But this fossil meteorite shows us that they were arriving on Earth long before humans.
Thanks to Brilliant for supporting this SciShow video! As a SciShow viewer, you can keep building your STEM skills with a 30 day free trial and 20% off an annual premium subscription. In 1982, scientists set sail aboard a ship with a giant drill stuck on the back of it. Their goal? To extract columns of seafloor, and let layers of sediment tell a geologic bedtime story. But nestled within a layer around 66 million years old, they found something completely unexpected. They found a fossil, just two and a half millimeters across. But it wasn’t one of the last dinosaurs, or any of the other life forms wiped out when a massive space rock hit the Earth. It was a fossil of a rock! A rock that came from space. It could be a fragment of that deadly meteorite. And as one of the first fossilized meteorites ever discovered, it has shown us a new way to learn about our planet’s past. The first confirmed fossil meteorite was found in 1952, but it wasn’t until 1979 that scientists actually took a closer look and figured out what it was. As of 2017, 115 fossil meteorites have been discovered, the majority of which have come from the Thorsberg limestone quarry in Sweden. This quarry is a great source of fossil meteorites due to its slow formation, which began as an ocean floor over 470 million years ago, and built up layers of sediment 10 times slower than usual. This gave meteorites more time to fall into the ocean and get caught in the growing limestone layers.
The fossil meteorites tell the story of a massive collision that took place in the solar system’s asteroid belt between Mars and Jupiter roughly 470 million years ago - the largest known asteroid belt crash of the past 3 billion years. Some of the debris quickly made its way to Earth, causing a storm of space rocks to rain down on the planet over 200 million years before the dinosaurs showed up.
This space rock storm hasn’t stopped yet - around a quarter of the meteorites falling today have the same composition, suggesting that they are remnants of that event. Scientists believe that the ancient barrage could have given evolution a helping hand, as the fossil record shows an acceleration in marine life evolution around that time, known as the Great Ordovician Biodiversification Event.
The Thorsberg quarry workers have been methodically searching in their worksite since 1995, and one scientist even made it a habit of crawling around in public buildings with limestone floors in Sweden, searching for ones that slipped out of the quarry unnoticed.
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