研究:地球每2700萬年遭受一次大滅絕

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.

‘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 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.

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.

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.

科學家稱，地球上的生命每隔2700萬年就會被滅絕一次，我們到下一次大滅絕之前還有約1600萬年時間。

科學家研究了過去5億年間地球上發生的所謂的“滅絕事件”，時間跨度是先前任何一項研究的兩倍。此次研究證實大滅絕的出現是有時間規律的。

來自堪薩斯大學和華盛頓史密森研究所的科學家們確信每2700萬年就會發生一次大滅絕事件，認爲可信度達99%。

20世紀80年代時科學家們認爲地球週期性的生物滅絕可能是由遙遠太空的涅墨西斯星球造成的，該星球和太陽很相似。

該理論認爲涅墨西斯星球每隔2700萬年會穿過奧爾特雲向地球發射一大批彗星。

奧爾特雲是一個由粉塵和冰組成的龐大雲帶，據信它距離太陽約一光年，許多穿越我們太陽系的彗星都來自那裏。

然而現在科學家稱大滅絕的週期性實際上證明涅墨西斯星球理論是錯誤的，因爲隨着時間的推移，在和其他星球的相互作用下，星球的運行軌跡會發生改變。

研究者稱：“引發涅墨西斯星球理論的化石資料現在卻成了對該理論不利的證據。”

上一次大滅絕事件是在1100萬年前發生的，當時地球上10%的居住者遭到滅絕。

這意味着到下一次毀滅性事件發生時還有約1600萬年的時間，儘管據圖表顯示這種大滅絕事件有時會提前1000萬年發生。

闖入地球的小行星一般被認爲是白堊－第三紀滅絕，即恐龍遭受大滅絕的主要原因之一。

那次毀滅性事件滅絕了地球上超過一半的物種，爲哺乳動物成爲地球上的首要物種掃清了道路。

那次大滅絕是由闖入地球的一顆巨型小行星造成的，形成了墨西哥希克蘇魯伯隕石坑。

這顆小行星直徑約15公里，據認爲它撞擊地球的力量比轟炸日本廣島的原子彈力量要大10億倍。

Vocabulary:

metronomic: 有節奏的

militate against sth.: to prevent something; to make it difficult for something to happen or exist（防止、阻礙某事的發生或存在）

asteroid: any one of the many small planets which go around the sun（小行星）

Cretaceous-Tertiary (KT) extinction: 白堊-第三紀滅絕事件，地球歷史上的一次大規模物種滅絕事件，發生於中生代白堊紀與新生代第三紀之間，約6550萬年前，滅絕了當時地球上的大部分動物與植物，含恐龍。