>
<p>This means that, for someone at Greenwich, magnetic north (the direction in which a compass needle points) would have been in exact alignment with geographic north. </p>
<p>Geographic north (also called “true north”) is the direction towards the fixed point we call the North Pole. </p>
<p>Magnetic north is the direction towards the north magnetic pole, which is a wandering point where the Earth’s magnetic field goes vertically down into the planet. </p>
<p>The north magnetic pole is currently about 400km south of the north geographic pole, but can move to about 1,000km away.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/292137/original/file-20190912-190065-q685ai.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/292137/original/file-20190912-190065-q685ai.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/292137/original/file-20190912-190065-q685ai.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=515&fit=crop&dpr=1 600w, https://images.theconversation.com/files/292137/original/file-20190912-190065-q685ai.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=515&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/292137/original/file-20190912-190065-q685ai.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=515&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/292137/original/file-20190912-190065-q685ai.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=648&fit=crop&dpr=1 754w, https://images.theconversation.com/files/292137/original/file-20190912-190065-q685ai.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=648&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/292137/original/file-20190912-190065-q685ai.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=648&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The lines of the Earth’s magnetic field come vertically out of the Earth at the south magnetic pole and go vertically down into the Earth at the north magnetic pole.</span>
<span class="attribution"><span class="source">Nasky/Shutterstock</span></span>
</figcaption>
</figure>
<h2>How do the norths align?</h2>
<p>Magnetic north and geographic north align when the so-called “angle of declination”, the difference between the two norths at a particular location, is 0°. </p>
<p>Declination is the angle in the horizontal plane between magnetic north and geographic north. It changes with time and geographic location.</p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/292139/original/file-20190912-190021-lr3y1f.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/292139/original/file-20190912-190021-lr3y1f.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/292139/original/file-20190912-190021-lr3y1f.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=402&fit=crop&dpr=1 600w, https://images.theconversation.com/files/292139/original/file-20190912-190021-lr3y1f.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=402&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/292139/original/file-20190912-190021-lr3y1f.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=402&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/292139/original/file-20190912-190021-lr3y1f.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=505&fit=crop&dpr=1 754w, https://images.theconversation.com/files/292139/original/file-20190912-190021-lr3y1f.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=505&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/292139/original/file-20190912-190021-lr3y1f.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=505&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The declination angle varies between -90° and +90°.</span>
<span class="attribution"><span class="source">Author provided</span></span>
</figcaption>
</figure>
<p>On a map of the Earth, lines along which there is zero declination are called agonic lines. Agonic lines follow variable paths depending on time variation in the Earth’s magnetic field.</p>
<p>Currently, zero declination is occurring in some parts of Western Australia, and will likely move westward in coming years.</p>
<p>That said, it’s hard to predict exactly when an area will have zero declination. This is because the rate of change is slow and current models of the Earth’s magnetic field only cover a few years, and are updated at roughly five-year intervals. </p>
<p>At some locations, alignment between magnetic north and geographic north is very unlikely at any time, based on predictions.</p>
<h2>The ever-changing magnetic poles</h2>
<p>Most compasses point towards Earth’s north magnetic pole, which is usually in a different place to the north geographic pole. The location of the magnetic poles is constantly changing.</p>
<p>Earth’s magnetic poles exist because of its magnetic field, which is produced by electric currents in the liquid part of its core. This magnetic field is defined by intensity and two angles, inclination and declination.</p>
<p>The relationship between geographic location and declination is something people using magnetic compasses have to consider. Declination is the reason a compass reading for north in one location is different to a reading for north in another, especially if there is considerable distance between both locations.</p>
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<strong>
Read more:
<a href="https://theconversation.com/new-evidence-for-a-human-magnetic-sense-that-lets-your-brain-detect-the-earths-magnetic-field-113536">New evidence for a human magnetic sense that lets your brain detect the Earth's magnetic field</a>
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<p>Bush walkers have to be mindful of declination. In Perth, declination is currently close to 0° but in eastern Australia it can be up to 12°. This difference can be significant. If a bush walker following a magnetic compass disregards the local value of declination, they may walk in the wrong direction.</p>
<p>The polarity of Earth’s magnetic poles has also changed over time and has undergone <a href="https://www.nasa.gov/topics/earth/features/2012-poleReversal.html">pole reversals</a>. This was significant as we learnt more about plate tectonics in the 1960s, because it <a href="https://divediscover.whoi.edu/mid-ocean-ridges/magnetics-polarity/">linked the idea</a> of seafloor spreading from mid-ocean ridges to magnetic pole reversals. </p>
<h2>Geographic north</h2>
<p>Geographic north, perhaps the more straightforward of the two, is the direction that points straight at the North Pole from any location on Earth. </p>
<p>When flying an aircraft from A to B, we use directions based on geographic north. This is because we have accurate geographic locations for places and need to follow precise routes between them, usually trying to minimise fuel use by taking the shortest route. All GPS navigation uses geographic location.</p>
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<strong>
Read more:
<a href="https://theconversation.com/five-maps-that-will-change-how-you-see-the-world-74967">Five maps that will change how you see the world</a>
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<p>Geographic coordinates, latitude and longitude, are defined relative to Earth’s <a href="https://www.scientificamerican.com/article/earth-is-not-round/">spheroidal</a> shape. The geographic poles are at latitudes of 90°N (North Pole) and 90°S (South Pole), whereas the Equator is at 0°.</p>
<h2>An alignment at Greenwich</h2>
<p>For hundreds of years, declination at Greenwich was negative, meaning compass needles were pointing west of true north.</p>
<p>At the time of writing this article I used an <a href="https://ngdc.noaa.gov/geomag/calculators/magcalc.shtml#declination">online calculator</a> to discover that, at the Greenwich Observatory, the Earth’s magnetic field currently has a declination just above zero, about +0.011°. </p>
<p>The average rate of change in the area is about 0.19° per year, which at Greenwich’s latitude represents about 20km per year. This means next year, locations about 20km west of Greenwich will have zero declination.</p>
<p>It’s impossible to say how long compasses at Greenwich will now point east of true north. </p>
<p>Regardless, an alignment after 360 years at the home of the Prime Meridian is undoubtedly a once-in-a-lifetime occurrence.</p><img src="https://counter.theconversation.com/content/123265/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Paul Wilkes does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>Recently, magnetic compasses at Greenwich pointed directly at true north for the first time in 360 years. This is currently happening in Western Australia too. But what does it mean?Paul Wilkes, Senior Research Geophysicist, CSIROLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1172372019-05-20T10:18:45Z2019-05-20T10:18:45ZThe Earth’s magnetic north pole is shifting rapidly – so what will happen to the northern lights?<figure><img src="https://images.theconversation.com/files/275022/original/file-20190516-69204-7vunsn.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Northern lights in Lake Lappajärvi, Finland.</span> <span class="attribution"><span class="source">Santeri Viinamäki</span>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span></figcaption></figure><p>Like most planets in our solar system, the Earth has its own magnetic field. Thanks to its <a href="https://theconversation.com/curious-kids-what-would-happen-if-the-earths-core-went-cold-107537">largely molten iron core</a>, our planet is in fact a bit like a bar magnet. It has a north and south magnetic pole, separate from the geographic poles, with a field connecting the two. This field protects our planet from radiation and is responsible for creating the northern and southern lights – spectacular events that are only visible near the magnetic poles.</p>
<p>However, with reports that the magnetic north pole has started moving swiftly at 50km per year – and may soon be over Siberia – it has long been unclear whether the northern lights will move too. Now a new study, <a href="https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2019GL082159">published in Geophysical Research Letters</a>, has come up with an answer. </p>
<p>Our planetary magnetic field has many advantages. For over 2,000 years, travellers <a href="http://www.historyofcompass.com/compass-history/invention-of-the-compass/">have been able to use</a> it to navigate across the globe. <a href="https://theconversation.com/migrating-birds-use-a-magnetic-map-to-travel-long-distances-82624">Some animals</a> even seem to be able to find their way thanks to the magnetic field. But, more importantly than that, our geomagnetic field helps <a href="https://theconversation.com/how-did-mars-lose-its-habitable-climate-the-answer-is-blowing-in-the-solar-wind-50258">protect all life on Earth</a>. </p>
<p>Earth’s magnetic field extends hundreds of thousands of kilometres out from the centre of our planet – stretching right out into interplanetary space, forming what scientists call a “<a href="https://theconversation.com/weve-discovered-the-worlds-largest-drum-and-its-in-space-111465">magnetosphere</a>”. This magnetosphere helps to deflect solar radiation and cosmic rays, preventing the destruction of our atmosphere. This protective magnetic bubble isn’t perfect though, and some solar matter and energy can transfer into our magnetosphere. As it is then funnelled into the poles by the field, it results in the spectacular displays of the <a href="https://theconversation.com/what-caused-those-spectacular-northern-lights-and-how-you-can-catch-them-next-time-39081">northern lights</a>. </p>
<h2>A wandering pole</h2>
<p>Since Earth’s magnetic field is created by its moving, molten iron core, its poles aren’t stationary and they wander independently of one another. In fact, since its first formal discovery in 1831, the north magnetic pole has travelled over 2,000km from the Boothia Peninsula in the far north of Canada to high in the Arctic Sea. This wandering has generally been quite slow, around 9km a year, allowing scientists to easily keep track of its position. But since the turn of the century, this speed has increased to <a href="https://www.nature.com/articles/d41586-019-00007-1">50km a year</a>. The south magnetic pole is also moving, though at a much slower rate (10-15km a year).</p>
<p>This rapid wandering of the north magnetic pole has caused some problems for scientists and navigators alike. Computer models of where the north magnetic pole might be in the future have become seriously outdated, making accurate compass-based navigation difficult. Although GPS does work, it can <a href="https://mycoordinates.org/challenges-for-positioning-and-navigation-in-the-arctic/">sometimes be unreliable</a> in the polar regions. In fact, the pole is moving so quickly that scientists responsible for mapping the Earth’s magnetic field were recently <a href="https://www.ncei.noaa.gov/news/world-magnetic-model-out-cycle-release">forced to update</a> their model much earlier than expected.</p>
<h2>Will the aurora move?</h2>
<p>The <a href="https://theconversation.com/what-caused-those-spectacular-northern-lights-and-how-you-can-catch-them-next-time-39081">aurora</a> generally form in an oval about the magnetic poles, and so if those poles move, it stands to reason that the aurora might too. With predictions suggesting that the north pole will soon be approaching northern Siberia, what effect might that have on the aurora?</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/curious-kids-what-causes-the-northern-lights-111573">Curious Kids: what causes the northern lights?</a>
</strong>
</em>
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<p>The northern lights are currently mostly visible from northern Europe, Canada and the northern US. If, however, they shifted north, across the geographic pole, following the north magnetic pole, then that could well change. Instead, the northern lights would become more visible from Siberia and northern Russia and less visible from the much more densely populated US/Canadian border.</p>
<p>Fortunately, for those aurora hunters in the northern hemisphere, it seems as though this might not actually be the case. <a href="https://agupubs.onlinelibrary.wiley.com/doi/epdf/10.1029/2019GL082159">A recent study</a> made a computer model of the aurora and the Earth’s magnetic poles based on data dating back to 1965. It showed that rather than following the magnetic poles, the aurora follows the “<a href="http://wdc.kugi.kyoto-u.ac.jp/poles/polesexp.html">geomagnetic poles</a>” instead. There’s only a small difference between these two types of poles –- but it’s an important one. </p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/275021/original/file-20190516-69189-feozze.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/275021/original/file-20190516-69189-feozze.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=605&fit=crop&dpr=1 600w, https://images.theconversation.com/files/275021/original/file-20190516-69189-feozze.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=605&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/275021/original/file-20190516-69189-feozze.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=605&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/275021/original/file-20190516-69189-feozze.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=761&fit=crop&dpr=1 754w, https://images.theconversation.com/files/275021/original/file-20190516-69189-feozze.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=761&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/275021/original/file-20190516-69189-feozze.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=761&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Magnetic versus geomagnetic poles.</span>
<span class="attribution"><span class="source">wikipedia.</span>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<p>The magnetic poles are the points on the Earth’s surface where a compass needle points downwards or upwards, vertically. They aren’t necessarily connected and drawing a line between these points, through the Earth, would not necessarily cross its centre. Therefore, to make better models over time, scientists assume that the Earth is like a bar magnet at its centre, creating poles that are exactly opposite each other – “<a href="https://en.wikipedia.org/wiki/Antipodal_point">antipodal</a>”. This means that if we drew a line between these points, the line would cross directly through the Earth’s centre. At the points where that line crosses the Earth’s surface, we have the geomagnetic poles.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/275107/original/file-20190517-69192-1liuaqx.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/275107/original/file-20190517-69192-1liuaqx.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=341&fit=crop&dpr=1 600w, https://images.theconversation.com/files/275107/original/file-20190517-69192-1liuaqx.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=341&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/275107/original/file-20190517-69192-1liuaqx.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=341&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/275107/original/file-20190517-69192-1liuaqx.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=428&fit=crop&dpr=1 754w, https://images.theconversation.com/files/275107/original/file-20190517-69192-1liuaqx.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=428&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/275107/original/file-20190517-69192-1liuaqx.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=428&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Positions of the north magnetic pole (red) and the geomagnetic pole (blue) between 1900 and 2020.</span>
<span class="attribution"><a class="source" href="http://www.geomag.bgs.ac.uk/education/poles.html">British Geological Survey</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<p>The geomagnetic poles are a kind of reliable, averaged out version of the magnetic poles, which move erratically all the time. Because of that, it turns out they aren’t moving anywhere near as fast as the magnetic north pole is. And since the aurora seems to follow the more averaged version of the magnetic field, it means that the northern lights aren’t moving that fast either. It seems as though the aurora are staying where they are – at <a href="https://theconversation.com/dont-panic-the-northern-lights-wont-be-turning-off-anytime-soon-72436">least for now</a>. </p>
<p>We already know that the magnetic pole moves. Both poles have wandered ever since the Earth existed. In fact, the poles even flip over, with north becoming south and south becoming north. These magnetic reversals have occurred throughout history, every 450,000 years or so on average. The last reversal occurred 780,000 years ago meaning we <a href="https://theconversation.com/why-the-earths-magnetic-poles-could-be-about-to-swap-places-and-how-it-would-affect-us-71910">could be due a reversal soon</a>. </p>
<p>So rest assured that a wandering pole, even a fast one, shouldn’t cause too many problems – except for those scientists whose job it is to model it.</p><img src="https://counter.theconversation.com/content/117237/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Nathan Case receives funding from the Science and Technology Facilities Council. </span></em></p>As the Earth’s magnetic north pole heads towards Siberia, concerns have been raised that the northern lights could move with it.Nathan Case, Senior Research Associate in Space and Planetary Physics, Lancaster UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1132052019-05-19T23:51:43Z2019-05-19T23:51:43ZCurious Kids: why do we not use the magnetic energy the Earth provides to create electricity?<figure><img src="https://images.theconversation.com/files/273465/original/file-20190509-183083-okrc69.jpg?ixlib=rb-1.1.0&rect=1%2C3%2C1031%2C688&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">This sounds like a good idea at first, but it's not very practical.</span> <span class="attribution"><a class="source" href="https://www.nasa.gov/image-feature/hello-from-above">Image Credit: NASA/Mark Vande Hei</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span></figcaption></figure><p><em><a href="https://theconversation.com/au/topics/curious-kids-36782">Curious Kids</a> is a series for children. If you have a question you’d like an expert to answer, send it to curiouskids@theconversation.edu.au You might also like the podcast <a href="http://www.abc.net.au/kidslisten/imagine-this/">Imagine This</a>, a co-production between ABC KIDS listen and The Conversation, based on Curious Kids.</em> </p>
