Y: Yaël, did you hear that scientists have discovered evidence of another ancient asteroid impact?
D: You mean the asteroid that killed the dinosaurs?
Y: No, Don, this asteroid is much, much older than that. Dinosaurs lived about sixty‑five million years ago. This impact dates back about three and a half billion years.
D: Wow, Yaël. The earth was pretty young at that time. Wouldn't volcanic and other geologic activity have covered it over by now?
Y: There's still some ancient rock left in northwestern Australia. That's were scientists discovered tiny glass beads called spherules in a drilled core sample. The beads were formed from vaporized material from the asteroid impact. They also found elements such as platinum, nickel, and chromium which are found in the same proportions in asteroids. Not only that, they estimated the asteroid would have been ten to fifteen miles across, and would have created a crater hundreds of miles wide.
D: How do they know that?
Y: There is a relationship between the size of the spheres and the asteroid's size and velocity. It was so large, it would have triggered enormous earthquakes and tsunamis.
D: Why tsunamis?Y: The sediment layer was originally on the ocean floor. It was preserved between two volcanic layers which enabled scientists to date the glass beads. Material from the impact would have spread worldwide. The asteroid is the second oldest known to have hit the Earth, and one of the largest.