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Are mass extinctions linked to severe impacts?

Some geologists believe that about 380 mn yrs ago, a rock from space smashed into Earth, wiping out a large fraction of life.

tech reviews Updated: Jun 26, 2003 13:15 IST

Is there a connection between mass extinctions and severe impacts? Some geologists think there is, believing that about 380 million years ago, a rock from space smashed into the Earth, wiping out a large fraction of life.

So far, the only candidate for a link is the meteor 65 million years ago that some believe helped exterminate the dinosaurs.

Signs of an earlier catastrophe coincide with a disappearance of many animals, according to Brooks Ellwood of Louisiana State University, Baton Rouge, USA, "It doesn't mean that the impact killed off the critters, but it's suggestive that it had something to do with it," he was quoted as saying by the journal Nature.

It's not known where a rock struck, although it's possible that traces of a crater might be found, Ellwood adds.

Other researchers agree that there was an impact around that time but feel the evidence for a mass extinction is much weaker.

Ellwood's team found that rocks in Morocco laid down about 380 million years ago bear a layer of sediment that resembles the debris from a cataclysmic explosion. The sediment has unusual magnetic properties and contains grains of quartz that seem to have experienced extreme stresses.

Around this time, about 40 per cent of marine animal groups vanished from the fossil record, says the team. Ellwood posits an asteroid slightly smaller than the 10-kilometre rock suspected of killing the dinosaurs.

The evidence for an impact is compelling, says geologist Paul Wignall of Leeds University, UK. And linking it to a mass extinction would be a major finding. "The potential lethality of impacts would be greatly increased," he says, the magazine reported.

But it's not clear how much disappeared around the time of the impact - the death toll may be far lower than Ellwood's team suggest, says Wignall. He thinks palaeontologists should search the rocks for a better picture of what happened at that time.

First Published: Jun 14, 2003 18:58 IST