Over the years, scientists have debated the cause of the mass extinction that wiped out the dinosaurs 65 million years ago. Now, a panel of 41 international experts says it’s official: a massive asteroid around 15 kilometers wide slamming into Earth at Chicxulub, Mexico is the culprit. After surveying a wide variety of evidence for the competing theories, the panel said the telling evidence was the structures preserved in the interior of the crater. Computer models predicted how much rock was vaporized or ejected by the impact. “Our work lets us visualize the astonishing events of the few minutes after impact,” said Dr. Penny Barton, who led the group. “The front of the asteroid hit the Earth while the far side was still out in the upper atmosphere, punching a hole though the Earth’s atmosphere.”
The Cretaceous-Paleogene extinction was one of the biggest in earth’s history and geologic evidence of the impact has been discovered in rock layers from this time period, around the world. While the impact is widely accepted as the cause for the mass extinction, some critics disagreed, saying, for example, that the microfossils from the Gulf of Mexico show that the impact occurred well before the extinction and could not have been its primary cause.
The massive volcanism that produced the Deccan traps of India around this time has also been proposed as the main cause of the extinction. But in the panel’s review, the computer models synthesized the geologic evidence that support the impact hypothesis. The models showed that such an impact would have instantly caused devastating shock waves, a large heat pulse and tsunamis around the globe.
Moreover, a release of larger amounts of dust, debris and gases would have led to a prolonged cooling of Earth’s surface, low light levels and ocean acidification that would have decimated photosynthesizing plants and the species that relied on them.
The asteroid is believed to have hit Earth with a force one billion times more powerful than the atomic bomb at Hiroshima. It would have blasted material at high velocity into the atmosphere, triggering a chain of events that caused a global winter, wiping out much of life on Earth in a matter of days.
“As the asteroid vaporized explosively,” said Barton, from the University of Cambridge in the UK, “it created a crater 30 km deep and 100 km across, with sides as high as the Himalayas. However within only two minutes the sides collapsed inwards and the deepest parts of the crater rebounded upwards to leave a wide, shallow hollow.
“These terrifying events led to darkness and a global winter, resulting in the extinction of more than 70% of known species. The tiny shrew-like mammals which were around at that time proved better adapted to survival than the cumbersome dinosaurs, and the removal of these dominant animals paved the way for the radiation of the mammals and eventual emergence of humans on Earth.”
The team’s paper was published in the journal Science.
Sources: University of Cambridge