Life on Earth wiped out every 27 million years (but we've got about 16 million years until the next one)
By Niall Firth
Last updated at 1:50 AM on 14th July 2010
A comet striking Earth was behind the extinction of the dinosaurs彗星撞地球是恐龍滅絕的背後
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
The circled peaks on this graph from the paper are the mass extinctions while the dotted lines mark each 27 million years文件的這張圖週期見頂是大量滅絕時，而虛線標記每次2700萬年
‘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.
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.
http://www.dailymail.co.uk/sciencetech/article-1294372/Life-Earth-wiped-27-million-years.html
地球每2700萬年一次物種大滅絕 人類剩1600萬年
2010年07月14日14:48
來源：國際在線
據《每日郵報》報道，美國科學家近日經研究發現，地球每2700萬年要經歷一次物種大滅絕，而我們人類還剩下1600萬年的時間。
美國堪薩斯大學和華盛頓史密森學會的科學家將過去5億年間地球上發生的重大物種滅絕事件進行研究，並將其列成一張曲線圖，他們99%的肯定，在這漫長的5億年中，每2700萬年就要發生一次物種大滅絕，地球上的生物幾乎被“清空”，直到新的物種產生。
物種大滅絕的原因一直眾說紛紜。上世紀80年代，有科學家認為太陽有一個不發光的雙星尼彌西斯(復仇女神的名字)，它每過一段時間都會經過距太陽1光年的奧爾特星雲，大量的彗星會在這裡產生並撞向地球，給地球帶來可怕的災難。但是科學家的最新研究成果否定了這個假說，因為尼彌西斯的運行軌道會因其他星體的作用不斷改變，不可能遵循2700萬年的時間規律。
小行星撞擊地球是物種滅絕的主要原因之一。上一次大滅絕發生在1100萬年前，一顆巨大的隕石落在今天的墨西哥希克蘇魯伯附近，包括恐龍在內的大部分物種從地球上消失，為哺乳動物的蓬勃發展掃清了道路。
這就意味著下一次的大滅絕將發生在1600萬年后，當然這並不意味著人類可以高枕無憂了，因為曲線圖上顯示，物種大滅絕的時間偶爾會提前1000萬年左右。
http://env.people.com.cn/BIG5/12146346.html
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