<hr>
<blockquote>
<p><strong>Why do we not use the magnetic energy the Earth provides to create electricity? – student of Ms Brown’s Year 5 science class, Neerim South Primary School, Victoria.</strong></p>
</blockquote>
<hr>
<p>Hi!</p>
<p>This sounds like a good idea at first, but it’s not very practical. Before I explain why, let me first explain how we generate electricity in case somebody reading this doesn’t already know.</p>
<p>Electricity (let’s say “electrical current”) is when electrically-charged particles flow, like water in a pipe. There are two kinds of electrical charge – positive and negative. Positive charges attract negative charges, but two particles with the same charge (both positive or both negative) will repel. That means they push apart.</p>
<p>In other words, opposites attract.</p>
<p>Usually, electrical current is made of tiny negative charges called “electrons” which come from atoms.</p>
<p>Everything you can touch is made of atoms. Every atom is surrounded by a cloud of electrons moving randomly like bees around a beehive, attracted to the positive charges in the centre (or “nucleus”) of the atom. </p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/Rz1turGsGow?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
</figure>
<p>An electrical current usually happens when electrons leave their atoms and flow to other atoms. </p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/curious-kids-how-and-why-do-magnets-stick-together-101899">Curious Kids: How and why do magnets stick together?</a>
</strong>
</em>
</p>
<hr>
<h2>How to create an electrical current</h2>
<p>There are three main ways we produce electrical current. </p>
<p>The first is batteries. In batteries, there is an “electrochemical reaction” that causes electrons to move from one kind of atom onto another kind of atom with a stronger attraction to electrons. A battery is designed to force these electrons to pass through a wire into your electronic devices. </p>
<p>A second way is solar cells. Light energy is absorbed by electrons in something called “semiconductors” (usually silicon) which causes electrons to move, creating electrical current.</p>
<p>But I think you’re asking about the third way that is usually used to generate electrical currents for power sockets in your house. </p>
<h2>Spinning a coil of wire in a strong magnetic field</h2>
<p>This third way is to move an electrical wire quickly through a magnetic field. You need to do this because electrons in a wire cannot feel the magnetic force unless they are moving. </p>
<p>To get a enough current for everybody, you must move <em>a lot</em> of wire through a magnetic field. We do this by spinning a coil (containing many loops of wire) quickly in a strong magnetic field. </p>
<p>During each turn of the coil, electrons get a kick from the magnetic field, moving them along. This creates electrical current. In this animation, S represents the “south pole” of the magnet and N represents the “north pole”. The animation only shows a single loop of wire spinning in the magnetic field. In a real generator, there would be hundreds or even thousands of loops.</p>
<iframe src="https://giphy.com/embed/yUMGHOEMfSWVa" width="100%" height="270" frameborder="0" class="giphy-embed" allowfullscreen=""></iframe>
<p><a href="https://giphy.com/gifs/ac-educational-generator-yUMGHOEMfSWVa"></a></p>
<p>Machines that do this are called generators. You can spin the coil using falling water (that’s called “hydroelectricity”), steam (produced from coal, oil, gas, nuclear energy or heat from the Sun), wind turbines that use the wind, and so on.</p>
<p>In most generators, each time the coil does half a turn, electrons get a magnetic kick. In the next half-turn, they get a magnetic kick in the opposite direction. This means the direction of the current keeps swapping through many cycles rapidly. </p>
<p>Electrical current which swaps direction is called “alternating current” or AC for short. Batteries produce current that travels only in one direction, called “direct current” or DC for short.</p>
<p>In generators, we are not taking energy out of the magnetic field. The energy going into electrical current is actually coming from the energy used to spin the coil. Scientists call this “kinetic energy”.</p>
<h2>Back to the Earth’s magnetic field</h2>
<p>Now (finally!) to answer your question: why don’t we use Earth’s magnetic field to generate electricity?</p>
<p>The amount of current a generator produces, depends mostly on at least three things: 1) how many loops of wire in the coil, 2) how fast the coil is spun and 3) how strong the magnetic field is. </p>
<p>Earth’s magnetic field is very weak, so you would get very little current from your generator.</p>
<p>How weak? Have you ever seen those button-shaped neodymium-iron-boron magnets, also called “neo-magnets”? (Be careful, they can really pinch you). </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/273464/original/file-20190509-183083-1pqqxnl.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/273464/original/file-20190509-183083-1pqqxnl.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/273464/original/file-20190509-183083-1pqqxnl.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=427&fit=crop&dpr=1 600w, https://images.theconversation.com/files/273464/original/file-20190509-183083-1pqqxnl.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=427&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/273464/original/file-20190509-183083-1pqqxnl.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=427&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/273464/original/file-20190509-183083-1pqqxnl.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=537&fit=crop&dpr=1 754w, https://images.theconversation.com/files/273464/original/file-20190509-183083-1pqqxnl.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=537&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/273464/original/file-20190509-183083-1pqqxnl.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=537&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">These magnets are small, but powerful.</span>
<span class="attribution"><a class="source" href="https://www.flickr.com/photos/x1brett/5803831883/in/photolist-9QSa1X-7sLCmW-2eiLjFp-QzGQjC-9dbaTE-2cmZyvY-QDQEXL-Pt8hBH-24mmRvD-KBuzF-2aHk3fW-8RVEPi-29axEjS-2cFh5o3-2cyBPpB-TfJxcG-2bWovs7-bx8bin-RL1kT8-NntTrB-5VUeBc-5VUeCR-dh3WdB-a2oeq6-9e2GGH-8Pc7S-Tdnx49-2fmzEwZ-Re8Tie-85GU4M-qbSULK-7sGFnt-egGmNb-Pt8hdg-2asJTfE-2aL5nPd-29qxmV3-egGmYY-2cQksno-7sGD3T-2dto8x1-bjsqAP-RYe3Fq-2fkZYLx-q9AAiN-bar5Q2-fxDHje-2ecjPiw-7sGEut-b3j1yP">Flickr/brett jordan</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<p>They have magnetic fields around 6,000 times stronger than Earth’s magnetic field. Magnetic fields inside electrical generators are similar to this.</p>
<p>Even fridge magnets have magnetic fields approximately 200 times stronger than Earth’s.</p>
<p><em>Update: This article was updated on May 21 to include nuclear energy among the energy sources listed.</em> </p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/curious-kids-why-do-leaves-fall-off-trees-111914">Curious Kids: why do leaves fall off trees?</a>
</strong>
</em>
</p>
<hr>
<p><em>Hello, curious kids! Have you got a question you’d like an expert to answer? Ask an adult to send your question to curiouskids@theconversation.edu.au</em></p>
<figure class="align-left ">
<img alt="" src="https://images.theconversation.com/files/168011/original/file-20170505-21620-huq4lj.png?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/168011/original/file-20170505-21620-huq4lj.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=376&fit=crop&dpr=1 600w, https://images.theconversation.com/files/168011/original/file-20170505-21620-huq4lj.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=376&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/168011/original/file-20170505-21620-huq4lj.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=376&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/168011/original/file-20170505-21620-huq4lj.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=472&fit=crop&dpr=1 754w, https://images.theconversation.com/files/168011/original/file-20170505-21620-huq4lj.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=472&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/168011/original/file-20170505-21620-huq4lj.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=472&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption"></span>
<span class="attribution"><a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<p><em>Please tell us your name, age and which city you live in. We won’t be able to answer every question but we will do our best.</em></p><img src="https://counter.theconversation.com/content/113205/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Stephen G Bosi does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>Even fridge magnets have magnetic fields approximately 200 times stronger than Earth’s.Stephen G Bosi, Senior Lecturer in Physics, University of New EnglandLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1135362019-03-18T17:01:05Z2019-03-18T17:01:05ZNew evidence for a human magnetic sense that lets your brain detect the Earth’s magnetic field<figure><img src="https://images.theconversation.com/files/264258/original/file-20190317-28505-1b1zf7w.jpg?ixlib=rb-1.1.0&rect=17%2C247%2C2849%2C1818&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Do you have a magnetic compass in your head?</span> <span class="attribution"><a class="source" href="https://www.shutterstock.com/image-illustration/moral-compass-career-path-concept-human-115938361">Lightspring/Shutterstock.com</a></span></figcaption></figure><p>Do human beings have a magnetic sense? <a href="https://www.springer.com/us/book/9783642797514">Biologists know</a> <a href="https://doi.org/10.1016/S0959-4388(00)00235-X">other animals do</a>. They think it helps creatures including bees, turtles and birds <a href="https://doi.org/10.1016/S0959-4388(02)00389-6">navigate through the world</a>.</p>
<p>Scientists have tried to investigate whether humans belong on the list of magnetically sensitive organisms. For decades, there’s been a back-and-forth between <a href="https://www.worldcat.org/title/human-navigation-and-the-sixth-sense/oclc/11022691&referer=brief_results">positive reports</a> and <a href="https://www.jstor.org/stable/1685499">failures to demonstrate</a> the trait in people, with <a href="https://www.springer.com/us/book/9781461379928">seemingly endless controversy</a>.</p>
<p>The mixed results in people may be due to the fact that virtually all past studies relied on behavioral decisions from the participants. If human beings do possess a magnetic sense, daily experience suggests that it would be very weak or deeply subconscious. Such faint impressions could easily be misinterpreted – or just plain missed – when trying to make decisions.</p>
<p>So our research group – including a <a href="https://maglab.caltech.edu/">geophysical biologist</a>, a <a href="https://neuro.caltech.edu">cognitive neuroscientist</a> and a <a href="http://www.isp.ac/index_e.html">neuroengineer</a> – took another approach. <a href="https://maglab.caltech.edu/human-magnetic-reception-laboratory/">What we found</a> arguably provides the first concrete neuroscientific <a href="https://doi.org/10.1523/ENEURO.0483-18.2019">evidence that humans do have a geomagnetic sense</a>. </p>
<h2>How does a biological geomagnetic sense work?</h2>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/264257/original/file-20190317-28479-jh5hpf.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/264257/original/file-20190317-28479-jh5hpf.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/264257/original/file-20190317-28479-jh5hpf.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=515&fit=crop&dpr=1 600w, https://images.theconversation.com/files/264257/original/file-20190317-28479-jh5hpf.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=515&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/264257/original/file-20190317-28479-jh5hpf.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=515&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/264257/original/file-20190317-28479-jh5hpf.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=648&fit=crop&dpr=1 754w, https://images.theconversation.com/files/264257/original/file-20190317-28479-jh5hpf.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=648&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/264257/original/file-20190317-28479-jh5hpf.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=648&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Life on Earth is exposed to the planet’s ever-present geomagnetic field that varies in intensity and direction across the planetary surface.</span>
<span class="attribution"><a class="source" href="https://www.shutterstock.com/image-vector/illustration-physics-magnetic-field-that-extends-1165968205">Nasky/Shutterstock.com</a></span>
</figcaption>
</figure>
<p>The Earth is surrounded by a magnetic field, generated by the movement of the planet’s liquid core. It’s why a magnetic compass points north. At Earth’s surface, this magnetic field is fairly weak, <a href="https://nationalmaglab.org/about/maglab-dictionary/tesla">about 100 times weaker</a> than that of a refrigerator magnet.</p>
<p>Over the past 50 years or so, scientists have shown that hundreds of organisms in nearly all branches of the bacterial, <a href="https://www.livescience.com/54242-protists.html">protist</a> and animal kingdoms have the ability to detect and respond to this geomagnetic field. In some animals – <a href="https://doi.org/10.1007/BF00611096">such as honey bees</a> – the geomagnetic behavioral responses are <a href="https://pdfs.semanticscholar.org/750f/ce1b8f4723b09dd2fb1324fc916c9578c77b.pdf">as strong as the responses</a> to light, odor or touch. Biologists have identified strong responses in vertebrates ranging from <a href="https://doi.org/10.1038/37057">fish</a>, <a href="http://jeb.biologists.org/content/205/24/3903.full">amphibians</a>, <a href="https://doi.org/10.1126/science.1064557">reptiles</a>, numerous birds and a diverse variety of mammals including <a href="http://jeb.biologists.org/content/120/1/1.short">whales</a>, <a href="https://doi.org/10.1038/srep09917">rodents</a>, <a href="https://doi.org/10.1371/journal.pone.0001676">bats</a>, <a href="https://doi.org/10.1073/pnas.0803650105">cows</a> and <a href="https://doi.org/10.7717/peerj.6117">dogs</a> – the last of which can be trained to find a hidden bar magnet. In all of these cases, the animals are using the geomagnetic field as components of their homing and navigation abilities, along with other cues like sight, smell and hearing.</p>
<p>Skeptics dismissed early reports of these responses, largely because there didn’t seem to be a biophysical mechanism that could translate the Earth’s weak geomagnetic field into strong neural signals. This view was dramatically changed by the <a href="https://pubs.geoscienceworld.org/gsa/gsabulletin/article-abstract/73/4/435/5435">discovery that living cells</a> have the <a href="https://doi.org/10.1126/science.472725">ability to</a> build nanocrystals of the <a href="https://doi.org/10.1126/science.201.4360.1026">ferromagnetic</a> <a href="http://jeb.biologists.org/content/140/1/35.short">mineral magnetite</a> – basically, tiny iron magnets. Biogenic crystals of magnetite were first seen in the teeth of one group of mollusks, later in <a href="https://doi.org/10.1126/science.170679">bacteria</a>, and then in a variety of other organisms ranging from protists and animals such as insects, fish and mammals, <a href="https://doi.org/10.1073/pnas.89.16.7683">including within tissues of the human brain</a>.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/264240/original/file-20190317-28475-1vhbs80.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/264240/original/file-20190317-28475-1vhbs80.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/264240/original/file-20190317-28475-1vhbs80.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=267&fit=crop&dpr=1 600w, https://images.theconversation.com/files/264240/original/file-20190317-28475-1vhbs80.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=267&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/264240/original/file-20190317-28475-1vhbs80.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=267&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/264240/original/file-20190317-28475-1vhbs80.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=336&fit=crop&dpr=1 754w, https://images.theconversation.com/files/264240/original/file-20190317-28475-1vhbs80.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=336&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/264240/original/file-20190317-28475-1vhbs80.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=336&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Chains of magnetosomes from a sockeye salmon.</span>
<span class="attribution"><span class="source">Mann, Sparks, Walker & Kirschvink, 1988</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<p>Nevertheless, scientists haven’t considered humans to be magnetically sensitive organisms.</p>
<h2>Manipulating the magnetic field</h2>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/264038/original/file-20190314-28479-1665yfc.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/264038/original/file-20190314-28479-1665yfc.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/264038/original/file-20190314-28479-1665yfc.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=596&fit=crop&dpr=1 600w, https://images.theconversation.com/files/264038/original/file-20190314-28479-1665yfc.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=596&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/264038/original/file-20190314-28479-1665yfc.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=596&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/264038/original/file-20190314-28479-1665yfc.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=749&fit=crop&dpr=1 754w, https://images.theconversation.com/files/264038/original/file-20190314-28479-1665yfc.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=749&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/264038/original/file-20190314-28479-1665yfc.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=749&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Schematic drawing of the human magnetoreception test chamber at Caltech.</span>
<span class="attribution"><span class="source">Modified from 'Center of attraction' by C. Bickel (Hand, 2016).</span></span>
</figcaption>
</figure>
<p>In our new study, we asked 34 participants simply to sit in our testing chamber while we directly recorded electrical activity in their brains with electroencephalography (EEG). Our modified <a href="https://science.howstuffworks.com/faraday-cage.htm">Faraday cage</a> included a set of 3-axis coils that let us create controlled magnetic fields of high uniformity via electric current we ran through its wires. Since we live in mid-latitudes of the Northern Hemisphere, the environmental magnetic field in our lab dips downwards to the north at about 60 degrees from horizontal. </p>
<p>In normal life, when someone rotates their head – say, nodding up and down or turning the head from left to right – the direction of the geomagnetic field (which remains constant in space) will shift relative to their skull. This is no surprise to the subject’s brain, as it directed the muscles to move the head in the appropriate fashion in the first place.</p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/264239/original/file-20190317-28492-1jg4d65.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/264239/original/file-20190317-28492-1jg4d65.png?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/264239/original/file-20190317-28492-1jg4d65.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=513&fit=crop&dpr=1 600w, https://images.theconversation.com/files/264239/original/file-20190317-28492-1jg4d65.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=513&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/264239/original/file-20190317-28492-1jg4d65.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=513&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/264239/original/file-20190317-28492-1jg4d65.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=645&fit=crop&dpr=1 754w, https://images.theconversation.com/files/264239/original/file-20190317-28492-1jg4d65.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=645&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/264239/original/file-20190317-28492-1jg4d65.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=645&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Study participants sat in the experimental chamber facing north, while the downwards-pointing field rotated clockwise (blue arrow) from northwest to northeast or counterclockwise (red arrow) from northeast to northwest.</span>
