tag:theconversation.com,2011:/ca/topics/magnetic-reversal-35326/articlesMagnetic reversal – The Conversation2019-09-16T20:35:31Ztag: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>
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<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>
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<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>
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<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>
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<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>
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<span class="caption">The declination angle varies between -90° and +90°.</span>
<span class="attribution"><span class="source">Author provided</span></span>
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<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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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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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/1145532019-05-06T10:36:49Z2019-05-06T10:36:49Z60 days in Iceberg Alley, drilling for marine sediment to decipher Earth’s climate 3 million years ago<figure><img src="https://images.theconversation.com/files/272054/original/file-20190501-113852-15dg0x7.JPG?ixlib=rb-1.1.0&rect=614%2C0%2C4226%2C2948&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">The research vessel must dodge dangerous icebergs as it drills for sediment core samples.</span> <span class="attribution"><span class="source">Phil Christie/IODP</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span></figcaption></figure><p>Competition is stiff for one of the 30 scientist berths on the <a href="https://joidesresolution.org/">JOIDES Resolution</a> research vessel. I’m one of the lucky ones, granted the opportunity to work 12-hour days, seven days a week for 60 days as part of <a href="https://joidesresolution.org/expedition/382/">Expedition 382 “Iceberg Alley”</a> in the Scotia Sea, just north of the Antarctic Peninsula.</p>
<p><a href="https://scholar.google.com/citations?user=ruUF3z4AAAAJ&hl=en&oi=ao">I’m a geologist who specializes in paleoceanography</a>. My research focuses on how Earth’s oceans and climate operated in the past; I’m especially interested in how much and how fast the Antarctic ice sheets melted between 2.5 to 4 million years ago, the last time atmospheric carbon dioxide levels were about 400 parts per million, as they are today. This work depends on collecting sediment samples from the ocean floor that were deposited during that time. These sediment layers are like a library of the Antarctic’s past environment.</p>
<p>The JOIDES Resolution is the only ship in the world with the drilling tools to collect both soft sediment and hard rock from the ocean – material that we recover in long cylinders called cores. No wonder researchers from all over the world, at all career stages, are excited to have traveled from India, Japan, Korea, the Netherlands, Germany, Spain, Switzerland, Brazil, China, Germany, Australia, the United Kingdom and, of course, the United States to join the expedition.</p>
<h2>Fieldwork 1,000 miles (1600 km) from port</h2>
<p>Two months is actually a short amount of time in which to address scientific research questions, but there have been years of careful planning and detailed preparation in advance of this expedition. We scientists onboard make best use of our limited time by drilling at what we’ve already agreed should be the most informative locations.</p>
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<iframe width="440" height="260" src="https://www.youtube.com/embed/4wJOt4fEVnU?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">An animation explains the drilling process.</span></figcaption>
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<p>When the ship arrives at the designated GPS location, the captain, the lab officer and the drilling engineer all check the position coordinates several times. With the ship’s thrusters keeping it precisely in place, workers lower coring equipment, including drill pipe, through an opening in the center of the ship. When the drill pipe reaches the coring depth – in our case ranging from 2,600 feet (800 meters) to 12,500 ft (3,800 m) – we lower a coring tool on a wireline down through the pipe.</p>
<p>Most of our cores are taken with an advanced hydraulic piston corer. In a process similar to using an elaborate cookie cutter, it punches through the ocean floor and collects a thin cylinder of the rock and sediment: our core sample. The wireline brings the 31-ft-long (9.5 m) core back to the ship. In the ship’s lab, we split the core lengthwise into an archive half – to be photographed and described – and a working half. This is the one we sample onboard for density, chemistry and magnetic properties.</p>
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<a href="https://images.theconversation.com/files/272319/original/file-20190502-103057-irmf68.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/272319/original/file-20190502-103057-irmf68.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/272319/original/file-20190502-103057-irmf68.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/272319/original/file-20190502-103057-irmf68.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/272319/original/file-20190502-103057-irmf68.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/272319/original/file-20190502-103057-irmf68.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/272319/original/file-20190502-103057-irmf68.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/272319/original/file-20190502-103057-irmf68.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">Co-chief scientist Michael Weber and sedimentologists (core describers) Suzanne O'Connell and Thomas Ronge examine the archive half of a split core at the describing table.</span>
