Free the Asteroid! (It Didn't Kill the Dinosaurs)

Ask your favorite 6-year-olds what doomed the last dinosaurs 65 million years ago, and unless they don’t know a Troodon from a Triceratops they’ll tell you it was a killer asteroid. This idea, first proposed in 1980 and widely adopted a decade later, has entered the public consciousness like few others in science. Too bad it doesn’t have nearly the credibility among geoscientists as it does in local sandboxes and Hollywood: evidence keeps emerging that the asteroid was framed.

Instead, a series of titanic volcanic eruptions in India may have wiped out T. rex and his friends (and prey). That idea has been around for a while, but today paleontologist Gerta Keller, who has long been dubious about the asteroid theory, will unveil the strongest evidence yet that scientists convicted the wrong perp. In a study presented at the annual meeting of the Geological Society of America in Denver, she will announce that the volcanic eruptions that created the enormous Deccan Traps lava beds in India peaked at just the right time to explain the dinos’ demise—releasing what she and colleagues estimate was ten times more climate-altering gases (mostly carbon dioxide and sulphur dioxide) into the atmosphere than the asteroid impact.

Previous research had dated the volcanic eruptions to within 800,000, then 300,000, years of the worldwide extinction whose highest-profile victims were the dinosaurs but which also killed some half of all species on Earth. But by dating the appearance of tiny marine fossils that are known to have evolved immediately after mass extinction, Keller’s team now concludes that the most intense period of volcanic eruptions ended right when the mass extinctions began.

In contrast, the asteroid, which landed off Mexico’s Yucatan peninsula and formed what’s called the Chicxulub crater, predated the mass extinction by some 300,000 years. Keller and like-minded geoscientists who have been poking holes in the asteroid theory for years now reached that conclusion in 2004, in a paper in the Proceedings of the National Academy of Sciences. The Chicxulub impact, they calculated from cores taken from the crater, simply came too early to the crime scene: the mass extinction did not get underway for millenia. There's never been a convincing explanation for why it would have taken so long for the dying to start. If the victim wasn't killed until long after the suspect left the scene, it's time to start looking for a new suspect.

The Indian volcanoes, on the other hand, were timed just right to poison the planet and wipe out much of its life. They spewed out sulfur dioxide that poisoned rivers, lakes and seas; chlorine gas that shredded the ozone layer and allowed dangerous ultraviolet radiation to reach Earth’s surface; and carbon dioxide that triggered a global-warming greenhouse effect.

Many other scientists (not to mention tourist guides and popular books) are sticking with the killer-asteroid theory, but it never hurts to be reminded that even the most popular theories in science are only as good as the next experiment.