<span class="attribution"><span class="source">Magnetic Field Laboratory, Caltech</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<p>In our experimental chamber, we can move the magnetic field silently relative to the brain, but without the brain having initiated any signal to move the head. This is comparable to situations when your head or trunk is passively rotated by somebody else, or when you’re a passenger in a vehicle which rotates. In those cases, though, your body will still register vestibular signals about its position in space, along with the magnetic field changes – in contrast, our experimental stimulation was only a magnetic field shift. When we shifted the magnetic field in the chamber, our participants did not experience any obvious feelings.</p>
<p>The EEG data, on the other hand, revealed that certain magnetic field rotations could trigger strong and reproducible brain responses. One EEG pattern known from existing research, called alpha-ERD (event-related desynchronization), typically shows up when a person suddenly detects and processes a sensory stimulus. The brains were “concerned” with the unexpected change in the magnetic field direction, and this triggered the alpha-wave reduction. That we saw such alpha-ERD patterns in response to simple magnetic rotations is powerful evidence for human magnetoreception. </p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/6Y4S2eG9BJA?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">Video shows the dramatic, widespread drop in alpha wave amplitude (deep blue color on leftmost head) following counterclockwise rotations. No drop is observed after clockwise rotation or in the fixed condition. <i>Connie Wang, Caltech</i></span></figcaption>
</figure>
<p>Our participants’ brains only responded when the vertical component of the field was pointing downwards at about 60 degrees (while horizontally rotating), as it does naturally here in Pasadena, California. They did not respond to unnatural directions of the magnetic field – such as when it pointed upwards. We suggest the response is tuned to natural stimuli, reflecting a biological mechanism that has been shaped by natural selection.</p>
<p>Other researchers have shown that animals’ brains filter magnetic signals, only responding to those that are environmentally relevant. It makes sense to reject any magnetic signal that is too far away from the natural values because it most likely is from a magnetic anomaly - a lighting strike, or lodestone deposit in the ground, for example. One early report on birds showed that robins stop using the geomagnetic field if the strength is more than about <a href="https://doi.org/10.1126/science.176.4030.62">25 percent different from what they were used to</a>. It’s possible this tendency might be why previous researchers had trouble identifying this magnetic sense – if they <a href="https://doi.org/10.1016/S1388-2457(02)00186-4">cranked up the strength of the magnetic field</a> to “help” subjects detect it, they might have instead ensured that subjects’ brains ignored it.</p>
<p>Moreover, our series of experiments show that the receptor mechanism – the biological magnetometer in human beings – is not electrical induction, and can tell north from south. This latter feature rules out completely the so-called <a href="https://doi.org/10.1146/annurev-biophys-032116-094545">“quantum compass” or “cryptochrome”</a> mechanism which is popular these days in the animal literature on magnetoreception. Our results are consistent only with functional magnetoreceptor cells based on the <a href="https://doi.org/10.1016/0303-2647(81)90060-5">biological magnetite hypothesis</a>. Note that a magnetite-based system <a href="https://doi.org/10.1098/rsif.2009.0491.focus">can also explain</a> <a href="https://doi.org/10.1098/rsif.2009.0435.focus">all of the behavioral effects in birds</a> that promoted the rise of the quantum compass hypothesis.</p>
<h2>Brains register magnetic shifts, subconsciously</h2>
<p>Our participants were all unaware of the magnetic field shifts and their brain responses. They felt that nothing had happened during the whole experiment – they’d just sat alone in dark silence for an hour. Underneath, though, their brains revealed a wide range of differences. Some brains showed almost no reaction, while other brains had alpha waves that shrank to half their normal size after a magnetic field shift.</p>
<p>It remains to be seen what these hidden reactions might mean for human behavioral capabilities. Do the weak and strong brain responses reflect some kind of individual differences in navigational ability? Can those with weaker brain responses benefit from some kind of training? Can those with strong brain responses be trained to actually feel the magnetic field? </p>
<p>A human response to Earth-strength magnetic fields might seem surprising. But given the evidence for magnetic sensation in our animal ancestors, it might be more surprising if humans had completely lost every last piece of the system. Thus far, we’ve found evidence that people have working magnetic sensors sending signals to the brain – a previously unknown sensory ability in the subconscious human mind. The full extent of our magnetic inheritance remains to be discovered.</p><img src="https://counter.theconversation.com/content/113536/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Shinsuke Shimojo received funding from Human Frontier Science Program (HFSP), Japanese Science and Technology Agency (JST), and currently receives funding from DARPA. </span></em></p><p class="fine-print"><em><span>Daw-An Wu receives funding from DARPA. </span></em></p><p class="fine-print"><em><span>Joseph Kirschvink receives funding from the RadioBio program of DARPA, and previous support for this work was from the Human Frontiers Science Program (HFSP).</span></em></p>Your brain’s sensory talents go way beyond those traditional five senses. A team of geoscientists and neurobiologists explored how the human brain monitors and responds to magnetic fields.Shinsuke Shimojo, Gertrude Baltimore Professor of Experimental Psychology, California Institute of TechnologyDaw-An Wu, California Institute of TechnologyJoseph Kirschvink, Nico and Marilyn Van Wingen Professor of Geobiology, California Institute of TechnologyLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1128272019-03-12T10:45:18Z2019-03-12T10:45:18ZOld stone walls record the changing location of magnetic north<figure><img src="https://images.theconversation.com/files/263220/original/file-20190311-86686-98h77f.jpg?ixlib=rb-1.1.0&rect=617%2C12%2C3503%2C2305&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">The orientations of the stone walls that crisscross the Northeastern U.S. can tell a geomagnetic tale as well as a historical one.</span> <span class="attribution"><span class="source">John Delano</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span></figcaption></figure><p>When I was a kid living in southern New Hampshire, my family home was on the site of an abandoned farmstead consisting of massive stone foundations of quarried granite where dwellings once stood. Stone walls snaked throughout the forest. As I explored the deep woods of tall oaks and maples, I wondered about who had built these walls, and why. What stories did these walls contain?</p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/263249/original/file-20190311-86699-45fjwd.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/263249/original/file-20190311-86699-45fjwd.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/263249/original/file-20190311-86699-45fjwd.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=799&fit=crop&dpr=1 600w, https://images.theconversation.com/files/263249/original/file-20190311-86699-45fjwd.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=799&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/263249/original/file-20190311-86699-45fjwd.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=799&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/263249/original/file-20190311-86699-45fjwd.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=1004&fit=crop&dpr=1 754w, https://images.theconversation.com/files/263249/original/file-20190311-86699-45fjwd.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=1004&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/263249/original/file-20190311-86699-45fjwd.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=1004&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">As nature reclaimed farmland, stone walls continued to mark historical boundaries.</span>
<span class="attribution"><span class="source">John Delano</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<p>Decades later, while living in a rural setting in upstate New York and approaching retirement <a href="https://scholar.google.com/citations?user=eUpUocsAAAAJ&hl=en&oi=ao">as a geologist</a>, my long dormant interest was rekindled by treks through the neighboring woods. By now I knew that stone walls in New England and New York are iconic vestiges from a time when farmers, in order to plant crops and graze livestock, needed to clear the land of stones. Tons and tons of granite had been <a href="https://www.earthmagazine.org/article/history-science-and-poetry-new-englands-stone-walls">deposited throughout the region during the last glaciation</a> that ended about 10,000 years ago.</p>
<p>By the late 1800s, <a href="https://books.wwnorton.com/books/detail.aspx?id=4294967847&LangType=1033">nearly 170,000 subsistence farming families</a> had built an <a href="https://www.worldcat.org/title/stone-industries-dimension-stone-crushed-stone-geology-technology-distribution-utilization/oclc/551991">estimated 246,000 miles of stone walls</a> across the Northeast. But by then, the Industrial Revolution had already started to contribute to the widespread abandonment of these farms in the northeastern United States. They <a href="https://www.cambridge.org/us/academic/subjects/history/early-republic-and-antebellum-history/those-who-stayed-behind-rural-society-nineteenth-century-new-england-2nd-edition?format=PB">were overgrown by forests</a> within a few decades.</p>
<p>During my more recent walks through the woods, on a whim I used a hand-held GPS unit to map several miles of stone walls. And that was how I realized that in addition to being part of an American legacy, their locations record a centuries-long <a href="https://doi.org/10.1029/2018JB016655">history of the Earth’s wandering magnetic field</a>.</p>
<h2>Connecting the walls with historical maps</h2>
<p>The complex array of walls that emerged from my GPS readings made no sense to me until I found an old map of my town’s property boundaries at the local historical society. Suddenly I saw that some of the stone walls on my map lay along property lines from 1790. They marked boundaries.</p>
<p>My subsequent searches of church records and decades of the federal census revealed the names of these farm families and details of their lives, including annual yields from their harvests. I started to feel like the stone walls were letting me connect with the long-gone folks who had worked this land.</p>
<p>Now the wheels in my scientist’s mind really started spinning. Did the original land surveys from the 18th and 19th centuries in this part of town still exist? What were the magnetic compass-bearings of those boundaries on the original surveys? </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/263252/original/file-20190311-86707-1aapxwy.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/263252/original/file-20190311-86707-1aapxwy.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/263252/original/file-20190311-86707-1aapxwy.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=363&fit=crop&dpr=1 600w, https://images.theconversation.com/files/263252/original/file-20190311-86707-1aapxwy.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=363&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/263252/original/file-20190311-86707-1aapxwy.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=363&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/263252/original/file-20190311-86707-1aapxwy.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=456&fit=crop&dpr=1 754w, https://images.theconversation.com/files/263252/original/file-20190311-86707-1aapxwy.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=456&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/263252/original/file-20190311-86707-1aapxwy.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=456&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Historical maps and surveys underscore the orderly way plots were divvied up from the landscape in a grid.</span>
<span class="attribution"><a class="source" href="https://www.stoddardnh.org/about-us/pages/charles-peirce-maps-stoddard">Charles Peirce/Stoddard, New Hampshire</a></span>
</figcaption>
</figure>
<p>I knew that the location of <a href="https://www.sciencealert.com/navigation-systems-finally-caught-up-with-the-mysteriously-north-pole-shift">magnetic north drifts over time</a> due to <a href="http://www.physics.org/article-questions.asp?id=64">changes in the Earth’s core</a>. Could I determine its drift using stone walls and the old land surveys? My preliminary map of stone walls and a few historical surveys showed that the approach had potential.</p>
<p>To have any scientific value, though, this work had to encompass much larger areas. I needed a different strategy for finding and mapping stone walls. Luckily I found two troves of useful information. First, the New York State Archives had hundreds of the original land surveys from the 18th and 19th centuries. And secondly, airborne LiDAR (light detection and ranging) images were <a href="https://orthos.dhses.ny.gov">publicly available that could reveal</a> <a href="http://www.granit.unh.edu/resourcelibrary/specialtopics/stonewalls/">stone walls hidden beneath the forest canopy</a> over much larger areas than I could cover on my own by foot.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/263259/original/file-20190311-86686-1cp2owv.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/263259/original/file-20190311-86686-1cp2owv.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/263259/original/file-20190311-86686-1cp2owv.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=426&fit=crop&dpr=1 600w, https://images.theconversation.com/files/263259/original/file-20190311-86686-1cp2owv.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=426&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/263259/original/file-20190311-86686-1cp2owv.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=426&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/263259/original/file-20190311-86686-1cp2owv.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=535&fit=crop&dpr=1 754w, https://images.theconversation.com/files/263259/original/file-20190311-86686-1cp2owv.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=535&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/263259/original/file-20190311-86686-1cp2owv.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=535&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Magnetic north and geographic north aren’t the same – and their difference changes over time.</span>
<span class="attribution"><a class="source" href="https://www.shutterstock.com/image-vector/earth-magnetic-field-geomagnetic-diagram-vector-1177065301">Siberian Art/Shutterstock.com</a></span>
</figcaption>
</figure>
<h2>Tracking magnetic north’s drift over time</h2>
<p>The Earth rotates on its axis once every 24 hours. The location of that spin axis in the Northern Hemisphere is called true north, and <a href="https://doi.org/10.1146/annurev.ea.16.050188.001311">wanders very slowly</a>. The location of true north can be considered stationary, though, on a timescale of a few centuries.</p>
<p>But that’s not where a compass aims when it points north. The location of the north magnetic pole is not only at a different location from true north, but also changes rapidly – currently about one degree per 10 years in New England.</p>
<p>The difference in direction between true north and magnetic north (at a specific time and location on the Earth) is known as the <a href="https://www.ngdc.noaa.gov/geomag/calculators/magcalc.shtml#declination">magnetic declination</a>. Global information about historic variations in magnetic declination is currently based on thousands of <a href="https://doi.org/10.1098/rsta.2000.0569">magnetic compass-bearings recorded in ships’ navigational logs</a> from 1590 onwards. </p>
<p>But now my work on 726 miles of stone walls <a href="https://doi.org/10.1029/2018JB016655">provides an independent check on magnetic declination</a> between 1685 and 1910. </p>
<p>Here’s the logic. When settlers were piling up those stones along the boundaries of their plots, they were using property lines that had been laid out according to the surveyors’ compass readings. Using LiDAR images, the bearings of those stone walls could be determined with respect to true north and compared with the surveyors’ magnetic bearings. The difference is the magnetic declination at the time of the original survey. </p>
<p>For example, the original surveys divided New Hampshire’s Stoddard township into hundreds of lots with boundaries with magnetic compass-bearings of N80 degrees W and N14 degrees E in 1768. As the land was cleared for farming, owners built stone walls along and within those 1768 surveyed boundaries.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/262738/original/file-20190307-82677-1bpfxz3.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/262738/original/file-20190307-82677-1bpfxz3.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/262738/original/file-20190307-82677-1bpfxz3.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=408&fit=crop&dpr=1 600w, https://images.theconversation.com/files/262738/original/file-20190307-82677-1bpfxz3.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=408&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/262738/original/file-20190307-82677-1bpfxz3.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=408&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/262738/original/file-20190307-82677-1bpfxz3.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=513&fit=crop&dpr=1 754w, https://images.theconversation.com/files/262738/original/file-20190307-82677-1bpfxz3.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=513&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/262738/original/file-20190307-82677-1bpfxz3.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=513&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Lidar reveals the stone walls hidden beneath the canopy. Comparing their orientation with true north provides the magnetic declination at this location when boundaries were surveyed in 1768.</span>
<span class="attribution"><a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<p>Now one can compare the bearings of those stone wall-defined boundaries relative to magnetic north and true north today. The difference shows that the magnetic declination at this location in 1768 was 7.6 ± 0.3 degrees W. That’s a good match for scientists’ <a href="https://doi.org/10.1029/2002RG000115">current geophysical model</a>. Since the <a href="https://www.ngdc.noaa.gov/geomag-web/#declination">magnetic declination at this location</a> today is 14.2 degrees W, the direction to magnetic north at this location has moved about 6.6 degrees further west since 1768.</p>
<p>Data from these stone walls strengthen the current geophysical model about the Earth’s magnetic field.</p><img src="https://counter.theconversation.com/content/112827/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Prior to my retirement in late 2016, John Delano received research funding from NASA. No current funding.
