The impact occurred 66 million years ago and the crater is 150 miles wide. You wouldn't be able to see it without satellite images and 66 million years is a long time for corrosion and plant life to disguise the crater.
Photograph by Joel Sartore, National Geographic Creative
Published July 28, 2014
Wrong place. Wrong time. Dinosaurs didn't have to die off, but the space impact that blasted the Earth some 66 million years ago arrived at a most inopportune moment for the long-time rulers of the planet, according to a report released Monday.
There's never a good time for an asteroid impact, of course, but debates have roiled among scholars for decades over whether volcanoes or a long-running decline in species may have played a bigger role in the demise of the dinosaurs. (Related: "Dinosaurs 101.")
Now a Biological Reviews journal report concludes that the asteroid or comet that created the Yucatan's Chicxulub crater was indeed the likely leading culprit. Other factors, most notably a vulnerable sub-population of big plant eaters, essentially left the dinosaurs ripe for the asteroid wipe-out.
"If the asteroid hit five million years later or earlier, the dinosaurs might still be around," says paleontologist Stephen Brusatte of the United Kingdom's University of Edinburgh, a member of the report panel that included experts from leading dinosaur museums and universities worldwide. "An impact would have been horrible for them, but they had survived dips and dives for more than 150 million years," he says.
At least six miles (ten kilometers) wide, the Chicxulub impact object left a crater some 110 to 180 miles (177 to 290 kilometers) wide and 12 miles (19 kilometers) deep beneath Mexico's Yucatan peninsula and the Gulf of Mexico.
Since Nobel Prize winning physicist Luis Alvarez and colleagues first suggested the asteroid explanation for the death of the dinosaurs in 1980, scholars have debated its role, over time coming to what the review authors are calling a consensus on its central place in the dinosaur doomsday.
"It's pretty remarkable to have paleontologists agree on anything," says paleontologist Richard Butler of the United Kingdom's University of Birmingham, a review author. "Most would now agree the impact played the largest role."
Birds are now thought to be the only dinosaur survivors of the space impact's destruction, which ended roughly 160 million years of animal kingdom domination by dinosaurs, including through other mass extinctions. (Related: "Siberian Discovery Suggest Almost All Dinosaurs Were Feathered.")
"What has really changed is that we now have a great deal of evidence from fossils, from dating and from geology, of what dinosaurs were doing," Butler says. "Were they all dwindling away before the impact and would have disappeared anyway? They weren't. The evidence is that the impact did it."
Dinosaurs disappeared during the era of the Tyrannosaurus Rex and Triceratops well known from museum exhibits, the Late Cretaceous. While the overall diversity of dinosaur species at this time wasn't broadly decreasing, the review finds that it was among one key group-big plant eaters such as the duck-billed dinosaurs that were the prey for the big carnivorous dinosaurs.
"There were just as many individual dinosaurs, but fewer species, and they looked more similar," Butler says, pointing to ecological analyses cited in the review. "This loss of diversity among these key species is the best mechanism we have for explaining why they were more prone to a collapse."
Essentially, the review suggests that the big plant eaters, the horned ceratops and duck-billed hadrosaurs, were keystone species in dinosaur ecology. Their species-wide similarity and lack of diversity pointed to dinosaurs having fewer places of refuge, no alternative prey and fewer adaptive characteristics to rely on, once the asteroid hit.
The impact plunged the Earth into a global firestorm followed by decades of "impact winter," triggering the loss of perhaps 75 percent of all species worldwide, including the non-avian dinosaurs.
"In any ecosystem when you remove links to key species, that community has problems," Butler says. An asteroid was just a really big problem that came at a bad time, he says.
Good Times, Bad Times
Dinosaurs had other troubles around 66 million years ago. A period of intense volcanism seems to have started several hundred thousand years before the impact. Climate temperatures swiftly cycled up and down, perhaps in response.
And a period of lowered sea level removed inland seas such as one that once covered the middle of North America and provided marshy homes for diverse groups of disconnected dinosaurs. Land bridges forming in the era may have connected formerly isolated populations, spurring a uniformity among species of large plant eaters.
The massive numbers of volcanoes preceding the Chicxulub impact came from the "Deccan Traps", a 200,000-square-mile (518,000-square-kilometer) mountainous region in central India. Princeton geophysicist Gerta Keller, who has long argued these eruptions played a bigger role in extinguishing the dinosaurs, disagrees with the asteroid "consensus" view in the Biological Reviews report.
"Compared with this volcanic catastrophe, the Chicxulub impact is a much lesser catastrophe," Keller says, by email. Each one of the eruptions would have had the climate impact of the asteroid, she suggests, adding that perhaps 30 to 100 eruptions took place. "Deccan volcanism is clearly the main catastrophe leading to the mass extinction."
