Rock-Solid Science: A 6-Mile-Wide Space Rock Did Wipe Out the Dinosaurs, Experts Say

By Smriti Rao | March 8, 2010 12:02 pm

taimpact_1Will we ever get a solid answer on what killed the dinosaurs? According to a new “K-T Boundary Dream Team” comprising of 41 international experts, including geophysicists and paleontologists, yes, the question has been settled: An asteroid is indeed to blame.

For years, scientists have argued over different theories of what killed the dinos–including one hypothesis that has gained ground recently, which suggests that massive volcanic activity in India’s Deccan Traps wiped them out 65 million years ago. However, the latest expert panel stuck to the asteroid theory, saying a massive impact wiped out the dinos and more than half of the Earth’s other species. The panel’s review was published in the journal Science.

After studying all the available data on the Cretaceous-Tertiary (K-T) mass extinction, the panel concluded that the catastrophic event was caused by a 6-mile-wide asteroid that struck Earth at an angle of 90 degrees and a speed of about 12.4 miles per second – about 20 times faster than a speeding bullet [Guardian]. The asteroid hit Chicxulub, Mexico, with a force one billion times more powerful than the atomic bomb at Hiroshima [Science Daily News].

The impact of the crash would have triggered large scale fires, landslides, earthquakes that measured 10 on the Richter scale, and subsequent tsunamis, scientists said. Debris loosened by the impact would have shrouded the planet, clouding the skies, causing a global darkness, and “killing off many species that couldn’t adapt to this hellish environment” [Science Daily News], according to study coauthor Joanna Morgan.

The scientists noted that the asteroid put an end to dinosaurs, the bird-like pterosaurs, and large marine reptiles, but it also marked a new beginning. Said study coauthor Gareth Collins: “Ironically, while this hellish day signalled the end of the 160 million year reign of the dinosaurs, it turned out to be a great day for mammals, who had lived in the shadow of the dinosaurs prior to this event. The KT extinction was a pivotal moment in Earth’s history, which ultimately paved the way for humans to become the dominant species on Earth” [Science Daily News].

The asteroid theory is far from new. The idea was first proposed by the father-son duo of Luis and Walter Alvarez three decades ago, when they found high levels of iridium in geological samples around the world. The element iridium is rare in the Earth’s crust but is common in asteroids, and can be found at asteroid impact sites. The current panel analyzed soil samples to find that immediately after the iridium layer, there is a dramatic decline in fossil abundance and species, indicating that the KT extinction followed very soon after the asteroid hit [Science Daily News].

The team also based their conclusions on “shocked” quartz. Quartz is shocked when it is hit very quickly by a huge force; shocked quartz is found only at asteroid impact locations and nuclear explosion sites. The abundance of shocked quartz in the rock layers associated with the KT boundary add further weight to the asteroid impact theory, the team declared.

Study coauthor Kirk Johnson says the team discarded the theory that large-scale volcanism made the dinosaurs extinct because the eruptions at the Deccan traps site started at least 400,000 years before the Chicxulub impact with no effect on life. The team traces the extinctions to within plus-or-minus 10,000 years of the impact 65.5 million years ago. “So we are back to where we started with the Alvarez hypothesis, a single, large, (6-mile-wide) impact,” Johnson says [USA Today].

Related Content:
80beats: Forget “The Asteroid”: Could Supervolcanoes Have Killed the Dinosaurs?
80beats: In the Permian Period, Erupting Super-Volcanoes May Have Killed Half the Planet
80beats: Dinosaurs Ruled the World Because They “Got Lucky,” Say Scientists
DISCOVER: Did an Asteroid Really Dust the Dinosaurs?
DISCOVER: When North America Burned explains how the asteroid could have set our continent on fire

Image: Nasa

CATEGORIZED UNDER: Environment, Space
  • CW

    This scientific debate is a good example in how real science is done and discussed. And I use this specific issue as an analogy with family/friends/co-workers to how climate change and AGW should be dealt with…robust discussion of the data/evidence and proper understanding of where the consensus exists.

  • m

    well said CW. further…nobody is threatened or bullied if they have an alternate view.

    these are the dark days of physics….with more articles like this, I start feeling more hope. heck, i might just renew my Discover subscription.

    time will tell.

  • Amit

    Well they should have considered this theory as well which was brought to light in Oct. 2009. There has been a lot of evidence in support of this additional information is relation to the Chicxulub hit.

  • CW

    Amit, there seem to be some debate on the Shiva crater:

    I’m not sure if it was reconciled or not though?

  • Robert Madewell

    Ironically, while this hellish day signalled the end of the 160 million year reign of the dinosaurs, it turned out to be a great day for mammals, who had lived in the shadow of the dinosaurs prior to this event.

    Also, a great day for birds. They seem to forget that.

  • amphiox

    “a great day” for the mammals and birds?!

    Fully half of all mammals species at the time were wiped out! The multituberculates were decimated and never recovered. The entire clade of enantiornithes were snuffed! Most of those that lived must have been reduced to a couple shell-shocked survivors who then had to endure years of cold and famine (after the dino carcass bonanza gave out). . . .

    This is what we call a “great” day?

    That’s taking “no pain, no gain” a little to the extreme, no?

  • jmk

    > amphiox Says:
    > “a great day” for the mammals and birds?!
    > [snip]
    > That’s taking “no pain, no gain” a little to the extreme, no?

    Er… no.
    It’s the event that allowed the mammals to become more than just a burrowing side-show, it allowed them to become the dominent form of life on the planet (if you don’t count numbers).

    The peak preditors anyway.

    And, of course, led eventually to you.

  • amphiox

    “It’s the event that allowed the mammals to become more than just a burrowing side-show”

    Except that for some 10 to 15 million years after the KT event, mammals remained small, burrowing side-shows, and the peak predators were giant birds (dinosaur descendents). Furthermore, the great diversification of mammals into the many lineages that included the ancestors of all the major living groups today happened 10 to 15 millions before the KT event (or something in that range)

    Many events allowed the mammals to eventually become dominant, and this was just one of them. It is actually an unprovable hypothesis contrary to fact to say that the KT extinction caused the eventual domination of mammals. We have no idea what might have happened if the KT event did not occur. For all we know, dinosaurs may have gone extinct anyways for other reasons 5 or 10 million years later, or become severely diminished, and mammals become dominant anyways. And to say that the KT event led to humans is no more informative than saying that the formation of the earth led to humans.

    I do not think that being the sole survivor of a global apocalypse counts as a “great” day, not even if it means your descendents will end up ruling the world 65 million years later.

    It was not a “great” day for anything.


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