Meteorite collision wiped out species 251 million years ago

By STEVE CONNORSteve Connor

A massive impact with a giant meteorite caused the worst day in the history of life on Earth - the day when the greatest number of species became extinct. Scientists have found the "smoking gun" that points to a collision with a chunk of space rock at least seven miles wide as the cause of the greatest mass extinction of all time.


If the evidence is confirmed by other scientists it would be the second time that a giant meteorite has been shown to be the cause of a sudden and otherwise inexplicable mass death of animals and plants across the entire planet.

Most scientists agree that a giant meteorite killed off the dinosaurs some 65 million years ago but a team of geologists have now suggested that an earlier meteorite caused an even bigger mass extinction when it hit the Earth about 251 million years ago. This was the precise boundary between the Permian and Triassic geological periods.

Asish Basu and colleagues of Rochester University in New York believe they have found microscopic fragments of the killer meteorite buried within the rock layer dating to this violent moment in history.

"An ancient meteorite body, one from the days when the solar system was still forming, struck the Earth 251 million years ago. This was possibly the worst possible day in the history of life on Earth," Dr Basu said.

The Earth was then a very different place, with most of the landmass forming a giant supercontinent called Pangea. Lumbering, four-legged reptiles dominated the land and giant fern trees grew in abundance until they were suddenly wiped out in an event known as "the great dying".

During the Permian Period, the Earth teemed with strange and exotic lifeforms, such as giant sharks and reptiles, dinosaurs, seabed-dwelling creatures called trilobites and lush vegetation.

It is estimated that during the Permian-Triassic (P-T) boundary, about 90 per cent of the marine species and 70 per cent of the land species vanished in the geological equivalent of an instant - the greatest of all the five mass extinctions that are recorded by the fossil record.

Luan Becker of the University of California, Santa Barbara, a member of the team, said: "This was the mother of all extinctions. What makes is remarkable is that virtually all marine life and a good portion of land life forms were eliminated in a very short period."

Just as the demise of the dinosaurs 65 million years ago allowed the rise of the mammals, the demise of the dominant species 251 million years ago allowed the dinosaurs to dominate the land.

Dr Basu's team has found dozens of microscopic grains of the meteorite within the P-T boundary layer which he has excavated in Antarctica. He has found an iron alloy in the fragments that does not occur naturally on Earth and matched them with similar meteorite fragments found within the same geological layer excavated in China and Japan.

"At the end of the Permian era, Antarctica was close to its present position as the southernmost part of the ancient supercontinent, Pangea, while south China was at the equator and Japan was to the north of the equator," Dr Basu said.

"Such a wide, global distribution of these metal [meteorite] grains in the P/T boundary strongly suggests that these grains mark a major impact of a celestial body at that time," he said.

It is impossible to estimate the exact size of the meteorite but it must have been at least as big at the one that killed off the dinosaurs, which is calculated to have been about 10 kilometres (6.2 miles) wide.

"The effect of the impact was even bigger and more catastrophic than the one that killed off the dinosaurs," Dr Basu said.

The scientists found the meteorite fragments in an area of Antarctica called Graphite Peak but they believe that the actual site of the impact was a few thousand kilometres away, possibly in what is now western Australia.

- INDEPENDENT