Traditionally astronomers look out in space while geologists look down at Earth. But at the Astrogeobiology Laboratory we do astronomy by looking down deep into Earth’s sedimentary record. We try to link the history of Earth and its life to the astronomical realm. Whereas other research groups study the sedimentary strata for animal or plant fossils, or paleomagnetic, sea-level or climatic signatures, we search for material of extraterrestrial origin.
In one of our projects we dissolve in strong acids tons of sedimentary rocks that formed on sea floors up to 3.5 billion years ago. From the rocks we extract rare, but very resistant, microscopic minerals, so called spinels, that once resided in micrometeorites that fell on Earth and became buried in sediments. Micrometeorites, up to two millimeters large, originate from colliding bodies in different parts of the asteroid belt between Mars and Jupiter. By reconstructing what types of asteroids that delivered micrometeorites at different times in the past, we can link in detail Earth’s history to otherwise hidden aspects of solar-system history. More on extraterrestrial spinels here.
In another project we search for meteorites, 1-20 cm large, that fell on a sea floor during the mid-Ordovician period, 470 Myr ago, in what is now southern Sweden. The meteorites are preserved in the sedimentary limestone as fossils, just like animal fossils. They are found during quarrying of the ancient sea floor for the production of e.g. sawed floor tiles. Since 1993 we have searched more than 40,000 m2 of the ancient sea floor for meteorites. More than 100 meteorites have been found, representing almost all fossil meteorites known to science. These meteorites tell a story about one of the most dramatic collisional events in the asteroid belt the last three billion years, the breakup of the >100 km large so called L-chondrite parent body. More on fossil meteorites here.
For the past two hundred years geologists have tended to look on the Earth as a more or less closed system. This general perception was changed by a major discovery by Walter and Luis Alvarez in the early 1980’s. By means of a thin iridium-rich clay layer distributed worldwide they were able to show that Earth’s Mesozoic fauna, including the dinosaurs, was wiped out 65 million years ago because Earth collided with an about 10 km large asteroid. Today we know that the impacting body created the ca. 200 km in diameter Chicxulub crater on the Yucatan peninsula, Mexico.