研究：地球物种每2700万年灭绝一次

Life on Earth is wiped out every 27 million years – and we have about 16 million years left until the next extinction¹, according to scientists.

科学家称，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。

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（突然出现） with metronomic（有节奏的） regularity².

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 Nemesis³（报应，天罚） .

The theory was that Nemesis crashed through the Oort cloud every 27 million years and sent a shower of comets（彗星） 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.

‘Fossil data, which motivated the idea of Nemesis, now militate against（产生不利影响） it,’ say the researchers.

The last extinction event, 11 million years ago, saw 10 per cent of the Earth’s inhabitants wiped out（精疲力竭的） .

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

Asteroids⁵（小行星） crashing into the Earth are commonly believed to be one of the main reasons behind mass extinctions like that suffered by the dinosaurs⁶（恐龙） - the Cretaceous-Tertiary (KT) extinction.

The extinction wiped out more than half of all species on the planet clearing the way for mammals to become the dominant⁷ species（优势物种） on Earth.

The extinction was caused by a massive asteroid⁴ slamming（抨击） 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.