科学研究：地球每2700万年遭大灭绝

爱思英语编者按：科学家提出，地球上的生命每隔2700万年就会被灭绝一次，我们到下一次大灭绝之前还有约1600万年时间。科学家研究了过去5亿年间地球上发生的所谓的“灭绝事件”，时间跨度是先前任何一项研究的两倍。此次研究证实大灭绝的出现是有时间规律的。

Life on Earth is wiped out every 27 million years – and we have about 16 million years left until the next extinction, according to scientists.

Research into so-called "extinction events" for our planet over the past 500 million years  - twice as long as any previous studies  - has proved that they crop up with metronomic regularity.

Scientists from the University of Kansas and the Smithsonian Institute in Washington DC are 99 per cent confident that there are extinctions every 27 million years.

In the 1980s scientists believed that Earth’s regular extinctions could be the result of a distant dark twin of the Sun, called Nemesis.
The theory was that Nemesis crashed through the Oort cloud every 27 million years and sent a shower of comets in our direction.

The Oort cloud is a vast  belt of dust and ice that is believed to lie around one light year from the Sun and is the origin of many of the comets that pass through our solar system.

But now scientists claim that the regularity of the mass extinctions actually disproves the Nemesis theory because its orbit would have changed over time as it interacted with other stars.

The circled peaks on this graph from the paper are the mass extinctions while the dotted lines mark each 27 million years

‘Fossil data, which motivated the idea of Nemesis, now militate against it,’ say the researchers.’

The last extinction event, 11 million years ago, saw 10 per cent of the Earth’s inhabitants wiped out.

This means there is around 16million years until the next event takes place, although the graph shows that it occasionally the event takes place up to 10 million years early.

Asteroids crashing into the Earth are commonly believed to be one of the main reasons behind mass extinctions like that suffered by the dinosaurs  - the Cretaceous-Tertiary (KT) extinction. 更多信息请访问：http://www.24en.com/

The extinction wiped out more than half of all species on the planet clearing the way for mammals to become the dominant species on Earth.

The extinction was caused by a massive asteroid slamming into Earth at Chicxulub in Mexico.

The asteroid, which was around 15 kilometres wide, is believed to have hit Earth with a force one billion times more powerful than the atomic bomb at Hiroshima.