Debris from ancient asteroid explosion still peppering our planet

Extreme cj Times

At a time when terrestrial plant life was just beginning to take hold here on Earth some 466 million years ago, a massive asteroid collision happened someplace nearby. We don’t know much about the nature of the original objects that collided, except that one of them was about the size of Connecticut. The fragments that have since rained down on Earth are actually quite well studied — they’re still the most common type of meteorites landing here. Astronomers have long felt this event masks the true nature of space rocks, so a team at the University of Chicago has been trying to filter out these objects to see what’s left. They describe it as finding a needle in a haystack.

The debris from this ancient collision comes from a group of meteorites known as chondrites, sometimes called undifferentiated. They’re essentially clumps of rock, dust, and metal. The other main meteorite composition are called achondrites (or differentiated). They’re stony meteorites that come from larger bodies like the asteroid Vesta (or a planet). There are also various ungrouped meteorites that don’t fit cleanly into any one category.

It’s been a bit of a mystery by the composition of meteorites on Earth don’t match the composition of the asteroid belt, and now we’ve got a better idea why. The huge collision 466 million years ago contaminated Earth with so many chondrite meteorites that it makes it harder to get an accurate picture of the solar system’s actual makeup. The University of Chicago team led by cosmochemist Philipp Heck were able to find ancient meteorite fragments from before the chondrite-forming event.


Finding a whole meteorite that survived 500 million years unchanged would be extremely difficult, so the team focused on fragments. They collected nearly 600 pounds of rock from formations in China, Sweden, and Russia for analysis. While these samples were collected on land, the rocks they came from were once on the bottom of an ancient ocean. Finding the meteorites in all that terrestrial rock was going to be tough,so the team took a bit of a shortcut. As Heck says, they burned the haystack. A strong acid was used to dissolve the rock. This left a total of 41 tiny meteorite fragments with the proper oxygen isotope ratio to indicate they were from before the chondrite event.

Analysis of the ancient meteorites shows that the achondrite meteorites that are so uncommon now relative to chondrites were about 100 times more common in the past. This data can be compared with spectrographic studies of the solar system, allowing scientists to study material from objects we can’t currently visit.

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