The best telltale sign of a meteor strike is the impact crater. But unlike the Moon, Earth’s plate tectonics and weathering have a way of making craters disappear over time. Add in some vegetation growth and voila! What craters?

There are, of course, exceptions in places where there is no vegetation and little weathering or tectonics, such as Meteor Crater in Arizona. That’s one major exception, though. To find the crater caused by the impact that killed the dinosaurs required sonar data from the Caribbean and satellite data of the Yucatan plus ground maps of the cenotes that outlined some of the crater’s shape. Not exactly the easiest crater to locate.

Now, however, a team working in Chile’s Atacama Desert, the home of the ALMA telescope, has found a new method of locating evidence for an ancient meteor strike. They have found centimeter-sized nodules made of glass, created at high temperatures and pressures, scattered over hundreds of kilometers in that desert. These were likely formed when an iron-rich meteorite hit the Earth about eight million years ago.

Oh, and I love the name of these nodules: atacamaites. Thank you, geologists.

Atacamaites are a type of impact glass. They’re formed when a large meteor hits the planet with enough force to basically melt the rocks on the surface, throwing the molten material into the air where the cooler temps cause the liquid fragments to resolidify quickly. With no time to form and grow crystals, the resulting rocks are considered glass, and they provide crucial evidence for past meteor strikes. They’re still difficult to find. Only five other groups were found prior to this one in Chile.

The evidence of this strike was first found in 2007 by electrical engineer Michael Warner, who worked out of NOIRLab in La Serena, Chile. He and his son then found some more a few years later, and they sent the samples off to geologist Jérôme Gattacceca at the National Centre for Scientific Research in France. Gattacceca had analyzed meteorites for Warner previously, and in this case, he determined that the samples were impact glass; he has since brought colleagues to the Atacama Desert to help look for more evidence, and they have found over 23,000 atacamaites since 2014. A careful analysis of several of these nodules has revealed that they are about 5% by weight made of extraterrestrial stuff like meteoritic iron, nickel, and cobalt.

As the team reported in Earth and Planetary Science Letters, the impact occurred about eight million years ago, but they haven’t yet found any evidence of a crater. It’s possible that erosion is the culprit; however, the team is continuing to search satellite data and plans to go back to the region to look for the crater again. We’ll keep you updated on their findings here on Daily Space.

More Information

Glassy Nodules Pinpoint a Meteorite Impact (Eos)

“A 650 km2 Miocene strewnfield of splash-form impact glasses in the Atacama Desert, Chile,” J. Gattacceca et al., 2021 June 21, Earth and Planetary Science Letters