John Delano is currently a volunteer interpreter at three sites in Colonial Williamsburg, VA.</span></em></p>Scientific inspiration struck a geologist after many walks through the woods in New York and New England. These ruins hold the secret of where the compass pointed north when they were built centuries ago.John Delano, Distinguished Teaching Professor of Atmospheric and Environmental Sciences, University at Albany, State University of New YorkLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1055642018-12-20T11:34:09Z2018-12-20T11:34:09ZDavid vs. Goliath: What a tiny electron can tell us about the structure of the universe<figure><img src="https://images.theconversation.com/files/247814/original/file-20181128-32230-mojlgr.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">An artist's impression of electrons orbiting the nucleus.</span> <span class="attribution"><a class="source" href="https://www.shutterstock.com/download/success?u=http%3A%2F%2Fdownload.shutterstock.com%2Fgatekeeper%2FW3siZSI6MTU0MzQ1OTQ5MCwiYyI6Il9waG90b19zZXNzaW9uX2lkIiwiZGMiOiJpZGxfMTM0NTU2MjQ4IiwiayI6InBob3RvLzEzNDU1NjI0OC9odWdlLmpwZyIsIm0iOjEsImQiOiJzaHV0dGVyc3RvY2stbWVkaWEifSwia3hoTU15VWRSM21XSEF0UEh2SEZjUGJkdHNFIl0%2Fshutterstock_134556248.jpg&pi=33421636&m=134556248&src=ZLYMmD6NnpDeuys3xFAYMQ-1-32">Roman Sigaev/ Shutterstock.com</a></span></figcaption></figure><p>What is the shape of an electron? If you recall pictures from your high school science books, the answer seems quite clear: an electron is a small ball of negative charge that is smaller than an atom. This, however, is quite far from the truth.</p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/247813/original/file-20181128-32221-536vvw.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/247813/original/file-20181128-32221-536vvw.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/247813/original/file-20181128-32221-536vvw.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=500&fit=crop&dpr=1 600w, https://images.theconversation.com/files/247813/original/file-20181128-32221-536vvw.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=500&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/247813/original/file-20181128-32221-536vvw.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=500&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/247813/original/file-20181128-32221-536vvw.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=628&fit=crop&dpr=1 754w, https://images.theconversation.com/files/247813/original/file-20181128-32221-536vvw.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=628&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/247813/original/file-20181128-32221-536vvw.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=628&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">A simple model of an atom with the nucleus of made of protons, which have a positive charge, and neutrons, which are neutral. The electrons, which have a negative charge, orbit the nucleus.</span>
<span class="attribution"><a class="source" href="https://www.shutterstock.com/image-vector/atom-scientific-poster-atomic-structure-nucleus-1067668175?src=q1VjPFk6YNxYoapF9IhEbA-1-36">Vector FX / Shutterstock.com</a></span>
</figcaption>
</figure>
<p>The <a href="https://en.wikipedia.org/wiki/Electron">electron</a> is commonly known as one of the main components of atoms making up the world around us. It is the electrons surrounding the nucleus of every atom that determine how chemical reactions proceed. Their uses in industry are abundant: from electronics and welding to imaging and advanced particle accelerators. Recently, however, a physics experiment called <a href="https://www.nature.com/articles/s41586-018-0599-8">Advanced Cold Molecule Electron EDM</a> (ACME) put an electron on the center stage of scientific inquiry. The question that the ACME collaboration tried to address was deceptively simple: What is the shape of an electron? </p>
<h2>Classical and quantum shapes?</h2>
<p>As far as physicists currently know, electrons have no internal structure – and thus no shape in the classical meaning of this word. In the modern language of particle physics, which tackles the behavior of objects smaller than an atomic nucleus, the fundamental blocks of matter are continuous fluid-like substances known as “quantum fields” that permeate the whole space around us. In this language, an electron is perceived as a quantum, or a particle, of the “electron field.” Knowing this, does it even make sense to talk about an electron’s shape if we cannot see it directly in a microscope – or any other optical device for that matter?</p>
<p>To answer this question we must adapt our definition of shape so it can be used at incredibly small distances, or in other words, in the realm of quantum physics. Seeing different shapes in our macroscopic world really means detecting, with our eyes, the rays of light bouncing off different objects around us. </p>
<p>Simply put, we define shapes by seeing how objects react when we shine light onto them. While this might be a weird way to think about the shapes, it becomes very useful in the subatomic world of quantum particles. It gives us a way to define an electron’s properties such that they mimic how we describe shapes in the classical world. </p>
<p>What replaces the concept of shape in the micro world? Since light is nothing but a combination of oscillating <a href="https://en.wikipedia.org/wiki/Electric_field">electric</a> and <a href="https://en.wikipedia.org/wiki/Magnetic_field">magnetic</a> fields, it would be useful to define quantum properties of an electron that carry information about how it responds to applied electric and magnetic fields. Let’s do that.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/251346/original/file-20181218-27752-scqxl0.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/251346/original/file-20181218-27752-scqxl0.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/251346/original/file-20181218-27752-scqxl0.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/251346/original/file-20181218-27752-scqxl0.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/251346/original/file-20181218-27752-scqxl0.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/251346/original/file-20181218-27752-scqxl0.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/251346/original/file-20181218-27752-scqxl0.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=566&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">This is the apparatus the physicists used to perform the ACME experiment.</span>
<span class="attribution"><a class="source" href="http://sitn.hms.harvard.edu/flash/2014/looking-closer-the-search-for-the-electron-electric-dipole-moment/">Harvard Department of Physics</a>, <a class="license" href="http://creativecommons.org/licenses/by-nc-sa/4.0/">CC BY-NC-SA</a></span>
</figcaption>
</figure>
<h2>Electrons in electric and magnetic fields</h2>
<p>As an example, consider the simplest property of an electron: its electric charge. It describes the force – and ultimately, the acceleration the electron would experience – if placed in some external electric field. A similar reaction would be expected from a negatively charged marble – hence the “charged ball” analogy of an electron that is in elementary physics books. This property of an electron – its charge – survives in the quantum world. </p>
<p>Likewise, another “surviving” property of an electron is called the magnetic dipole moment. It tells us how an electron would react to a magnetic field. In this respect, an electron behaves just like a tiny bar magnet, trying to orient itself along the direction of the magnetic field. While it is important to remember not to take those analogies too far, they do help us see why physicists are interested in measuring those quantum properties as accurately as possible. </p>
<p>What quantum property describes the electron’s shape? There are, in fact, several of them. The simplest – and the most useful for physicists – is the one called the electric dipole moment, or EDM. </p>
<p>In classical physics, EDM arises when there is a spatial separation of charges. An electrically charged sphere, which has no separation of charges, has an EDM of zero. But imagine a dumbbell whose weights are oppositely charged, with one side positive and the other negative. In the macroscopic world, this dumbbell would have a non-zero electric dipole moment. If the shape of an object reflects the distribution of its electric charge, it would also imply that the object’s shape would have to be different from spherical. Thus, naively, the EDM would quantify the “dumbbellness” of a macroscopic object. </p>
<h2>Electric dipole moment in the quantum world</h2>
<p>The story of EDM, however, is very different in the quantum world. There the vacuum around an electron is not empty and still. Rather it is populated by various subatomic particles zapping into virtual existence for short periods of time. </p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/251291/original/file-20181218-27746-11qy3uf.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/251291/original/file-20181218-27746-11qy3uf.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/251291/original/file-20181218-27746-11qy3uf.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=421&fit=crop&dpr=1 600w, https://images.theconversation.com/files/251291/original/file-20181218-27746-11qy3uf.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=421&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/251291/original/file-20181218-27746-11qy3uf.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=421&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/251291/original/file-20181218-27746-11qy3uf.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=529&fit=crop&dpr=1 754w, https://images.theconversation.com/files/251291/original/file-20181218-27746-11qy3uf.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=529&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/251291/original/file-20181218-27746-11qy3uf.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=529&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The Standard Model of particle physics has correctly predicted all of these particles. If the ACME experiment discovered that the electron had an EDM, it would suggest there were other particles that had not yet been discovered.</span>
<span class="attribution"><a class="source" href="https://www.shutterstock.com/image-illustration/diagram-standard-model-particle-physics-178784918?src=xfhHfcHQIOt6RTTLrx9c2Q-1-4">Designua/Shutterstock.com</a></span>
</figcaption>
</figure>
<p>These virtual particles form a “cloud” around an electron. If we shine light onto the electron, some of the light could bounce off the virtual particles in the cloud instead of the electron itself. </p>
<p>This would change the numerical values of the electron’s charge and magnetic and electric dipole moments. Performing very accurate measurements of those quantum properties would tell us how these elusive virtual particles behave when they interact with the electron and if they alter the electron’s EDM.</p>
<p>Most intriguing, among those virtual particles there could be new, unknown species of particles that we have not yet encountered. To see their effect on the electron’s electric dipole moment, we need to compare the result of the measurement to theoretical predictions of the size of the EDM calculated in the currently accepted theory of the Universe, the <a href="https://theconversation.com/the-standard-model-of-particle-physics-the-absolutely-amazing-theory-of-almost-everything-94700">Standard Model</a>. </p>
<p>So far, the Standard Model accurately described all laboratory measurements that have ever been performed. Yet, it is unable to address many of the most fundamental questions, such as <a href="https://www.scientificamerican.com/article/what-is-antimatter-2002-01-24/">why matter dominates over antimatter throughout the universe</a>. The Standard Model makes a prediction for the electron’s EDM too: it requires it to be so small that ACME would have had no chance of measuring it. But what would have happened if ACME actually detected a non-zero value for the electric dipole moment of the electron? </p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/250724/original/file-20181214-185261-1f3j99w.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/250724/original/file-20181214-185261-1f3j99w.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=424&fit=crop&dpr=1 600w, https://images.theconversation.com/files/250724/original/file-20181214-185261-1f3j99w.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=424&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/250724/original/file-20181214-185261-1f3j99w.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=424&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/250724/original/file-20181214-185261-1f3j99w.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=533&fit=crop&dpr=1 754w, https://images.theconversation.com/files/250724/original/file-20181214-185261-1f3j99w.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=533&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/250724/original/file-20181214-185261-1f3j99w.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=533&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">View of the Large Hadron Collider in its tunnel near Geneva, Switzerland. In the LHC two counter-rotating beams of protons are accelerated and forced to collide, generating various particles.</span>
<span class="attribution"><a class="source" href="http://www.apimages.com/metadata/Index/SWITZERLAND-CERN-LHC-CRYOGENIC-SYSTEM/b3aef1c7c68a4092a95939b1ca9d36ec/13/0">AP Photo/KEYSTONE/Martial Trezzini</a></span>
</figcaption>
</figure>
<h2>Patching the holes in the Standard Model</h2>
<p>Theoretical models have been proposed that fix shortcomings of the Standard Model, predicting the existence of <a href="https://en.wikipedia.org/wiki/Physics_beyond_the_Standard_Model">new heavy particles</a>. These models may fill in the gaps in our understanding of the universe. To verify such models we need to prove the existence of those new heavy particles. This could be done through large experiments, such as those at the international <a href="https://home.cern/science/accelerators/large-hadron-collider">Large Hadron Collider (LHC)</a> by directly producing new particles in high-energy collisions.</p>
<p>Alternatively, we could see how those new particles alter the charge distribution in the “cloud” and their effect on electron’s EDM. Thus, unambiguous observation of electron’s dipole moment in ACME experiment would prove that new particles are in fact present. That was the goal of the ACME experiment.</p>
<p>This is the reason why a <a href="https://www.nature.com/articles/s41586-018-0599-8">recent article in Nature</a> about the electron caught my attention. Theorists like <a href="https://scholar.google.com/citations?user=61U_XlgAAAAJ&hl=en&oi=ao">myself</a> use the results of the measurements of electron’s EDM – along with other measurements of properties of other elementary particles – to help to identify the new particles and make predictions of how they can be better studied. This is done to clarify the role of such particles in our current understanding of the universe. </p>
<p>What should be done to measure the electric dipole moment? We need to find a source of very strong electric field to test an electron’s reaction. One possible source of such fields can be found inside molecules such as thorium monoxide. This is the molecule that ACME used in their experiment. Shining carefully tuned lasers at these molecules, a reading of an electron’s electric dipole moment could be obtained, provided it is not too small. </p>
<p>However, as it turned out, it is. Physicists of the ACME collaboration did not observe the electric dipole moment of an electron – which suggests that its value is too small for their experimental apparatus to detect. This fact has important implications for our understanding of what we could expect from the Large Hadron Collider experiments in the future.</p>
<p>Interestingly, the fact that the ACME collaboration did not observe an EDM actually rules out the existence of heavy new particles that could have been easiest to detect at the LHC. This is a remarkable result for a tabletop-sized experiment that affects both how we would plan direct searches for new particles at the giant Large Hadron Collider, and how we construct theories that describe nature. It is quite amazing that studying something as small as an electron could tell us a lot about the universe.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/UIflReRmynk?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">A short animation describing the physics behind EDM and ACME collaboration’s findings.</span></figcaption>
</figure><img src="https://counter.theconversation.com/content/105564/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Alexey Petrov receives funding from US Department of Energy. </span></em></p>What shape is an electron? The answer, believe it or not, has implications for our understanding of the entire universe, and could reveal whether there are mysterious particles still to be discovered.Alexey A Petrov, Professor of Physics, Wayne State UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1059832018-11-08T03:24:21Z2018-11-08T03:24:21ZBlasts from the past: how massive solar eruptions ‘probably’ detonated dozens of US sea mines<figure><img src="https://images.theconversation.com/files/243813/original/file-20181104-83635-1obzabs.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Solar flares captured on the Sun.</span> <span class="attribution"><a class="source" href="https://www.nasa.gov/content/goddard/sunspot-ar2192-release-x2.0-class-solar-flare-on-oct-26-2014">NASA/SDO</a></span></figcaption></figure><p>An extraordinary account of the impact space weather had on military operations in Vietnam in 1972 was found buried in the US Navy archives, according to a newly published article in <a href="https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2018SW002024">Space Weather</a>.</p>
