Animals

Dinosaurs Might Have Gone Up in Smoke

Smoke and soot after an asteroid strike could have choked dinosaurs to death.

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A new theory on the extinction of dinosaurs and other animals at the end of the Cretaceous says that massive amounts of smoke and soot following the Chicxulub asteroid impact led to a devastating domino effect 66 million years ago.

The asteroid, which slammed into Earth at what is now Mexico's Yucatan Peninsula, not only immediately burnt some dinosaurs and other animals to a crisp, but also, according to the new study, hit the worst possible spot: an oil-rich area.

"The stratospheric soot was ejected from the oil-rich area by the asteroid impact and was spread globally," Kunio Kaiho of Tohoku University told Discovery News.

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"The soot aerosols caused sufficiently colder climates at mid–high latitudes and drought with milder cooling at low latitudes on land, in addition to causing limited cessation of photosynthesis in global oceans within a few months to two years after the impact, followed by surface-water cooling in global oceans in a few years."

In short, it was curtains for dinosaurs and many other animals shortly after the asteroid hit.

The scientists found that sediments in both locations for the target time period shared the same composition of combusted organic molecules.

"Therefore, this is the soot from the asteroid crash," Kaiho said.

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He and his team created a global climate model at the Meteorological Research Institute, and found that soot in the atmosphere after the asteroid impact would have produced colder climates at mid-high latitudes leading to the extinction of most species in these regions.

The soot, however, would have also caused droughts accompanied by mild cooling at lower latitudes that would have led to the extinction of dinosaurs, but would have allowed crocodiles and certain other animals to survive.

Image: Global climate change caused by soot aerosol following the Chicxulub asteroid strike. Credit: Kunio Kaiho

Water-dwelling species would have still had some resources. Small mammals and reptiles could have burrowed underground.

"The different habitats of the dinosaurs and small mammals and reptiles would have been key factors in determining their extinction or survival," he said.

Some dinosaurs, of course, did survive: birds.

As for the dinosaurs that were not immediately killed by the asteroid, the drastic climate change following the asteroid strike would have led to loss of soil moisture and vegetation in many areas.

Kaiho said that herbivorous dinosaurs would have consumed the ever-decreasing available plants, resulting in the eventual disappearance of such food, "similar to overgrazing leading to desertification today."

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As the plant-eating dinosaurs died out, so too did the remaining carnivorous dinosaurs, suggests the new paper.

In terms of dinosaurs literally going up in smoke, Manabu Sakamoto of the University of Reading, who has conducted other research on the dinosaur extinction event, told Discovery News, "Some dinosaurs definitely would have been instantly killed in the impact."

Sakamoto added that still other dinosaurs might have perished in a tsunami caused by the blast, but "the majority of the remaining dinosaurs would have likely starved to death as vegetation died out owing to the layer of ash that blacked out the sky (nuclear winter)."

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University of Florida geochemist Andrea Dutton authored another paper on the subject that was published last week in the journal Nature Communications. Her study suggested that volcanic activity prior to the asteroid hit was intense and likely contributed to climate change even before the fateful strike.

"The impact may have delivered the final blow, but it is clear that the ecosystem was under a lot of stress before that from the volcanic eruption," she told Discovery News.

She is not sure yet if the findings of Kaiho and his team align with those of her team.

She explained, "Warming from the eruption may have been countered by the cooling from the soot in the atmosphere, leaving not much of a temperature change -- if they canceled each other out. This is what we see at the boundary, not much temperature change, so what we need to do now is model these two events together to see if they match the data."