A big body of scientific evidence backs the hypothesis that a major asteroid or comet impact was responsible for the mass extinction of many floral and faunal species, including the large dinosaurs, that marked the end of the Cretaceous period. Now, the theory that a volcanic eruption caused the death is gaining steam.
By Larry O'Hanlon
Some 20 years after its conviction in slaying of the dinosaurs, the Chicxulub impact crater is facing a retrial by a growing number of geologists who think the mass extinction event 65 million years ago was caused by something much larger. Not a larger meteorite, but a far bigger disturbance that was happening on the other side of the planet before, during, and after the Chicxulub impact: the massive Deccan Traps volcanic eruption.
The latest debate over the ultimate reason for the mass extinction is occurring this week at the Natural History Museum in London. Researchers from around the world are meeting there for the International Conference of Volcanism, Impacts and Mass Extinctions -- which includes a lot of new science on the extinction event that wiped out the dinosaurs. This is despite the fact that advocates for the Chicxulub theory published a paper three years ago, with a whopping 41 authors, reviewing the evidence and concluding once and for all that Chicxulub was the dino killer.
“That paper helped the volcanism side because it dismissed volcanism,” said Princeton University paleontologist Gerta Keller, who has long been skeptical of the timing of the Chicxulub impact and has sought answers to the Cretaceous-Tertiary (a.k.a., K-T, or Cretaceous-Paleogene) extinction in India's Deccan Traps, which are arguably the largest volcanic deposit on the planet.
While the timing has long been debatable, more recently, however, radiometric dating of the impact debris suggests the K-T event and the Chicxulub collision happened no more than 33,000 years apart.
Still, Keller's work, and that of others, has unearthed evidence that the Deccan Traps' series of eruptions were not only timed right, but they released an order of magnitude more climate altering greenhouses gases into the atmosphere than the single Chicxulub impact could have. What's more, they have been directly tied to extinctions in the oceans in that part of the world.
The research has revealed that the Deccan Traps had three main periods of eruption spanning some 2.5 million years. Each phase of eruption lasted on the order of 100,000 years or less and had within them powerful pulses that released roughly 10,000 cubic kilometers (2,400 cubic miles) of lava in less than a century and maybe even in just a decade, explained Vincent Courtillot of the University of Paris, who is among those presenting at the meeting.
That's enough lava, just from a single pulse of a larger eruption, to bury the state of Delaware under a mile of rock. And like all eruptions, the Deccan Traps released vast amounts of carbon dioxide and other greenhouse gases that would have rapidly altered Earth's climate.
“An impact alone is not likely to cause a mass extinction," Courtillot told DNews. "But in the K-T case an impact occurred after volcanism had started and added a major blow to the sequence of events.”