Study: Dinosaurs Died Within Hours After Asteroid Hit

According to new research led by a University of Colorado at Boulder geophysicist, a giant asteroid that hit the coast of Mexico 65 million years ago probably incinerated all the large dinosaurs that were alive at the time in only a few hours, and only those organisms already sheltered in burrows or in water were left alive.

The six-mile-in-diameter asteroid is thought to have hit Chicxulub in the Yucatan, striking with the energy of 100 million megatons of TNT, said chief author and Researcher Doug Robertson of the department of geological sciences and the Cooperative Institute for Research in Environmental Sciences. The "heat pulse" caused by re-entering ejected matter would have reached around the globe, igniting fires and burning up all terrestrial organisms not sheltered in burrows or in water, he said.

A paper on the subject was published by Robertson in the May-June issue of the Bulletin of the Geological Society of America. Co-authors include CU-Boulder Professor Owen Toon, University of Wyoming Professors Malcolm McKenna and Jason Lillegraven and California Academy of Sciences Researcher Sylvia Hope.

"The kinetic energy of the ejected matter would have dissipated as heat in the upper atmosphere during re-entry, enough heat to make the normally blue sky turn red-hot for hours," said Robertson. Scientists have speculated for more than a decade that the entire surface of the Earth below would have been baked by the equivalent of a global oven set on broil.

The evidence of terrestrial ruin is compelling, said Robertson, noting that tiny spheres of melted rock are found in the Cretaceous-Tertiary, or KT, boundary around the globe. The spheres in the clay are remnants of the rocky masses that were vaporized and ejected into sub-orbital trajectories by the impact.

A nearly worldwide clay layer laced with soot and extra-terrestrial iridium also records the impact and global firestorm that followed the impact.

The spheres, the heat pulse and the soot all have been known for some time, but their implications for survival of organisms on land have not been explained well, said Robertson. Many scientists have been curious about how any animal species such as primitive birds, mammals and amphibians managed to survive the global disaster that killed off all the existing dinosaurs.

Robertson and colleagues have provided a new hypothesis for the differential pattern of survival among land vertebrates at the end of the Cretaceous. They have focused on the question of which groups of vertebrates were likely to have been sheltered underground or underwater at the time of the impact.

Their answer closely matches the observed patterns of survival. Pterosaurs and non-avian dinosaurs had no obvious adaptations for burrowing or swimming and became extinct. In contrast, the vertebrates that could burrow in holes or shelter in water -- mammals, birds, crocodilians, snakes, lizards, turtles and amphibians -- for the most part survived.

Terrestrial vertebrates that survived also were exposed to the secondary effects of a radically altered, inhospitable environment. "Future studies of early Paleocene events on land may be illuminated by this new view of the KT catastrophe," said Robertson.

Did ungulate mammals exist 65 myo? or did they evolve later?

From what I can find, The earliest ungulates go back 90 million years

Some birds do burrow, or take over existing burrows.

Yeah a few, But the vast majority do not and the vast majority of birds seemed to come through with no problem.

Plus even if Alligators and Frogs were underwater during the impact wouldn't they die when they came up to breath?

Many species of frog burrow into the mud and estivate during the summer or drought.

And many do not,

I can see some frogs and possibly some birds making it but all of them? No way!!

No particular reason 'gator eggs wouldn't survive, as you contend some dino eggs did. (KEWL!)

Because whether a gator is a male or female depends on the temperature the eggs are exposed to, So even if they survived the heat blast the global winter afterwards if it didn't kill them outright it would guarantee all gators would be born the same sex, So they would have gone extinct eventually anyhow.

And I don't contend that, the Geologist (of course) who found the fossils is guessing/wishing it. Geologist tend to make up all kinds of crazy things when they find something that conflicts with the Dino-Asteroid hypothesis (see the "Iridium is missing from the Chicxulub crater itself!!!!" link I posted before, The findings in that report clearly show that whatever happened at Chicxulub has nothing to do with the K-T yet the scientists refuses to even consider the possibility, They even go as far to say so in the paper, and instead they come up with all kinds of crazy explanations)

But it does bring up a good point in regards to this article, If gator eggs could survive the heat blast why couldn't buried Dino eggs around the world (not just in New Mexico) survive?

Just a guess - Bottom layer large/or low ejection angle (initial impact) spherules that settled out early. Mid layer turbite marls for the seiches of water sloshing in the Gulf of Mexico basin. Top layer lighter/high ejection angle (carbonate decomposition driven) ejecta.

No, The two spherule layers can not be from the same Asteroid.

Another picture of the duel sphere layer from the Geological society

Figure 3. El Penon, Mexico. Impact spherule layer at base of siliciclastic deposit is separated by a 15-20 cm thick sandy limestone. J-shaped burrows infilled with spherules are present in the sandy limestone and sandstone unit above. This indicates that both the spherule and sandstone units were deposited over an extended time period that excludes tsunami deposition.

I see most of the data supporting an impact and impact triggered vulcanism as consistent with the pattern of victims and survivors. I don't see anything that doesn't fit the hypothesis.

I see vulcanism being the reason or having a part in the demise of the Dinosaurs and other creatures but not an Asteroid.

Another thing to note is there is increasing evidence that the Chicxulub crater predates the end-Cretaceous mass extinction by about 300,000 years. (More info here and here).

We are clearly operating off subtly different data sets, and have reached differing conclusions. It will be fascinating to see where and how we converge on a consistent understanding.

We will, Once the Asteroid killed the Dinosaurs hypothesis is finally extinct.

Once again, excellent post. This is why I love FR!

You might then enjoy this article http://forteantimesmag.co.uk/articles/111_asteroid.shtml (Yeah, Yeah , I know what site it comes from but it's the best take on this "Controversy" I've seen)

It's very hard to dispute the evidence that we were clobbered by a very large impactor 65 million years ago, or that the implications for life would have been catastrophic. The only question is how catastrophic. There is no doubt at all that 70% of all species were wiped out.

Personally, when it comes to describing the physical effects of such a collision, such as broiling hot skies, sulphurous emissions, the release of vast quantities of carbon dioxide, etc., I prefer to listen to the physicists and geologists who know something about the subject, and NOT fossilists whose understanding of physics often doesn't even rise to the sophomore level. Their professional jealousy is obvious and rather pitiful; they should not allow it to get in the way of good science, but do.

However, when it comes to describing the fossil record of the extinction, how long it took, which species disappeared, etc., then I admit I would prefer to listen to the palaentologists (to the extent that their version of things does not contradict the hard physical evidence). They make many excellent points it seems to me. But their endless tantrums don't make it easy.

The debate is interesting and important. I just wish palaentologists would stop acting like a bunch of spoiled, pouting, foot-stomping brats. They had their century-long chance -- and then some -- at explaining the extinction of the dinosaurs but never even came close.

"According to new research led by a University of Colorado at Boulder geophysicist, a giant asteroid that hit the coast of Mexico 65 million years ago probably incinerated all the large dinosaurs that were alive at the time in only a few hours, and only those organisms already sheltered in burrows or in water were left alive.

Sorry for the late ping.

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