<span class="attribution"><span class="source">Stefanie Brachfeld/IODP</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
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<p>Today the Greenland and Antarctic <a href="https://nsidc.org/cryosphere/quickfacts/icesheets.html">ice sheets contain 99% of Earth’s fresh water</a>. If all the Antarctic ice were to melt, average sea level would rise 200 feet (60 m). This won’t happen in your lifetime. But knowing how fast an event like this can occur – based on how fast ice has melted in the past – is critical to preparing for the sea level rise already accompanying Earth’s currently warming temperatures. Helping to understand that past change is one of the goals of our work on this expedition.</p>
<p>Establishing when it was that melting glaciers originally deposited the sediments we’re collecting is crucial and difficult. Only by dating this process can we figure out how fast the ice sheets disintegrated. There are two complementary approaches that researchers have traditionally used.</p>
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<a href="https://images.theconversation.com/files/272581/original/file-20190503-103068-ch7ai.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/272581/original/file-20190503-103068-ch7ai.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/272581/original/file-20190503-103068-ch7ai.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=452&fit=crop&dpr=1 600w, https://images.theconversation.com/files/272581/original/file-20190503-103068-ch7ai.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=452&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/272581/original/file-20190503-103068-ch7ai.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=452&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/272581/original/file-20190503-103068-ch7ai.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=568&fit=crop&dpr=1 754w, https://images.theconversation.com/files/272581/original/file-20190503-103068-ch7ai.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=568&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/272581/original/file-20190503-103068-ch7ai.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=568&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 microscopic fossil of diatom <em>Actinocyclus actinochilus</em>.</span>
<span class="attribution"><span class="source">Jonathan Warnock/Indiana University of Pennsylvania</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
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<p><a href="https://doi.org/10.1016/j.gloplacha.2012.05.017">Paleontologists look at tiny microfossils</a> from organisms such as <a href="https://doi.org/10.1038/nature08057">diatoms</a>, <a href="https://www.radiolaria.org/">radiolaria</a> and <a href="https://www.marum.de/Karin-Zonneveld/dinocystkey.html">dinocysts</a> that are found in the sediment cores. Then they can match up the species they spot in the samples with the timeframes they were known to exist. For instance, a paleontologist might know from previous research that a particular species of diatom lived between 1.8 and 2.6 million years ago. </p>
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<a href="https://images.theconversation.com/files/272318/original/file-20190502-103057-knhn72.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/272318/original/file-20190502-103057-knhn72.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/272318/original/file-20190502-103057-knhn72.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/272318/original/file-20190502-103057-knhn72.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/272318/original/file-20190502-103057-knhn72.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/272318/original/file-20190502-103057-knhn72.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/272318/original/file-20190502-103057-knhn72.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/272318/original/file-20190502-103057-knhn72.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">Sediment samples, called cubes, taken for future paleomagnetic research and marked styrofoam plugs identify where samples were taken for ‘moisture and density’ (MAD) measurements.</span>
<span class="attribution"><span class="source">Stefanie Brachfeld/IODP</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
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<p>A second method of dating depends on paleomagnetists measuring the strength and direction of the sediments’ magnetism. Over Earth’s history, the magnetic field has reversed, with magnetic north flipping to point south, at irregular intervals. Scientists <a href="https://wikipedia.org/wiki/Paleomagnetism">know when the reversals occurred</a>. In the period from 1.8 to 2.6 million years ago, for example, the magnetic field flipped four times.</p>