<p>On August 4, 1972, the crew of a US Task Force 77 aircraft flying near a naval minefield in the waters off Hon La observed 20 to 25 explosions over about 30 seconds. They also witnessed an additional 25 to 30 mud spots in the waters nearby. </p>
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Read more:
<a href="https://theconversation.com/its-never-been-more-important-to-keep-an-eye-on-space-weather-65648">It's never been more important to keep an eye on space weather</a>
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<p><a href="http://www.navweaps.com/Weapons/WAMUS_Mines.php#Vietnam_War_%22Destructor%22_Mines">Destructor sea mines</a> had been deployed here during Operation Pocket Money, a mining campaign launched in 1972 against principal North Vietnamese ports.</p>
<p>There was no obvious reason why the mines should have detonated. But it has now emerged the US Navy soon turned its attention to extreme solar activity at the time as a probable cause.</p>
<p>The more we can understand the impact of such space weather on technology then the better we can be prepared for any future extreme solar activity.</p>
<h2>A solar theory</h2>
<p>As detailed in a now declassified <a href="https://vva.vietnam.ttu.edu/repositories/2/digital_objects/83295">US Navy report</a>, the event sparked an immediate investigation about the potential cause(s) of the random detonations of so many sea mines. </p>
<p>The sea mines deployed had a self-destruct feature. But the minimum self-destruct time on these mines was not for another 30 days, so something else was to blame.</p>
<p>On August 15, 1972, the Commander in Chief of the US Pacific Fleet, Admiral Bernard Clarey, asked about a hypothesis that <a href="https://theconversation.com/massive-sunspots-and-huge-solar-flares-mean-unexpected-space-weather-for-earth-83677">solar activity</a> could have caused the mine detonations. </p>
<p>Many of the mines deployed were <a href="http://www.navweaps.com/index_tech/tech-068.php#Magnetic_Mines">magnetic influence sea mines</a> that were designed to detonate when they detected changes in the magnetic field. </p>
<p>Solar activity was then well known to cause <a href="https://theconversation.com/damaging-electric-currents-in-space-affect-earths-equatorial-region-not-just-the-poles-45073">magnetic field changes</a>, but it wasn’t clear whether or not the Sun could cause these unintentional detonations. </p>
<h2>Solar flares</h2>
<p>Early August in 1972 saw some of the most intense <a href="https://link.springer.com/article/10.1007%2FBF00152736">solar activity</a> ever recorded. </p>
<p>A sunspot region, denoted MR 11976, set off a series of intense <a href="https://www.space.com/11506-space-weather-sunspots-solar-flares-coronal-mass-ejections.html">solar flares</a> (energetic explosions of electromagnetic radiation), coronal mass ejections (eruptions of solar plasma material that typically accompany flares) and clouds of charged particles travelling close to the speed of light. </p>
<p>Those conducting the investigation into the mine incident visited the Space Environment Laboratory at the National Oceanographic and Atmospheric Administration (<a href="https://www.swpc.noaa.gov/">NOAA</a>) near Boulder, Colorado, to speak to space scientists.</p>
<p>One of the scientists at NOAA at the time was the now Emeritus Professor Brian Fraser, from Australia’s <a href="https://www.newcastle.edu.au/research-and-innovation/centre/csp/about-us">Newcastle University</a>, and it’s an event he told me he remembers well: </p>
<blockquote>
<p>I was on my first sabbatical leave at NOAA working with Wallace (Wally) Campbell’s group, and one day in Wally’s office I noticed a group of US Navy brass hat gentlemen and a couple of dark suits.</p>
</blockquote>
<p>Brian said he had later quizzed Wally on what was going on, and Wally explained they were concerned about geomagnetic field changes triggering sea mines laid in Hai Phong, North Vietnam.</p>
<blockquote>
<p>There was no mention whether or not they had exploded but maybe Wally was being coy. And of course it was all probably top secret then.</p>
</blockquote>
<p>The outcome of this investigation, as stated in the declassified US Navy <a href="https://vva.vietnam.ttu.edu/repositories/2/digital_objects/83295">report</a>, detailed “a high degree of probability” that the Destructor mines had been detonated by the August solar storm activity.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/243814/original/file-20181104-83629-171fwbu.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/243814/original/file-20181104-83629-171fwbu.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/243814/original/file-20181104-83629-171fwbu.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=151&fit=crop&dpr=1 600w, https://images.theconversation.com/files/243814/original/file-20181104-83629-171fwbu.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=151&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/243814/original/file-20181104-83629-171fwbu.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=151&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/243814/original/file-20181104-83629-171fwbu.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=189&fit=crop&dpr=1 754w, https://images.theconversation.com/files/243814/original/file-20181104-83629-171fwbu.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=189&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/243814/original/file-20181104-83629-171fwbu.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=189&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Declassified: excerpt from U.S. Navy Report, Mine Warfare Project Office - The Mining of North Vietnam, 8 May 1972 to 14 January 1973.</span>
<span class="attribution"><a class="source" href="https://vva.vietnam.ttu.edu/repositories/2/digital_objects/83295">1070416001, Glenn Helm Collection, The Vietnam Center and Archive, Texas Tech University</a></span>
</figcaption>
</figure>
<h2>Solar interference</h2>
<p>Solar storms <a href="https://www.nasa.gov/mission_pages/sunearth/spaceweather/index.html#q13">cause</a> strong magnetic field fluctuations, which impact large power grid infrastructure, particularly in the high-latitude regions beneath the northern and southern auroras. </p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/GrnGi-q6iWc?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">Solar flares captured by NASA and ESA.</span></figcaption>
</figure>
<p>The storms of early August 1972 were no different. There were numerous reports across North America of <a href="https://ieeexplore.ieee.org/document/4075456">power disruptions</a> and <a href="https://ieeexplore.ieee.org/document/6773728">telegraph line outages</a>. Now that light has been shone on the impact of these events on sea mine operations in 1972, the scientific community has another clear example of space weather impacts on technologies.</p>
<p>The intensity of the early August activity peaked when an <a href="https://www.nasa.gov/mission_pages/sunearth/news/X-class-flares.html">X-class</a> solar flare at 0621 UT August 4, 1972, launched an ultra-fast coronal mass ejection that reached Earth in the record time of 14.6 hours. The solar wind normally takes two to three days to reach Earth. </p>
<p>Scientists think that the previous slower ejections from earlier flares had cleared the path for this fast disturbance, similar to what was observed by the <a href="https://stereo.gsfc.nasa.gov/">STEREO</a> spacecraft in <a href="https://theconversation.com/solar-eruption-could-help-earth-prepare-for-technology-melt-down-18747">July 2012</a>.</p>
<p>It’s the impact of this fast disturbance in the solar wind on the Earth’s magnetosphere that <a href="https://agupubs.onlinelibrary.wiley.com/doi/epdf/10.1029/2018SW002024">probably caused</a> the detonation of the Destructor mines.</p>
<h2>Using the past to predict the future</h2>
<p>The <a href="http://wdc.kugi.kyoto-u.ac.jp/dst_realtime/presentmonth/index.html">Dst index</a>, measured in nano-Tesla (nT), is a typical measure of the disturbance level in the Earth’s magnetic field – the more negative, the more intense the storm. </p>
<p>Some recent extreme solar storms, according to this scale, include the 2015 St Patrick’s Day storm (<a href="http://wdc.kugi.kyoto-u.ac.jp/dst_provisional/201503/index.html">-222 nT</a>) and the 2003 Halloween storm (<a href="http://wdc.kugi.kyoto-u.ac.jp/dst_final/200310/index.html">-383 nT</a>).</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/what-the-weather-is-like-on-a-star-can-help-in-the-search-for-life-56275">What the 'weather' is like on a star can help in the search for life</a>
</strong>
</em>
</p>
<hr>
<p>Interestingly, the extreme activity in August 1972 was far less intense on this scale, only weighing in at <a href="http://wdc.kugi.kyoto-u.ac.jp/dst_final/197208/index.html">-125 nT</a>. </p>
<p>Exactly why this storm reached extreme level on some measures, such as its high speed from the Sun, but not on the typical Dst scale is a topic of significant discussion within the scientific <a href="https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/91GL02783">literature</a>.</p>
<p>Given the complexities of this event, <a href="https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2018SW002024">this new paper</a> lays out a grand challenge to the space weather community to use our modern modelling techniques to reexamine this solar event. Hopefully, understanding these strange events will better prepare us for future solar eruptions.</p><img src="https://counter.theconversation.com/content/105983/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Brett Carter receives funding from the Australian Research Council and the Australian Antarctic Science Program. </span></em></p>When dozens of US mines planted in waters off the Vietnam coast detonated almost simultaneously in 1972, all eyes turned to the Sun for an explanation.Brett Carter, Senior lecturer, RMIT UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/866382017-11-08T10:47:41Z2017-11-08T10:47:41ZMysterious ‘geomagnetic spike’ 3,000 years ago challenges our understanding of the Earth’s interior<figure><img src="https://images.theconversation.com/files/193179/original/file-20171103-26426-11y44sy.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">The Earth has a powerful magnetic field.</span> <span class="attribution"><span class="source">NASA</span></span></figcaption></figure><p>The Earth’s magnetic field, generated some 3,000km below our feet in the liquid iron core, threads through the whole planet and far into space – protecting life and satellites from harmful radiation from the sun. But this shielding effect is far from constant, as the field strength varies significantly in both space and time. </p>
<p>Over the last century, the field strength has changed relatively slowly: the biggest change is a 10% fall in the southern Atlantic, which is still a large enough effect to <a href="https://news.spaceweather.com/new-maps-of-the-south-atlantic-anomaly/">cause electronic problems for satellites</a> that have passed through the region. However, <a href="http://www.sciencedirect.com/science/article/pii/S0012821X16300553">new observations</a> and <a href="https://www.nature.com/articles/ncomms15593">modelling</a> suggest that a much greater change strangely occurred around 1000BC in a much smaller region. </p>
<p>This “geomagnetic spike” offers a potentially profound new insight into the dynamics and evolution of Earth’s hidden interior that is now starting to be uncovered. </p>
<p>So what are geomagnetic spikes and what are the prospects and implications of another one coming along? The geomagnetic spike of 1000BC was <a href="https://www.tau.ac.il/sites/tau.ac.il.en/files/media_server/imported/662/files/2013/08/ShaarETAL11_Timna30_EPSL.pdf">first identified</a> from copper slag heaps located in <a href="https://www.wired.com/2010/12/magnetic-copper-slag/">Jordan and Israel</a>. These were dated from organic material within the slag heaps using radiocarbon dating. </p>
<p>Scientists then investigated the copper using sophisticated laboratory techniques to work out what the Earth’s magnetic field was at the time – relying on the fact that when melted iron cools rapidly, it freezes with a signature of the field at that instant. By taking samples from different layers of the slag heap – with slightly different ages and magnetisation – they could also see how the field strength changed with time. They found that the copper slag had recorded Earth’s magnetic field strength rising and then falling by over 100% in only 30 years.</p>
<p>Unexpectedly high field strengths around 1000BC have also been uncovered in <a href="https://www.sciencedirect.com/science/article/pii/S0012821X1200475X">Turkey</a>, <a href="https://www.pnas.org/content/114/1/39.abstract">China</a> and <a href="http://www.geofisica.unam.mx/LatinmagLetters/LL13-03-SP/A/PA07.pdf">Georgia</a> from a variety of sources. Remarkably, the field strength in <a href="https://www.nature.com/articles/ncomms15593">India, Egypt and Cyprus</a> around the same time was completely normal, indicating that the spike was perhaps only 2,000km wide. Such a rapid change over such a small area marks out the geomagnetic spike as one of the most extreme variations of Earth’s magnetic field ever recorded.</p>
<p>The spike seen in Jordan is the result of a much stronger and narrower magnetic feature that was created in Earth’s liquid core. The process that generated the spike is still shrouded in mystery, though it is likely related to the flow of iron within the core, which drags around the magnetic field as it moves (currents produce magnetic fields). The core is heated from below and cooled from above, so the iron within is thought to undergo vigorous turbulent motion, similar to a strongly heated pan of water. One possibility is that the spike was drawn to the surface of Earth’s core <a href="https://www.nature.com/articles/ncomms15593">by a jet of upward moving iron</a>. </p>
<p>After this, the spike may have moved northwest before merging with other magnetic features near the geographic poles. Alternatively, the spike intensity may have waned while it remained under Jordan. </p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/193739/original/file-20171108-1987-199z3mk.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/193739/original/file-20171108-1987-199z3mk.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=130&fit=crop&dpr=1 600w, https://images.theconversation.com/files/193739/original/file-20171108-1987-199z3mk.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=130&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/193739/original/file-20171108-1987-199z3mk.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=130&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/193739/original/file-20171108-1987-199z3mk.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=163&fit=crop&dpr=1 754w, https://images.theconversation.com/files/193739/original/file-20171108-1987-199z3mk.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=163&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/193739/original/file-20171108-1987-199z3mk.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=163&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Figure 1. Strength of Earth’s magnetic field in 2010 (left) and 1000BC (right).</span>
<span class="attribution"><span class="source">Nature comms and https://academic.oup.com/gji/article/197/2/815/617637</span>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>All of these options suggest that behaviour of the liquid iron at the top of Earth’s core around 1000BC was very different to that seen today. Most of our knowledge of the core derives from roughly the last 200 years, corresponding to the time when direct magnetic field measurements have been available. Prior to discovery of the spike there was no reason to suspect that core flow speeds would be much different in 1000BC to today – indeed, the available models suggest there was little difference.</p>
<p>However, explaining the rapid changes associated with the spike requires flows <a href="https://www.sciencedirect.com/science/article/pii/S0012821X13006547">five to ten times those at present</a>, a large change in a short space of time. Moreover, such a narrow spike requires a similarly localised flow, which contrasts with the global-scale circulations we see today. The prospect that the iron core could flow faster and change more suddenly than previously thought, together with the possibility that even more extreme spike-like events occurred in the past, is challenging some conventional views on the dynamics of Earth’s core. </p>
<h2>Future impact?</h2>
<p>Changes in Earth’s magnetic field are not generally thought to have direct consequences for life, but there are potentially significant societal implications that arise from our reliance on electronic infrastructure. A variety of effects <a href="https://theconversation.com/why-the-earths-magnetic-poles-could-be-about-to-swap-places-and-how-it-would-affect-us-71910">can arise</a> from interactions between Earth’s magnetic field and charged particles reaching Earth from the sun. </p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/193744/original/file-20171108-27001-1w9t6s5.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/193744/original/file-20171108-27001-1w9t6s5.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/193744/original/file-20171108-27001-1w9t6s5.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/193744/original/file-20171108-27001-1w9t6s5.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/193744/original/file-20171108-27001-1w9t6s5.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=502&fit=crop&dpr=1 754w, https://images.theconversation.com/files/193744/original/file-20171108-27001-1w9t6s5.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=502&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/193744/original/file-20171108-27001-1w9t6s5.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=502&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Aurora during a geomagnetic storm.</span>
