Asteroids Key to Biodiversity Boom?

Dec. 17, 2007 -- A shattered asteroid may have sprayed Earth with high-speed debris 470 million years ago and spurred one of the biggest bursts of biodiversity in Earth's history, rather than wiping life out.

The period of moderate to heavy meteorite bombardment appears to match the time at which many new species of animals evolved, called the Great Ordovician Biodiversification Event in the Middle Ordovician period, say geologists.

"Although this event represents the most intense phase of species radiation during the Palaeozoic era...the causes of this event remain elusive," report Birger Schmitz of the University of Lund, Sweden, and his colleagues in the December issue of Nature Geoscience.

Calling on meteorites as an explanation would seem to go against the more popular idea that impacts cause mass extinctions -- as is suspected to be the case 65 million years ago, when the dinosaurs and other organisms died off suddenly.

To make their argument, Schmitz and his team first point out research on meteorites that strongly suggests there was a major asteroid collision in the solar system about 470 million years ago.

Models suggest lots of debris, including large asteroid chunks, would be flying around the solar system for 10 to 30 million years after a big asteroid smashup, Schmitz explained. He and his colleagues have collected evidence of widespread impacts in rocks of that age on Earth.

"These asteroids were particularly prone to enter Earth-crossing orbits," Schmitz said.

That means, of course, they were quite prone to hitting Earth, and still are. The difference today, of course, is that there have been 470 million for Earth to -- hopefully -- sweep up the bigger chunks of asteroid debris.

Yet Earth is still being hit by smaller debris, known to meteorite researchers as the Flora family of asteroids, from the 470-million-year-ago asteroid event, Schmitz explained.