<p><a href="https://doi.org/10.1029/2012PA002308">The paleomagnetists look for reversals</a> in the alignment of magnetic minerals in the sediment we collect, and if they find them, they <a href="https://www.researchgate.net/profile/Ted_Moore/publication/272713726_Time_is_of_the_Essence/links/569cd6ae08ae2f0bdb8beab4/Time-is-of-the-Essence.pdf">can better identify when</a>, within that 1.8 to 2.6-million-year time interval, the sediment was deposited. If reversals are not present, it might mean the sediment accumulated so fast that only one magnetic interval is represented, or that part of the sediment record is missing. To determine which possibility is more likely, they talk to the people describing the visual properties of the core to see if there are abrupt changes that might indicate a disruption in the sedimentary record.</p>
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<a href="https://images.theconversation.com/files/272594/original/file-20190504-103068-i1law1.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/272594/original/file-20190504-103068-i1law1.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/272594/original/file-20190504-103068-i1law1.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/272594/original/file-20190504-103068-i1law1.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/272594/original/file-20190504-103068-i1law1.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/272594/original/file-20190504-103068-i1law1.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/272594/original/file-20190504-103068-i1law1.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/272594/original/file-20190504-103068-i1law1.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"></a>
<figcaption>
<span class="caption">Suzanne O'Connell points out details of the core on the description table.</span>
<span class="attribution"><span class="source">Lee Stephens/IODP</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<p>This sort of observation and consultation proceeds continuously as the cores come up and scientists work their shifts. For me, the joy of this at-sea experience is collaborating with other scientists on the same problem at the same time. If each of us was working in isolation in our own lab, collecting this much data would take years.</p>
<h2>Shipboard life</h2>
<p>Working alongside the scientists are 30 technicians who know how to operate the lab equipment, curate the hundreds of cores and keep all the computers running, and two outreach educators. All of this work is made possible by 65 people including a drilling crew, who operate the heavy equipment that collects the cores; the marine crew, who drive and maintain the ship; and the stewards who prepare the food, do the laundry and clean the ship.</p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/272316/original/file-20190502-103082-1pijf22.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/272316/original/file-20190502-103082-1pijf22.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/272316/original/file-20190502-103082-1pijf22.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=600&fit=crop&dpr=1 600w, https://images.theconversation.com/files/272316/original/file-20190502-103082-1pijf22.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=600&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/272316/original/file-20190502-103082-1pijf22.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=600&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/272316/original/file-20190502-103082-1pijf22.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=754&fit=crop&dpr=1 754w, https://images.theconversation.com/files/272316/original/file-20190502-103082-1pijf22.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=754&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/272316/original/file-20190502-103082-1pijf22.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">Loading food onto the JOIDES Resolution in Punta Arenas, Chile, to keep everyone fed during the two month expedition.</span>
<span class="attribution"><span class="source">Suzanne O'Connell/IODP</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<p>To feed 120 people for two months, 17 pallets of food are onloaded at each port call; each grocery order includes 12,000 eggs, a ton (976 kilograms) of potatoes and 800 lbs (360 kg) of butter. There’s a full-time baker, and the cooks prepare four full meals a day and provide snacks for four coffee breaks. A small gym is available to help to offset the abundant food. On some expeditions, people run on the helipad on the ship’s stern.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/272322/original/file-20190502-103045-1bhy1nm.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/272322/original/file-20190502-103045-1bhy1nm.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/272322/original/file-20190502-103045-1bhy1nm.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/272322/original/file-20190502-103045-1bhy1nm.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/272322/original/file-20190502-103045-1bhy1nm.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/272322/original/file-20190502-103045-1bhy1nm.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/272322/original/file-20190502-103045-1bhy1nm.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/272322/original/file-20190502-103045-1bhy1nm.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"></a>
<figcaption>
<span class="caption">Humpback whales are visible right alongside the JOIDES Resolution.</span>
<span class="attribution"><span class="source">Bridget Lee/IODP</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<p>It’s too cold and the seas are too rough for that on this expedition. Instead, we have the thrilling opportunity to see icebergs, whales and penguins. Few places in the ocean offer such a view – but plenty of danger comes with it.</p>