<span class="attribution"><span class="source">NASA</span></span>
</figcaption>
</figure>
<p>Of particular importance are geomagnetic storms (caused by the solar wind), which are known to cause power outages and disruption to satellite and communications systems. The economic implications of severe storms are estimated to <a href="https://news.agu.org/press-release/extreme-space-weather-induced-electricity-blackouts-could-cost-u-s-more-than-40-billion-daily/?utm_source=CPRE&utm_medium=email&utm_campaign=press%20releases&utm_content=17-03%20space%20weather%20economic%20impacts">run into billions of pounds</a> and their importance is now reflected in the <a href="https://www.gov.uk/government/publications/national-risk-register-of-civil-emergencies-2017-edition">national risk register</a>. </p>
<p>Geomagnetic storms tend to be most prevalent in regions where Earth’s magnetic field is unusually weak. Spikes are regions of unusually strong magnetic field, but a <a href="https://simple.wikipedia.org/wiki/Maxwell%27s_equations">fundamental law of nature</a> means that they must be accompanied by regions of weaker field elsewhere on the globe. The key question is whether the field gets a little bit weaker over a large region or becomes very weak in just a small region. The latter “anti-spike” scenario could be similar to or more extreme than the current south Atlantic weak spot. </p>
<p>Whether there will be more spikes is hard to say. Until very recently, the Jordanian spike was the only such event ever observed. However, there is now <a href="https://www.sciencedirect.com/science/article/pii/S0012821X16300760">tantalising new evidence</a> for another spike-like feature in Texas, also around 1000BC. Our understanding of what spikes should look like, how they change in time, and <a href="https://www.nature.com/articles/ncomms15593">how they relate to the motion</a> of the liquid iron in Earth’s core are also improving rapidly. </p>
<p>Coupled with numerical simulations that model the dynamics of Earth’s core, it may soon be possible to make the first predictions of how often spikes occur and the most likely locations where they could have occurred in the past (and may occur in the future). It could turn out that they are more common than we think.</p><img src="https://counter.theconversation.com/content/86638/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Christopher Davies receives funding from NERC (project reference NE/L011328/1). </span></em></p>A strange patch of extremely strong magnetic field occurred over Jordan in 1000BC. Could we be about to face another one?Christopher Davies, NERC Independent Research Fellow/Lecturer in Geophysics, University of LeedsLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/850122017-10-16T13:11:53Z2017-10-16T13:11:53ZHow we used the Earth’s magnetic field to date rocks rich in dinosaur fossils<figure><img src="https://images.theconversation.com/files/189742/original/file-20171011-16636-s6gmqy.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Barkly Pass, the stratotype for the Elliot Formation. These beautiful rocks hold ancient secrets.</span> <span class="attribution"><span class="source">Lara Sciscio</span></span></figcaption></figure><p>Covering two thirds of South Africa the <a href="http://www.sciencedirect.com/science/article/pii/S1464343X05001184">Karoo Basin</a>, visually, is a beautiful space. When looking more deeply into its rock layers, like leafing through the pages of a book, one can read about a wealth of palaeoevinromental and biological processes. </p>
<p>The Karoo Basin is an invaluable archive of information over its 120 million year depositional history. Rich in fossils, both plants and animals, the Karoo Basin records crisis periods – mass extinction events – in the distant past when many species became extinct.</p>
<p>So far, there have been five main mass extinction events globally. The biggest, the <a href="http://science.nationalgeographic.com/science/prehistoric-world/permian-extinction/">end-Permian</a>, about 252 million years ago, was the Earth’s largest ecological disaster. The Karoo Basin also holds evidence of the third largest mass extinction. This occurred at the end of the Triassic, about 200 million years ago, and heralded the rise of the dinosaurs.</p>
<p>Understanding these climate change events and their impact on biology in the Karoo Basin could influence the way we look at the sixth extinction, which is happening now: the <a href="https://www.smithsonianmag.com/science-nature/what-is-the-anthropocene-and-are-we-in-it-164801414/">Anthropocene</a>. </p>
<p>Scientists need to know when the ancient extinctions happened and for how long. These events are recorded in layers of rock. So we need to know the age of those rocks. There are certain “geological clocks” which help when dating rocks: a mineral called zircon is one. Fossil pollen and spores are others. But when these are scarce, we need another way of measuring the age of rocks. And the Earth’s own magnetic field provides a useful source.</p>
<h2>A different technique</h2>
<p>My colleagues and I were interested in the age of a specific rock unit in the Karoo Basin: the <a href="http://sajg.geoscienceworld.org/content/118/3/311">Elliot Formation</a>. Rocks of the Elliot Formation outcrop in a ring around the Drakensberg Plateau (see figure). The Elliot Formation contains many fossils that shed light on the existence and evolution of dinosaurs in southern Africa. </p>
<figure class="align-left zoomable">
<a href="https://images.theconversation.com/files/190136/original/file-20171013-11722-9mss76.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/190136/original/file-20171013-11722-9mss76.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/190136/original/file-20171013-11722-9mss76.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=1113&fit=crop&dpr=1 600w, https://images.theconversation.com/files/190136/original/file-20171013-11722-9mss76.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=1113&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/190136/original/file-20171013-11722-9mss76.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=1113&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/190136/original/file-20171013-11722-9mss76.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=1399&fit=crop&dpr=1 754w, https://images.theconversation.com/files/190136/original/file-20171013-11722-9mss76.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=1399&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/190136/original/file-20171013-11722-9mss76.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=1399&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption"></span>
<span class="attribution"><span class="source">Lara Sciscio</span></span>
</figcaption>
</figure>
<p>This is especially interesting as the Formation is thought to span the end-Triassic mass extinction event. However, the age of the Elliot Formation and where this extinction event occurred within its rock layers was debated. </p>
<p>As there are no radiometric dates from zircons for the Elliot Formation, we used the Earth’s ancient geomagnetic field as a dating tool. This technique has been used globally on <a href="https://www.news.uct.ac.za/article/-2017-09-01-geological-barcodes-a-unique-way-to-date-rocks">similar aged rocks</a>. Applying it here enabled us to narrow down the age of the Elliot Formation to somewhere between about 213 million and 195 million years old. </p>
<p>These dates may help us to answer broader questions relating to the severity of the end-Triassic mass extinction and the post-extinction recovery period in southern Africa. This time line is particularly useful in measuring the diversity of dinosaurs across the bio-crisis and during a critical time in their evolution.</p>
<h2>Magnetic flips</h2>
<p>The Earth generates and sustains a <a href="http://www.physics.org/article-questions.asp?id=64">magnetic field</a> through the motion of the liquid outer core. Some minerals in rocks are able to record the Earth’s magnetic field when they are deposited. Two such minerals, hematite and maghemite, are prevalent in the Elliot Formation. In fact, they lend the Formation a distinct brick-red colour. </p>
<p>Our research <a href="http://www.sciencedirect.com/science/article/pii/S1342937X16302593?via%3Dihub">has found</a> that minerals within the rocks of the Elliot Formation are able to retain primary magnetisations: they have reliably recorded the Earth’s magnetic field at the time of their deposition. That’s important because natural processes can cause “overprinting” – wiping out the original magnetic signature.</p>
<p>This method has been used within the Karoo Basin before on older rocks, but it’s never guaranteed that rocks will retain their primary magnetic signatures. The fact that the Elliot Formation, largely, didn’t fall prey to “overprinting” is what allowed us to record the pattern of the ancient magnetic field.</p>
<h2>Pole reversal offers timing tool</h2>
<p>The Earth’s magnetic field is not constant through time. It “flips” or “reverses” at irregular intervals; on average, every few million years.</p>
<p>When this happens, the magnetic north pole is direct to the geographic south pole and vice versa. Rocks contain alternating layers of north- and south-directed minerals corresponding to every “flip” event. This creates distinct geomagnetic polarity chron(s) – a name to define a specific unit of time during reversals – for any given time period. </p>
<p>By studying the rates and number of these reversals recorded in the Elliot Formation’s rocks, we are able to get a more accurate idea of the rocks’ age. </p>
<p>The next step in pinpointing the Elliot Formation’s relative age was to build its unique magnetic polarity time scale – a log of all the reversal events.</p>
<p>This involved drilling out small samples of rock, using a portable hand-held drill, and orientating them, using a special compass in the field. Thereafter samples were processed in the <a href="https://www.uj.ac.za/faculties/science/geology/Pages/Paleomag-lab.aspx">Paleomag Lab</a> at the University of Johannesburg to recover their unique geomagnetic polarity history. </p>
<p>By doing this, we could build a composite magnetic polarity chronology for the Elliot Formation. We were then able to compare these rocks from South Africa and neighbouring Lesotho to others of a similar time period globally. In so doing, the Elliot Formation records the Earth’s magnetic field as it was about 200 million years ago.</p>
<p>We are not the only ones trying to pin down this important rock unit’s age. We hope that our work will provide a framework on which to place other kinds of information produced by others in this and related fields.</p><img src="https://counter.theconversation.com/content/85012/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Lara Sciscio receives funding from DST-NRF Centre of Excellence in Palaeosciences (CoE in Palaeosciences). </span></em></p>The earth’s own magnetic field offers a useful way to measure the age of rocks - information that can help unpack ancient events and aid our understanding of the present.Lara Sciscio, Postdoctoral Research Fellow in Geological Sciences, University of Cape TownLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/841542017-09-18T12:39:13Z2017-09-18T12:39:13ZWhat we’re hoping to learn from the magnetic readings of Cassini’s final orbits<figure><img src="https://images.theconversation.com/files/186211/original/file-20170915-29578-oxudom.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Mission control loses signal from Cassini.</span> <span class="attribution"><span class="source">NASA/Joel Kowsky</span>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span></figcaption></figure><p>It was a proud but sad moment when NASA announced that mission control <a href="https://theconversation.com/cassini-crashes-its-time-for-a-new-mission-to-explore-the-possibility-of-life-on-saturns-moons-84016">had lost the signal</a> from the Cassini spacecraft on September 15. As it takes the signal over an hour to travel from Saturn to Earth, this meant that the spacecraft had already been destroyed in Saturn’s atmosphere.</p>
<p>I was at Caltech in the US, watching the final moments of action on big screens together with mostof the other scientists, engineers and project managers who have worked very hard to make Cassini a success. The spacecraft, now a memory, leaves us with an <a href="https://theconversation.com/bittersweet-feeling-as-cassini-mission-embarks-on-its-grand-finale-ahead-of-death-plunge-76670">enormous legacy</a> – a dataset that will take decades to fully exploit. In fact, I’m sure it’ll launch many more scientific careers in the process.</p>
<p>I am co-investigator on Cassini’s <a href="https://saturn.jpl.nasa.gov/magnetometer/">magnetometer instrument</a>. Using measurements of magnetic fields around Saturn, we have probed the planet’s interior as well as the environments of its moons Titan and Enceladus.</p>
<p>The magnetometer is an instrument with sensors perched on an 11-metre boom, which extends out from the side of the spacecraft. This arrangement is necessary to minimise the interference of magnetic fields caused by the spacecraft electronics. </p>
<p>Scientists on our team have been mapping the magnetic field generated inside Saturn since 2004. We have also mapped the <a href="http://www.esa.int/Our_Activities/Space_Science/Cassini-Huygens/Saturn_s_magnetosphere">planet’s “magnetosphere” </a> – an enormous region or “bubble” of space around the planet which is influenced by its magnetic field. The region, filled with charged particles called plasma, produces a cavity in the flow of particles from the sun (the solar wind). </p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/186210/original/file-20170915-4751-1w0xw1z.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/186210/original/file-20170915-4751-1w0xw1z.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/186210/original/file-20170915-4751-1w0xw1z.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/186210/original/file-20170915-4751-1w0xw1z.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/186210/original/file-20170915-4751-1w0xw1z.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/186210/original/file-20170915-4751-1w0xw1z.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/186210/original/file-20170915-4751-1w0xw1z.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=566&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Dynamic atmosphere on Saturn’s icy moon Enceladus.</span>
<span class="attribution"><span class="source">NASA</span></span>
</figcaption>
</figure>
<p>Our instrument was the first to report something unusual at the first flybys of Enceladus. The field measurements indicated that Enceladus seemed to have something like a very extended “atmosphere” of sorts. These data were sufficient to convince mission control to fly even closer to Enceladus on the next flybys – enabling the spacecraft to obtain images of <a href="https://theconversation.com/icy-plumes-bursting-from-saturns-moon-enceladus-suggest-it-could-harbour-life-38673">incredible water plumes</a>, or geysers, from cracks in the icy surface of the moon. We now know that this source of water is also the principal source of plasma in the planet’s magnetosphere – making the small moon a tiny but powerful engine that drives the much more enormous magnetosphere of its parent planet.</p>
<h2>Deep mysteries</h2>
<p>Saturn’s internal field is almost perfectly symmetric about the planet’s axis of rotation – making it almost unique among the planets that have magnetic fields, such as Earth. Magnetic fields are produced by electric currents. On Earth, the magnetic field is produced by a fluid movement of molten iron around the planet’s core. It is unclear exactly how Saturn’s magnetic field is produced. We think its interior contains a layer made up of hydrogen that’s been crushed into a metallic liquid. Currents in this liquid are probably the cause of the strong magnetic field. </p>
<p>Cassini’s last few orbits, which brought it closer to the planet than it has ever been, will be critical to solve this and other questions. The data may help us confirm whether there are any other features of its interior that could be generating its magnetic field.</p>
<p>We are also hoping to accurately measure a tiny part of the field that we know isn’t symmetrical. This could help us to unambiguously pin down the rotation period of Saturn itself – that is, the exact length of a day (we currently think it is about 10 hours and 47 minutes). That’s because gas giants do not have a solid surface to track, which can make it hard to measure their exact rotation periods. Scientists have previously measured the repetition of radio signals as a proxy, but values based on such measurements vary. Measurements of changes in the magnetic field as the planet rotates, however, <a href="https://saturn.jpl.nasa.gov/news/2358/cassini-offers-new-hints-on-length-of-saturns-day/">may be more reliable</a>.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/186373/original/file-20170918-8264-haxrob.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/186373/original/file-20170918-8264-haxrob.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/186373/original/file-20170918-8264-haxrob.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/186373/original/file-20170918-8264-haxrob.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/186373/original/file-20170918-8264-haxrob.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/186373/original/file-20170918-8264-haxrob.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/186373/original/file-20170918-8264-haxrob.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=566&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">False-color image showing aurora at south pole.</span>
