Earth hit by mass extinctions 'every 27m years'

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Life on Earth suffers catastrophic extinctions every 27 million years, according to researchers.

For at least the last 500 million years, say Adrian Melott, an astrophysicist at the University of Kansas, and Richard Bambach, a palaeontologist at the Smithsonian Institute, there has been a burst of extinctions every 27 million years.

Periodic mass extinctions have been posited before, and it has been suggested that it means the Sun has a huge, dark neighbour which orbits it every 27 million years, each time knocking a shower of comets out of the Oort Cloud at the fringes of the solar system and sending them crashing into Earth. This hypothetical dark satellite was called "Nemesis"
The extinctions range from utter catastrophe, devastating the majority of species on Earth, to smaller ones like the most recent, which destroyed 10 per cent of known species. And while they happen once every 27 million years, they do not arrive on cue, but up to 10 million years either side of the due date.

However, there is no immediate panic. The last such event took place 10 million years ago, so there should be plenty of time to work out what is going on before the next one comes....

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