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.
The geologists went hunting for evidence of the bombardment in fossil-bearing rocks of the same age in the Baltic Scandinavia and China. They found it in the form of a telltale rise and fall in levels of extraterrestrial chromite and osmium isotopes in the rocks.
The diversity of marine invertebrates called brachiopods
explodes in synchrony with the bombardment signal, they report.
"They make an interesting point — that diversification often takes off when you destabilize a community of organisms, and/or disrupt their habitat," said paleontologist Spenser Lucas, curator at the New Mexico Museum of Natural History and Science
. "Everybody has filled up eco-space and reached a stable ecosystem, and then impacting objects could upset the balance — opening niches, creating new niches, etc."
For this reason asteroid impacts should, in theory, both wipe out life and spur evolution. The two roles are not incompatible. It’s all a matter of timing and scale of the impacts.
On the other hand, said Lucas, a lot more evidence is needed to truly causally link the bombardment with the biodiversity event.
"I think Schmitz, et al., have an interesting idea worth further evaluation," said Lucas.
Via: Discovery Channel