Millennia of chaos may have finally brought down the dinosaurs
It took not just a stray meteorite, but a pummeling on a scale barely imaginable to finish off the dinosaurs some 65 million years ago, researchers are reporting.
The Princeton University scientists tell of a double whammy of colossal volcanic eruptions and meteorite strikes whose effects pounded the mighty beasts into final submission.
Their new research, which portrays an Earth that was barely habitable for half a million years, weaves together elements of two leading theories on the mass extinction along with new details.
The result is one, epic tale of unrelenting chaos.
One of these previous theories, which has been the prevailing one, holds that a single large meteorite felled the great reptiles along with many other creatures. The other theory blames eruptions alone.
A Princeton research team found that a trail of tiny, dead marine organisms spanning half a million years offers a timeline linking the mass extinction to large-scale eruptions a primeval volcanic range once three times larger than France. The volcanoes, known as the Deccan traps, rose in western India.
A second research group uncovered traces near the Deccan Traps of a meteorite that they said may have been one of a series to strike the Earth around the time of the mass extinction. That, they said, could have pulled the plug on the few beleaguered survivors of thousands of years of volcano-fueled misery.
The first group reported this month in the Journal of the Geological Society of India that marine sediments from Deccan lava flows show that the population of a group of species known as planktonic foraminifera plunged almost to extinction in the thousands of years leading up to the dinosaur die-off. The foraminifera, which leaves tiny shells behind, are widely used to gauge the fallout of prehistoric catastrophes because they’re very sensitive to environmental changes, said the researchers, who were led by Princeton geoscientist Gerta Keller.
The destruction, they added, occurred in tandem with the largest eruption phase of the Deccan Traps — the second of three — when the volcanoes pumped the atmosphere full of climate-altering carbon dioxide and sulfur dioxide. A less severe third phase of Deccan activity is believed to have kept the Earth nearly uninhabitable for the next half a million years.
The other research group, based in Keller’s lab, found evidence in Indian sediment of a meteorite strike from the time of the mass extinction. This and others like it could have purged the already devastated landscape of the few, weakened species surviving the Deccan blasts, they said. That study appears in the October issue of the journal Earth and Planetary Science Letters.
The same sediment — located in Meghalaya, India, more than 600 miles east of the Deccan Traps — reveals Earth in this period as a harsh land of acid rain and erratic temperatures, the investigators claim.
Keller said the findings as a whole could put to rest the theory that the mass-extinction was due to just one large meteorite impact near Chicxulub in present-day Mexico. That impact — which occurred around the time of the second-phase Deccan eruptions — is thought to have been two million times more powerful than a hydrogen bomb and generated an enormous dust cloud and gases that radically changed the climate.
Keller has long held that the Chicxulub impact wasn’t bad enough to wipe out the scaly animals that had lorded it over the landscape. But the new work from her lab suggests the largest Deccan eruptions were that bad, or nearly so.
“Our work in Meghalaya and the Deccan Traps provides the first one-to-one correlation between the mass extinction and Deccan volcanism,” said Keller, who is lead author of the Geological Society paper and co-authored the other paper with lead author Brian Gertsch, now at the Massachusetts Institute of Technology. “But given the environmental instability caused by the massive Deccan eruptions, an impact could easily have killed off the few survivor species at the end of the Cretaceous” era, which coincides with the dinosaurs’ demise.
Vincent Courtillot, a geophysicist at Paris University Diderot who wasn’t involved in the Princeton work, called the findings an “impressive analysis.” Its significance is that it “was conducted in important sections near the volcanic action, and not thousands of kilometers [miles] away as had been the case previously,” said Courtillot, who led a team that reported in the Journal of Geophysical Research in 2009 that Deccan volcanism occurred in three phases.
The new findings, he added, “provide support for the idea that carbon and sulfur dioxide emissions were the principal agents of environmental change and stress.”
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Posted by Dinosaurs World at 7:27 PM