天体碰撞导致恐龙灭绝的理论被确证

An international panel of experts has strongly endorsed evidence that a space impact was behind the mass extinction event that killed off the dinosaurs.

一个国际专家小组强烈支持一场太空大碰撞导致地球上恐龙灭绝的理论。

The dinosaurs were one of many groups to go extinct

They reached the consensus（一致，舆论） after conducting the most wide-ranging analysis yet of the evidence.

Writing in Science journal, they rule out alternative theories such as large-scale volcanism（火山作用） .

The analysis has been discussed at the 41st Lunar and Planetary Science Conference (LPSC) in the US.

A panel of 41 international experts reviewed 20 years' worth of research to determine the cause of the Cretaceous（白垩纪） -Tertiary（第三纪） (K-T) mass extinction, around 65 million years ago.

The extinction wiped out more than half of all species on the planet, including the dinosaurs, bird-like pterosaurs（飞龙目） and large marine reptiles（爬行类） , clearing the way for mammals（哺乳类） to become the dominant species on Earth.

Their review of the evidence shows that the extinction was caused by a massive asteroid（小行星） or comet smashing（猛撞） into Earth at Chicxulub on Mexico's Yucatan Peninsula.

'Global winter'

When the 10km-15km space rock struck the Yucatan, the explosive energy released was equivalent to 100 trillion tonnes of TNT（三硝基甲苯） - over a billion times more explosive than the bombs dropped on Hiroshima and Nagasaki.

The huge crater（弹坑，火山口） that remains from the event is some 180km in diameter and surrounded by a circular fault about 240km in diameter.

"You can actually trace debris right up to the rim（边缘） of the crater from across the world," Co-author Dr David Kring, from the Lunar and Planetary Institute in Houston, told BBC News.

"You can start in Europe, cross the Atlantic and it just thickens as you approach the Chicxulub impact crater."

In the new study, scientists examined the work of palaeontologists, geochemists（地球化学家） , climate modellers, geophysicists（地球物理学者） and sedimentologists who have been gathering evidence about the K-T extinction.

They conclude that the Chicxulub space impact is the only plausible explanation for the devastation evident in geological records.

The initial impact would have triggered large-scale fires, huge earthquakes, and continental landslides which generated tsunamis.

Dr Gareth Collins, one of the review's co-authors from Imperial College London, said the asteroid hit Earth "20 times faster than a speeding bullet".

He added: "The explosion of hot rock and gas would have looked like a huge ball of fire on the horizon, grilling（拷问，审问） any living creature in the immediate vicinity（紧邻） that couldn't find shelter."