<p>With drill pipe extending 10,500 ft (3,200 m) – about two miles – to the sea floor and as much as a further 2,000 feet (600 m) into the hole, we would not be able to move quickly out of the way of an approaching iceberg. It can take two hours to remove the pipe from the hole. Since the ship is attached to the drill pipe, if an iceberg were fast approaching, there might not be enough time to retrieve the drill pipe – we’d have to break the connection with explosives. Hence, there’s a strict protocol for dealing with icebergs and an experienced ice observer onboard who helps monitor the speed and direction of the nearby icebergs.</p>
<h2>A drilling program that’s grown over decades</h2>
<p>Shipboard life has changed since <a href="https://theconversation.com/scientists-have-been-drilling-into-the-ocean-floor-for-50-years-heres-what-theyve-found-so-far-100309">my first participation in the scientific ocean drilling program</a> almost 40 years ago. Back then, onboard the program’s first drill ship, the Glomar Challenger, the internet and email were not an option. To contact a person on land, an amateur radio operator on the ship would contact a shore-based shortwave radio operator who would then place a collect call to the person you wanted to speak with. If the call was accepted, you could converse, ending each part of your message with “Over” to let the recipient know it was their turn to speak. Since the entire ship could hear the conversation, as well as anyone in the world listening on the radio, it wasn’t conducive to personal communication.</p>
<p>There are many other changes onboard. Core sections are now scanned by multiple machines that improve the interpretation of the data, and new tools allow better core recovery.</p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/272328/original/file-20190502-103082-1y11wat.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/272328/original/file-20190502-103082-1y11wat.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/272328/original/file-20190502-103082-1y11wat.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=475&fit=crop&dpr=1 600w, https://images.theconversation.com/files/272328/original/file-20190502-103082-1y11wat.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=475&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/272328/original/file-20190502-103082-1y11wat.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=475&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/272328/original/file-20190502-103082-1y11wat.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=597&fit=crop&dpr=1 754w, https://images.theconversation.com/files/272328/original/file-20190502-103082-1y11wat.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=597&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/272328/original/file-20190502-103082-1y11wat.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=597&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Co-chief scientists Michael Weber and Maureen Raymo in the JOIDES Resolution engine room.</span>
<span class="attribution"><span class="source">Sarah Kachovich/IODP</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<p>The most remarkable change, however, is in the composition of the scientific party. Today, half the scientists who go out are women, including the co-chief scientists – the people ultimately responsible for planning the expedition and for it reaching its scientific goals. During the entire Glomar Challenger program, from 1968 to 1983, only three of the 192 co-chief scientists were women.</p>
<p>Soon the expedition will be over, but the research will have only begun. After we’ve returned to our normal lives on land, we’ll continue to collaborate. I’ll be analyzing the size and composition of different parts of the sediment that came from land. Which parts were brought by icebergs, where did they originate, and when were they most active? How much of the sediment was transported by deep ocean currents or even by wind? Colleagues will be addressing the same questions but in the younger sediment, or determining the environmental conditions in which the microfossil communities thrived.</p>
<p>In two years, we’ll reconvene and spend several days presenting the results of our individual research. Each is a part of the larger puzzle about past climates and the rates and causes of climate change before the process was accelerated by human activity.</p><img src="https://counter.theconversation.com/content/114553/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Suzanne O'Connell receives funding from the U.S. Science Support Program, IODP, for participation in this expedition. She and her students have received funding to conduct research on prior scientific ocean drilling sediment samples, primarily from the Keck Geology Consortium, which is funded by the members schools (including Wesleyan University) and the National Science Foundation. She serves on the U.S. Advisory Committee for Scientific Ocean Drilling (USAC).</span></em></p>A paleooceanographer describes her ninth sea expedition, this time retrieving cylindrical ‘cores’ of the sediment and rock that’s as much as two miles down at the ocean floor.Suzanne OConnell, Professor of Earth & Environmental Sciences, Wesleyan UniversityLicensed 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/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.