<span class="attribution"><span class="source">NASA/JPL/University of Arizona/University of Leicester</span></span>
</figcaption>
</figure>
<p>Cassini confirmed the earlier discovery by the Voyager spacecraft that there’s a <a href="https://www.imperial.ac.uk/college.asp?P=7741">periodic “signal” in the magnetic field</a> throughout the planet’s magnetosphere. We have good reason to believe that this signal is an indication of energy being transferred from flows in the planet’s atmosphere out to its magnetosphere. This energy is transported over distances of millions of kilometres, and the magnetic field acts as the “wire” along which this energy is transported. Understanding the process is important – we know that this “coupling” between the planet’s atmosphere and magnetosphere also plays a central role in the <a href="https://www.nasa.gov/multimedia/imagegallery/image_feature_1083.html">physics of auroras (northern lights) and plasmas</a> at Saturn and other magnetised planets.</p>
<p>Our team is just one of many working on data collected by Cassini, meaning it’s likely we will learn a lot more about the planet as we go forward. For now, the end of mission should be viewed as a commemoration of an enormously successful international, scientific project – and a timely reminder of what humans can achieve when we respect each others’ abilities and differences, so that we can work together towards a common goal. So, goodbye Cassini, you will be missed but never forgotten.</p><img src="https://counter.theconversation.com/content/84154/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Nick Achilleos receives funding from STFC, and is also a participant in Europlanet H2020.</span></em></p>Cassini may be gone but the data it left behind could help reveal how long Saturn’s day is and how its magnetic field is generated.Nick Achilleos, Professor of Planetary Physics, UCLLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/775352017-05-15T12:00:34Z2017-05-15T12:00:34ZA giant lava lamp inside the Earth might be flipping the planet’s magnetic field<figure><img src="https://images.theconversation.com/files/169328/original/file-20170515-6984-1u4gelz.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><span class="source">Shutterstock</span></span></figcaption></figure><p>If you could travel back in time 41,000 years to the last ice age, your compass would point south instead of north. That’s because for a period of a few hundred years, the <a href="https://phys.org/news/2012-10-extremely-reversal-geomagnetic-field-climate.html">Earth’s magnetic field was reversed</a>. Magnetic <a href="https://theconversation.com/why-the-earths-magnetic-poles-could-be-about-to-swap-places-and-how-it-would-affect-us-71910">reversals have happened repeatedly</a> over the planet’s history, sometimes lasting hundreds of thousands of years. We know this from the way it affects the alignment of magnetic minerals, that we can now study on the Earth’s surface.</p>
<p>Several ideas exist to explain why magnetic field reversals happen. <a href="http://www.sciencedirect.com/science/article/pii/S0012821X15000345">One of these</a> just became more plausible. My colleagues and I discovered that regions on top of the Earth’s core could behave like giant lava lamps, with blobs of rock periodically rising and falling deep inside our planet. This could affect its magnetic field and cause it to flip. The way we made this discovery was by studying signals from some of the world’s most destructive earthquakes.</p>
<p>Around 3,000km below our feet – 270 times further down than the deepest part of the ocean – is the start of the Earth’s core, a liquid sphere of mostly molten iron and nickel. At this <a href="https://www.scientificamerican.com/article/the-core-mantle-boundary-2005-07/">boundary between the core</a> and the rocky mantle above, the temperature is almost 4,000°C degrees, similar to that on the surface of a star, with a pressure more than 1.3m times that at the Earth’s surface.</p>
<p>On the mantle side of this boundary, solid rock gradually flows over millions of years, driving the plate tectonics that cause continents to move and change shape. On the core side, fluid, magnetic iron swirls vigorously, creating and sustaining the Earth’s magnetic field that protects the planet from the radiation of space that would otherwise strip away our atmosphere.</p>
<p>Because it is so far underground, the main way we can study the core-mantle boundary is by looking at the seismic signals generated by earthquakes. Using information about the shape and speed of seismic waves, we can work out what the part of the planet they have travelled through to reach us is like. After a particularly large earthquake, the whole planet vibrates like a ringing bell, and measuring these oscillations in different places can tell us how the structure varies within the planet.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/169329/original/file-20170515-7009-kt9j8t.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/169329/original/file-20170515-7009-kt9j8t.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/169329/original/file-20170515-7009-kt9j8t.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/169329/original/file-20170515-7009-kt9j8t.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/169329/original/file-20170515-7009-kt9j8t.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/169329/original/file-20170515-7009-kt9j8t.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/169329/original/file-20170515-7009-kt9j8t.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">New model Earth?</span>
<span class="attribution"><span class="source">Shutterstock</span></span>
</figcaption>
</figure>
<p>In this way, we know there are two large regions at the top of the core where seismic waves travel more slowly than in surrounding areas. Each region is so large that it would be 100 times taller than Mount Everest if it were on the surface of the planet. These regions, termed <a href="http://www.nature.com/ngeo/journal/v9/n7/abs/ngeo2733.html">large-low-velocity-provinces</a> or more often just “blobs”, have a significant impact on the dynamics of the mantle. They also influence how the core cools, which alters the flow in the outer core. </p>
<p>Several particularly destructive earthquakes over recent decades have enabled us to measure a special kind of seismic oscillations that travel along the core-mantle boundary, <a href="http://onlinelibrary.wiley.com/doi/10.1002/grl.50514/full">known as Stoneley modes</a>. <a href="https://www.nature.com/articles/ncomms15241">Our most recent research</a> on these modes shows that the two blobs on top of the core have a lower density compared to the surrounding material. This suggests that material is actively rising up towards the surface, consistent with other geophysical observations. </p>
<h2>New explanation</h2>
<p>These regions might be less dense simply because they are hotter. But an exciting alternative possibility is that the chemical composition of these parts of the mantle cause them to behave like the blobs in a lava lamp. This would mean they heat up and periodically rise towards the surface, before cooling and splashing back down on the core.</p>
<p>Such behaviour would change the way in which heat is extracted from the core’s surface over millions of years. And this <a href="http://www.sciencedirect.com/science/article/pii/S0012821X15000345">could explain</a> why the Earth’s magnetic field sometimes reverses. The fact that the field has changed so many times in the Earth’s history suggests that the internal structure we know today may also have changed.</p>
<p>We know the core is covered with a landscape of mountains and valleys like the Earth’s surface. By using more data from Earth oscillations to study this topography, we will be able to produce more detailed maps of the core that will give us a much better understanding of what is going on deep below our feet.</p><img src="https://counter.theconversation.com/content/77535/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Paula Koelemeijer receives funding from University College, Oxford. </span></em></p>Signals from violent earthquakes are helping reveal the landscape of the planet’s insides.Paula Koelemeijer, Postdoctoral Fellow in Global Seismology, University of OxfordLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/475282017-02-06T04:52:22Z2017-02-06T04:52:22ZDoes an anomaly in the Earth’s magnetic field portend a coming pole reversal?<figure><img src="https://images.theconversation.com/files/155051/original/image-20170131-3248-1n8ah.jpg?ixlib=rb-1.1.0&rect=382%2C12%2C3873%2C2707&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">What's north would become south.</span> <span class="attribution"><a class="source" href="https://spaceflight.nasa.gov/gallery/images/station/crew-23/html/iss023e058455.html">NASA </a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span></figcaption></figure><p>The Earth is blanketed by a magnetic field. It’s what makes compasses point north, and protects our atmosphere from continual bombardment from space by charged particles such as protons. Without a magnetic field, our atmosphere would slowly be stripped away by harmful radiation, and life would almost certainly not exist as it does today.</p>
<p>You might imagine the magnetic field is a timeless, constant aspect of life on Earth, and to some extent you would be right. But Earth’s magnetic field actually does change. Every so often – on the order of several hundred thousand years or so – the magnetic field has flipped. North has pointed south, and vice versa. And when the field flips it also tends to become very weak.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/154585/original/image-20170127-30413-incc40.gif?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/154585/original/image-20170127-30413-incc40.gif?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=328&fit=crop&dpr=1 600w, https://images.theconversation.com/files/154585/original/image-20170127-30413-incc40.gif?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=328&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/154585/original/image-20170127-30413-incc40.gif?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=328&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/154585/original/image-20170127-30413-incc40.gif?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=412&fit=crop&dpr=1 754w, https://images.theconversation.com/files/154585/original/image-20170127-30413-incc40.gif?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=412&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/154585/original/image-20170127-30413-incc40.gif?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=412&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">On the left, the Earth’s magnetic field we’re used to. On the right, a model of what the magnetic field might be like during a reversal.</span>
<span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:NASA_54559main_comparison1_strip.gif">NASA/Gary Glazmaier</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<p>What currently has geophysicists like us abuzz is the realization that the strength of Earth’s magnetic field has been decreasing for the last 160 years at an alarming rate. This collapse is centered in a huge expanse of the Southern Hemisphere, extending from Zimbabwe to Chile, known as the South Atlantic Anomaly. The magnetic field strength is so weak there that it’s a hazard for satellites that orbit above the region – the field no longer protects them from <a href="http://scitechdaily.com/new-hubblecast-video-explores-south-atlantic-anomaly/">radiation which interferes</a> with satellite electronics.</p>
<p>And the field is continuing to grow weaker, potentially portending even more dramatic events, including a global reversal of the magnetic poles. Such a major change would affect our navigation systems, as well as the transmission of electricity. The spectacle of the northern lights might appear at different latitudes. And because more radiation would reach Earth’s surface under very low field strengths during a global reversal, it also might affect rates of cancer.</p>
<p>We still don’t fully understand what the extent of these effects would be, adding urgency to our investigation. We’re turning to some perhaps unexpected data sources, including 700-year-old African archaeological records, to puzzle it out.</p>
<h2>Genesis of the geomagnetic field</h2>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/154587/original/image-20170127-30424-1tgdu3e.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/154587/original/image-20170127-30424-1tgdu3e.png?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/154587/original/image-20170127-30424-1tgdu3e.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=371&fit=crop&dpr=1 600w, https://images.theconversation.com/files/154587/original/image-20170127-30424-1tgdu3e.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=371&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/154587/original/image-20170127-30424-1tgdu3e.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=371&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/154587/original/image-20170127-30424-1tgdu3e.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=466&fit=crop&dpr=1 754w, https://images.theconversation.com/files/154587/original/image-20170127-30424-1tgdu3e.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=466&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/154587/original/image-20170127-30424-1tgdu3e.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=466&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Cutaway image of the Earth’s interior.</span>
<span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:Earth_poster.svg">Kelvinsong</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<p>Earth’s magnetic field is created by <a href="http://www.geomag.bgs.ac.uk/education/earthmag.html#_Toc2075563">convecting iron in our planet’s liquid outer core</a>. From the wealth of <a href="https://www.ngdc.noaa.gov/geomag/geomag.shtml">observatory and satellite data</a> that document the magnetic field of recent times, we can model what the field would look like if we had a compass immediately above the Earth’s swirling liquid iron core. </p>
<p>These analyses reveal an astounding feature: There’s a patch of reversed polarity beneath southern Africa at the core-mantle boundary where the liquid iron outer core meets the slightly stiffer part of the Earth’s interior. In this area, the polarity of the field is opposite to the average global magnetic field. If we were able to use a compass deep under southern Africa, we would see that in this unusual patch north actually points south.</p>
<p>This patch is the main culprit creating the South Atlantic Anomaly. In numerical simulations, unusual patches similar to the one beneath southern Africa appear immediately prior to geomagnetic reversals.</p>
<p>The poles have reversed frequently over the history of the planet, but the <a href="http://doi.org/10.1002/ggge.20263">last reversal is in the distant past</a>, some 780,000 years ago. The rapid decay of the recent magnetic field, and its pattern of decay, naturally raises the question of what was happening prior to the last 160 years.</p>
<h2>Archaeomagnetism takes us further back in time</h2>
<p>In archaeomagnetic studies, geophysicists team with archaeologists to learn about the past magnetic field. For example, clay used to make pottery contains small amounts of magnetic minerals, such as magnetite. When the clay is heated to make a pot, its magnetic minerals lose any magnetism they may have held. Upon cooling, the magnetic minerals record the direction and intensity of the magnetic field at that time. If one can determine the age of the pot, or the archaeological site from which it came (using radiocarbon dating, for instance), then an archaeomagnetic history can be recovered. </p>
<p>Using this kind of data, we have a partial history of archaeomagnetism for the Northern Hemisphere. In contrast, the Southern Hemisphere archaeomagnetic record is scant. In particular, there have been virtually no data from southern Africa – and that’s the region, <a href="http://dx.doi.org/10.1016/j.epsl.2011.03.030">along with South America</a>, that might provide the most insight into the history of the reversed core patch creating today’s South Atlantic Anomaly.</p>
<p>But the ancestors of today’s southern Africans, Bantu-speaking metallurgists and farmers who began to migrate into the region between 2,000 and 1,500 years ago, unintentionally left us some clues. <a href="http://doi.org/10.1146/annurev.an.11.100182.001025">These Iron Age people</a> lived in huts built of clay, and stored their grain in hardened clay bins. As the <a href="http://www.sahistory.org.za/article/pre-1500">first agriculturists of the Iron Age of southern Africa</a>, they relied heavily on rainfall. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/154840/original/image-20170130-7693-ejv2dc.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/154840/original/image-20170130-7693-ejv2dc.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/154840/original/image-20170130-7693-ejv2dc.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/154840/original/image-20170130-7693-ejv2dc.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/154840/original/image-20170130-7693-ejv2dc.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/154840/original/image-20170130-7693-ejv2dc.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/154840/original/image-20170130-7693-ejv2dc.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/154840/original/image-20170130-7693-ejv2dc.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=566&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Grain bins of the style used centuries ago.</span>