However, Brusatte says that dinosaur fossils are still evident after the era of the Deccan eruptions, but not after the impact. A May Proceedings of the National Academy of Sciences journal study concluded that the impact caused a global winter lasting for decades, "a key contributory element in the extinctions of many biological clades, including the dinosaurs."
Although dinosaur researchers now know of many more species ("about one new one a week is being reported," Brusatte says) than they did in 1980, their analysis still largely relies on North American fossils, which the review concedes is one weak point in the analysis.
"We need to find more fossils outside North America," Brusatte says. "But we do think we have enough information now to be confident that the asteroid impact was the primary factor in the extinction of dinosaurs."
"One question that always gets asked is what would have happened if the asteroid hadn't hit," Butler says. "Given how successful the dinosaurs were, able to return to normal after past dips, it's likely they would still be here. And we wouldn't."
Correction: The article originally misstated the era of the last nonavian dinosaurs; it was the late Cretaceous.
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Fact is there is another consensus, that untold numbers of dinosaur species survived the asteroid for millemia. What hasn't begun to be figured out is how, and what then did them in.
I'm incredibly tired of facile review papers that contribute nothing new to the field getting so much popular press.
more wild assed speculation by leftist pseudo scientists with a political agenda. where are the real scientists.
Kind of miss the days when the primary explanation for the demise of the dinosaurs was that their own farts did them in; in that: the flatulence of large herbivores caused a massive increase in atmospheric methane; which, in turn, caused a greenhouse effect... .
considering this and the other article on crow intelligence, I'm sure we would've had "Crow sapiens" by now if their hadn't been a meteor.
July 28 Come on now. I saw a documentary movie filmed recently that has lots dinosaurs running around at a Park on a remote island out in the Pacific ocean somewhere off the coast of Centeral America. The Park Corporation is planning to get approval for helecopter rides out there and overnight hotel accommodations. I bet cruise ship companies will get to send passengers for island day trip tours real soon. So, it's clear lots of dinasoars lived on after the asteroid hit. That asteroid hit way on the other side of Mexico, not in the Pacific Ocean where plenty of dinasoars still live. We don't see 'em much cuz they don't know how to swim good and even after all these years they never learned to build boats. I figure they never thought there was any other place to go except stay on their own island. They are real big, some of them, but they aren't real smart.
Not to discount volcanoes and climate change but short of runaway greenhouse affects (like Venus) no volcano, super volcanoes or series of volcanoes is going to even begin to rival the shear destruction of a dense 6 mile wide astriod.
As far away as the future great lakes region you would have enough over pressure to shred and land animal. The entire globe would have experience surface temperature exceeding 1200 f for a short period of time as a result of atmospheric friction from derbies reentering the atmosphere. And after that you would have deal with the end result of having nearly everything on the surface burned by a global firestorm.
Quite possibly if the dinosaurs hadn't have disappeared the little rodents that led to humans may never have risen to prominence. Some of the smaller dinos may have developed survival talents leading to a completely different supreme life form. The opposable thumb theory doesn't hold a lot of water when you consider monkeys have had thumbs as long as humans but never rose above flinging feces.
In the first paragraph after the first subhead, you write that the dinosaurs disappeared at the end of the Late Jurassic; it was actually the Late Cretaceous.
@Roiikka-Ta P Globetrotter You did not read far did you?
@William Brower If you were to assume that evolution is linear and produces the same results recurring...but that is not the case.
@A J ...Attention seekers, what can you do?
@james george Where is the intelligence in the clearly demented and anti-scientific extreme right?
@james george Sorry, james, but you have no idea what you're talking about. I have a degree in this field and can substantively criticize the paper.
I can also tell you that your comment is complete clueless bull.
Have you no shame? Once upon a time in this country it was considered rude to open your mouth when you don't know wtf you are talking about. The blowhard generation, that's what I call people like you, changed all of that.
Calling these authors "leftist pseudo scientists" when you know diddly squat about them or the science is just shameful and embarrassing. It's the kind of behavior that could be forgiven... in a kindergartner. But any person capable of correctly spelling the word "scientist" is passed the point where common sense and reason should be developed enough for them to know to keep their mouth shut when they're clueless on a subject.
@C. Dufour Fact is crows are smarter than human babies at least, and some human adult typists.
According to Everett's relative state model (local version of multiverse) all histories are in fact get into actualization, less probable plots are less numerous more probable plots are more... ( such probabilistic implications of Everett model has been developed not long ago). Thus, reptilians are out there for sure as well as all sorts of mammalians, unlikely reptilians are interested in our branch of existence though .... ;o)
@Will Lickmanouver must be a different article, mine says Cretaceous.
@Wayne Wright my god wayne. get a grip.
@Wayne Wright You have an error in your logic.
@Robert Evans yep, you are right. will make a correction, thanks for spotting my mistake
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