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Scientists Come to a Conclusion: Asteroid Killed the Dinosaurs

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


Nancy Atkinson is currently Universe Today's Contributing Editor. Previously she served as UT's Senior Editor and lead writer, and has worked with Astronomy Cast and 365 Days of Astronomy. Nancy is also a NASA/JPL Solar System Ambassador.

Comments on this entry are closed.

  • sneakypete77 March 5, 2010, 10:08 AM

    It’s interesting to contemplate just how “useful” mass extinctions are to jump-starting species down new paths of evolution. Maybe some mass extinctions are good, maybe some are bad in the grand scheme…I’m not sure.

  • Starhunter March 5, 2010, 6:08 PM

    Very interesting, isn’t possible the volcano could have triggered by the impact or it was already in process, its a puzzle we’ll never be able to answer for sure , just like the how the moon came to be.

  • Excalibur March 5, 2010, 10:16 AM

    Well Spoodle58, i will try to make sense of what you just said.

    1. 65 Ma ago an astreoid hits the earth
    2. Between 65 Ma ago and 60 Ma ago the population of dinosaurs drop from 30 to 7.
    3. The asteroid in 1. hit before the dinosaurs was already basically extinct. Well, duh, it seems to have started the entire scenario.

    Something hints to me that you have confused past timeline, 60 Ma ago is after 65 Ma ago, not before.

  • JoeTO March 5, 2010, 12:43 PM

    Could be 65 Million BC. :)

  • Lawrence B. Crowell March 5, 2010, 4:52 PM

    I have a question. Maybe somebody has looked into this. When the asteroid hit huge shock waves, or seismic waves went through the Earth. There is an effective lensing due to the acoustical propagation of various layers in the Earth. These would have partially focused a lot of this energy on the antipodal side of the Earth, or along a line of the asteroid’s trajectory. This then might have caused a pretty serious upheaval there. The Deccan flats or volcanoes also blew their stack around this time. The question is whether these might have been caused by this event.

    As for dinosaurs going extinct, the line of microraptors which came about in the early Cretaceous did survive as birds. In fact by the end of the Cretaceous it appears these already constituted the largest number of species of dinosaurs.


  • Bravehart March 5, 2010, 7:38 PM

    Very interesting, but is this called speculation
    is it not? Any one notice the time corrolation
    of the release of this ” DEFENITE” conclusion
    and the recent quake in Chili?
    If in accordense with this paper the Earth
    MUST have moved its trajectory, not by an inch, but by several Kilometers and if an 8.8
    Rigther can cause a shift in the Earth axis?
    Then what would the shift in axis and the rotational speed be at such an impact?
    If this would happen today, most live forms
    would perris!
    I convinced that they droped the ball on this one!
    P.S. please elevate from the debate of who came first, the chicken or the egg?

  • Matt S. March 6, 2010, 3:36 AM

    Any one notice the time corrolation
    of the release of this ” DEFENITE” conclusion
    and the recent quake in Chili?

    Which is entirely unrelated. Is this some weird attempt at post-hoc-ergo-propter hoc? As if those who conducted the review of the literature started working after the earth quake.

    So what’s the point you’re trying to make? The impact couldn’t happen because, well, “most live [sic] forms” would be in peril? That doesn’t make sense. Or are you just expressing your distress that if this were to happen again we’d be on our way out?

    And actually, while an asteroid impact can alter the axial tilt of a planet the size of earth (not very significantly though), the TRAJECTORY will remain almost the same. The size difference, 12km vs. 12000km, is just too huge for that.

  • Lawrence B. Crowell March 6, 2010, 3:49 AM

    I thought about this a few weeks ago in fact. It is of course the case there was already was a tectonic plate boundary present. There may be been volcanism there. India at that time was detached from Asia and more tropical, putting it pretty darn close to the antipodal point of the Chicxulub impact point. Yet the huge seismic wave focused near this region might have caused enough of a rupture or dislocation to hyperdrive volcanism at the Deccan traps. I thought about writing a computer program to model this problem, but I have to carve out considerable amount of time to do that. If this is the case it was a gift from heaven that kept on giving, where subsequent decades of intense volcanism would have prolonged and compounded the change to the planetary environment.

    I suspect the main cause for extinction was the chemical change in the environment. The large amount of sulfides released in the atmosphere would have acidified oceans and changed the background chemistry life had adapted to. It is worth pondering how we humans might be engineering such an change now.


  • Spoodle58 March 6, 2010, 7:33 AM

    @ Excalibur

    Sorry typo, glad you caught it.

    It should read as.
    The fossil record shows us that dinosaur species types had dropped from 30 plus to about 7 species types from 70 million years ago to 65 million years ago.

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