<span class="attribution"><span class="source">John Tarduno</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<p>The communities often responded to times of drought with rituals of cleansing that involved burning mud granaries. This somewhat tragic series of events for these people was ultimately a boon many hundreds of years later for archaeomagnetism. Just as in the case of the firing and cooling of a pot, the clay in these structures recorded Earth’s magnetic field as they cooled. Because the floors of these ancient huts and grain bins can sometimes be found intact, we can sample them to obtain a record of both the direction and strength of their contemporary magnetic field. Each floor is a small magnetic observatory, with its compass frozen in time immediately after burning.</p>
<p><a href="http://dx.doi.org/10.1038/ncomms8865">With our colleagues, we’ve focused our sampling</a> on Iron Age village sites that dot the Limpopo River Valley, bordered today by Zimbabwe to the north, Botswana to the west and South Africa to the south.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/154841/original/image-20170130-7693-1w1eu3f.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/154841/original/image-20170130-7693-1w1eu3f.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/154841/original/image-20170130-7693-1w1eu3f.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=196&fit=crop&dpr=1 600w, https://images.theconversation.com/files/154841/original/image-20170130-7693-1w1eu3f.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=196&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/154841/original/image-20170130-7693-1w1eu3f.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=196&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/154841/original/image-20170130-7693-1w1eu3f.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=246&fit=crop&dpr=1 754w, https://images.theconversation.com/files/154841/original/image-20170130-7693-1w1eu3f.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=246&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/154841/original/image-20170130-7693-1w1eu3f.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=246&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">What’s happening deep within the Earth, beneath the Limpopo River Valley?</span>
<span class="attribution"><span class="source">John Tarduno</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<h2>Magnetic field in flux</h2>
<p>Sampling at Limpopo River Valley locations has yielded the first archaeomagnetic history for southern Africa between A.D. 1000 and 1600. What we found reveals a period in the past, near A.D. 1300, when the field in that area was decreasing as rapidly as it is today. Then the intensity increased, albeit at a much slower rate.</p>
<p>The occurrence of two intervals of rapid field decay – one 700 years ago and one today – suggests a recurrent phenomenon. Could the reversed flux patch presently under South Africa have happened regularly, further back in time than our records have shown? If so, why would it occur again in this location?</p>
<p>Over the last decade, researchers have accumulated <a href="http://dx.doi.org/10.1016/j.epsl.2005.01.037">images from the analyses of earthquakes’ seismic waves</a>. As seismic shear waves move through the Earth’s layers, the speed with which they travel is an indication of the density of the layer. Now we know that a large area of slow seismic shear waves characterizes the core mantle boundary beneath southern Africa.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/157392/original/image-20170218-10195-1qexrl5.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/157392/original/image-20170218-10195-1qexrl5.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/157392/original/image-20170218-10195-1qexrl5.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=364&fit=crop&dpr=1 600w, https://images.theconversation.com/files/157392/original/image-20170218-10195-1qexrl5.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=364&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/157392/original/image-20170218-10195-1qexrl5.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=364&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/157392/original/image-20170218-10195-1qexrl5.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=457&fit=crop&dpr=1 754w, https://images.theconversation.com/files/157392/original/image-20170218-10195-1qexrl5.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=457&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/157392/original/image-20170218-10195-1qexrl5.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=457&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Location of the South Atlantic Anomaly.</span>
<span class="attribution"><span class="source">Michael Osadicw/John Tarduno</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<p>This particular region underneath southern Africa has the somewhat wordy title of the African Large Low Shear Velocity Province. While many wince at the descriptive but jargon-rich name, it is a profound feature that must be tens of millions of years old. While thousands of kilometers across, its boundaries are sharp. Interestingly, the reversed core flux patch is nearly coincident with its eastern edge.</p>
<p>The fact that the present-day reversed core patch and the edge of the African Large Low Shear Velocity Province are physically so close got us thinking. We’ve come up with a <a href="http://dx.doi.org/10.1038/ncomms8865">model linking the two phenomena</a>. We suggest that the unusual African mantle changes the flow of iron in the core underneath, which in turn changes the way the magnetic field behaves at the edge of the seismic province, and leads to the reversed flux patches. </p>
<p>We speculate that these reversed core patches grow rapidly and then wane more slowly. Occasionally one patch may grow large enough to dominate the magnetic field of the Southern Hemisphere – and the poles reverse.</p>
<p>The conventional idea of reversals is that they can start anywhere in the core. Our conceptual model suggests there may be special places at the core-mantle boundary that promote reversals. We do not yet know if the current field is going to reverse in the next few thousand years, or simply continue to <a href="https://doi.org/10.3389/feart.2015.00061">weaken over the next couple of centuries</a>.</p>
<p>But the clues provided by the ancestors of modern-day southern Africans will undoubtedly help us to further develop our proposed mechanism for reversals. If correct, pole reversals may be “Out of Africa.”</p>
<hr>
<p><em>This story was updated to correct the units used in the last figure; magnetic field strength is depicted in tens of nanoTesla.</em></p><img src="https://counter.theconversation.com/content/47528/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>John Tarduno receives funding from the US National Science Foundation. </span></em></p><p class="fine-print"><em><span>Vincent Hare receives funding from the US National Science Foundation and !Khure Africa, a dual South Africa/France collaborative Earth System programme. </span></em></p>Are we headed to a magnetic reversal and all the global disruption that would bring? Enter archaeomagnetism. A look at the archaeological record in southern Africa provides some clues.John Tarduno, Professor of Geophysics, University of RochesterVincent Hare, Postdoctoral Associate in Earth and Environmental Sciences, University of RochesterLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/719102017-01-27T09:02:04Z2017-01-27T09:02:04ZWhy the Earth’s magnetic poles could be about to swap places – and how it would affect us<figure><img src="https://images.theconversation.com/files/154278/original/image-20170125-23851-8inepe.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">The Earth's magnetic field is hugely important to our survival.</span> <span class="attribution"><span class="source">NASA Goddard Space Flight Centre/Flickr</span>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span></figcaption></figure><p>The Earth’s <a href="https://theconversation.com/earths-magnetic-heartbeat-a-thinner-past-and-new-alien-worlds-59442">magnetic field</a> surrounds our planet like an invisible force field – protecting life from harmful solar radiation by deflecting charged particles away. Far from being constant, this field is continuously changing. Indeed, our planet’s history includes at least several hundred global magnetic reversals, where north and south magnetic poles swap places. So when’s the next one happening and how will it affect life on Earth? </p>
<p>During a reversal the magnetic field won’t be zero, but will assume a weaker and more complex form. It <a href="http://scrippsscholars.ucsd.edu/cconstable/content/earths-magnetic-field-reversing">may fall to</a> 10% of the present-day strength and have magnetic poles at the equator or even the simultaneous existence of multiple “north” and “south” magnetic poles. </p>
<p>Geomagnetic reversals occur a few times every million years on average. However, the interval between reversals is very irregular and can range up to tens of millions of years. </p>
<p>There can also be temporary and incomplete reversals, known as events and excursions, in which the magnetic poles move away from the geographic poles – perhaps even crossing the equator – before returning back to their original locations. The last full reversal, the Brunhes-Matuyama, occurred around 780,000 years ago. A temporary reversal, <a href="http://www.nature.com/nature/journal/v253/n5494/abs/253705a0.html">the Laschamp event</a>, occurred around 41,000 years ago. It lasted less than 1,000 years with the actual change of polarity lasting around 250 years. </p>
<h2>Power cut or mass extinction?</h2>
<p>The alteration in the magnetic field during a reversal will weaken its shielding effect, allowing heightened levels of radiation on and above the Earth’s surface. Were this to happen today, the increase in charged particles reaching the Earth would result in increased risks for satellites, aviation, and ground-based electrical infrastructure. Geomagnetic storms, driven by the interaction of anomalously large eruptions of solar energy with our magnetic field, give us a foretaste of what we can expect with a weakened magnetic shield.</p>
<p>In 2003, <a href="https://www.nasa.gov/topics/solarsystem/features/halloween_storms.html">the so-called Halloween storm</a> caused local electricity-grid blackouts in Sweden, required the rerouting of flights to avoid communication blackout and radiation risk, and disrupted satellites and communication systems. But this storm was minor in comparison with other storms of the recent past, such as the <a href="http://www.history.com/news/a-perfect-solar-superstorm-the-1859-carrington-event">1859 Carrington event</a>, which caused aurorae as far south as the Caribbean. </p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/154398/original/image-20170126-30413-1k0cpxu.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/154398/original/image-20170126-30413-1k0cpxu.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=278&fit=crop&dpr=1 600w, https://images.theconversation.com/files/154398/original/image-20170126-30413-1k0cpxu.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=278&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/154398/original/image-20170126-30413-1k0cpxu.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=278&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/154398/original/image-20170126-30413-1k0cpxu.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=349&fit=crop&dpr=1 754w, https://images.theconversation.com/files/154398/original/image-20170126-30413-1k0cpxu.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=349&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/154398/original/image-20170126-30413-1k0cpxu.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=349&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Aurora borealis.</span>
<span class="attribution"><span class="source">Soerfm/wikipedia</span>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<p>The impact of a major storm on today’s electronic infrastructure is not fully known. Of course any time spent without electricity, heating, air conditioning, GPS or internet would have a major impact; widespread blackouts could result in economic disruption<a href="http://news.agu.org/press-release/extreme-space-weather-induced-electricity-blackouts-could-cost-u-s-more-than-40-billion-daily/?utm_source=CPRE&utm_medium=email&utm_campaign=press%20releases&utm_content=17-03%20space%20weather%20economic%20impacts"> measuring in tens of billions of dollars a day</a>. </p>
<p>In terms of life on Earth and the direct impact of a reversal on our species we cannot definitively predict what will happen as modern humans did not exist at the time of the last full reversal. Several studies have tried to <a href="http://adsabs.harvard.edu/abs/1985Natur.314..341R">link past reversals with mass extinctions</a> – suggesting some reversals and episodes of extended volcanism <a href="http://www.sciencedirect.com/science/article/pii/S0012821X07003640,%20http://www.nature.com/ngeo/journal/v5/n8/full/ngeo1521.html">could be driven by a common cause</a>. However, there is no evidence of any impending cataclysmic volcanism and so we would only likely have to contend with the electromagnetic impact if the field does reverse relatively soon. </p>
<p>We do know that many animal species have some form of <a href="https://theconversation.com/no-fishy-business-salmon-use-earths-magnetic-field-to-migrate-22835">magnetoreception that enables them to sense the Earth’s magnetic field</a>. They may use this to assist in long-distance navigation during migration. But it is unclear what impact a reversal might have on such species. What is clear is that early humans did manage to live through the Laschamp event and life itself has survived the hundreds of full reversals evidenced in the geologic record.</p>
<h2>Can we predict geomagnetic reversals?</h2>
<p>The simple fact that we are “overdue” for a full reversal and the fact that the Earth’s field is currently decreasing at a rate of 5% per century, <a href="http://www.nature.com/nature/journal/v452/n7184/full/452165a.html">has led to suggestions</a> that the field may reverse within the next 2,000 years. But pinning down an exact date – at least for now – will be difficult.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/154274/original/image-20170125-23872-mjgami.gif?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/154274/original/image-20170125-23872-mjgami.gif?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=328&fit=crop&dpr=1 600w, https://images.theconversation.com/files/154274/original/image-20170125-23872-mjgami.gif?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=328&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/154274/original/image-20170125-23872-mjgami.gif?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=328&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/154274/original/image-20170125-23872-mjgami.gif?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=412&fit=crop&dpr=1 754w, https://images.theconversation.com/files/154274/original/image-20170125-23872-mjgami.gif?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=412&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/154274/original/image-20170125-23872-mjgami.gif?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=412&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Magnetic reversal.</span>
<span class="attribution"><span class="source">NASA.</span></span>
</figcaption>
</figure>
<p>The Earth’s magnetic field is generated within the liquid core of our planet, by the slow churning of molten iron. Like the atmosphere and oceans, the way in which it moves is governed by the laws of physics. We should therefore be able to predict the “weather of the core” by tracking this movement, just like we can predict real weather by looking at the atmosphere and ocean. A reversal can then be likened to a particular type of storm in the core, where the dynamics – and magnetic field – go haywire (at least for a short while), before settling down again. </p>
<p>The difficulties of predicting the weather beyond a few days are widely known, despite us living within and directly observing the atmosphere. Yet predicting the Earth’s core is a far more difficult prospect, principally because it is buried beneath 3,000km of rock such that our observations are scant and indirect. However, we are not completely blind: we know the major composition of the material inside the core and that it is liquid. A global network of ground-based observatories and orbiting satellites also measure how the magnetic field is changing, which gives us insight into how the liquid core is moving.</p>
<p>The recent discovery of a <a href="http://www.nature.com/ngeo/journal/v10/n1/full/ngeo2859.html">jet-stream</a> within the core highlights our evolving ingenuity and increasing ability to measure and infer the dynamics of the core. Coupled with numerical simulations and laboratory experiments to study the fluid dynamics of the planet’s interior, our understanding is developing at a rapid rate. The prospect of being able to forecast the Earth’s core is perhaps not too far out of reach.</p><img src="https://counter.theconversation.com/content/71910/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Phil Livermore receives funding from the Natural Environment Research Council.</span></em></p><p class="fine-print"><em><span>Jon Mound receives funding from the Natural Environment Research Council. </span></em></p>A geomagnetic reversal may have a severe impact on humans.Phil Livermore, Associate Professor of geophysics, University of LeedsJon Mound, Associate Professor of Geophysics, University of LeedsLicensed as Creative Commons – attribution, no derivatives.