TINY meteorite fragments found in Antarctic rocks are the best evidence yet that the Earth鈥檚 worst ever mass extinction was caused by an impact from space.
Around 70 per cent of land species and more than 90 per cent of marine species, including trilobites, were wiped out at the end of the Permian period 250 million years ago. Experts haven鈥檛 been able to agree on what caused the destruction, although an ice age, volcanic eruption and an asteroid or comet impact have all been suggested.
Now Asish Basu of the University of Rochester in New York state and his colleagues have found 40 or so rock fragments up to 400 micrometres across that match the composition of 鈥淐M chondrites鈥�, which are among the most primitive meteorites. Basu argues that their presence in the 250-million-year-old rocks marks an impact (Science, vol 302, p 1388). He suspects a large asteroid or comet, although he still has some work to do to make a convincing case. There is no excess iridium in the rocks 鈥� its presence is usually a sign of an impact 鈥� and no one has found a matching crater.
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