Did Volcanoes Kill the Dinosaurs?

Weighing the Evidence for and Against Volcanic Dinosaur Extinction Theories

Did a volcano like this one kill the dinosaurs? (Wikimedia Commons).

Sixty-five million years ago, give or take a few hundred thousand years, a meteor smashed into Mexico's Yucatan Peninsula, throwing up billowing clouds of ash and smoke that quickly spread, over the next few days and weeks, across the world's atmosphere. Blotted out, the sun could no longer nourish the earth's teeming ferns, forests and flowers, and as these plants died, so did the animals that fed on them--first the herbivorous dinosaurs, and then the carnivorous dinosaurs whose populations these plant-eaters sustained.

(See also 10 Myths About Dinosaur Extinction and The Earth's 10 Biggest Mass Extinctions.)

That, in a nutshell (or a meteor crater), is the story of the K/T Extinction Event. But some experts think this story is incomplete: it has a suitably thrilling climax, to be sure, but not enough attention has been paid to the events leading up to it. Specifically, evidence exists that the five million years leading up to the K/T Extinction witnessed a huge surge in volcanic activity--and that lung-choking, sun-blocking volcanic ash, every bit as much as meteor debris, may have weakened dinosaurs to such an extent that they were easy pickings for the Yucatan disaster.

The Volcanoes of the Late Cretaceous Period

Throughout its history, the earth has been geologically active--and during the late Cretaceous period, 70 million years ago, the most geologically active place on earth was northern India, near modern-day Mumbai.

(This had nothing to do with the slow collision of India with the underside of Eurasia, which wouldn't occur for another ten million years, but stresses in the fast-moving subcontinental plate were certainly involved.) Specifically, the volcanoes of the "Deccan Traps" spewed lava for tens of thousands of years on end; this lava eventually covered over 200,000 square miles of the subcontinent and reached a depth (in some locations) of over a mile!

As you can imagine, the Deccan Traps were bad news for local Indian and Asian wildlife, as terrestrial and marine animals were literally cooked alive and then buried beneath millions of tons of solidifying lava. But the traps may also have had a disastrous effect on the worldwide ecology, since volcanoes are notorious for releasing high levels of sulfur and carbon dioxide--which would have both acidified the world's oceans and caused a rapid spate of global warming, even despite all the accompanying dust thrown up into atmosphere. (Carbon dioxide is a greenhouse gas, meaning it tends reflects heat from the earth back onto the surface, rather than allowing it to dissipate into outer space.)

Volcano Extinction vs. Meteor Extinction - Which Theory Is Right?

What makes the volcano scenario hard to prove or disprove, vis-a-vis the meteor impact theory of dinosaur extinction, is that it depends on much of the same evidence. One key piece of data adduced by supporters of the Yucatan meteor impact is the characteristic layer of iridium, an element common in asteroids, in sediments laid down at the Cretaceous/Tertiary boundary. Unfortunately, iridium is also found in the molten rock under the earth's crust, which can be expelled by volcanoes!

The same applies to shocked-quartz crystals, which can be caused by either meteor impacts or (at least according to some theories) intense volcanic eruptions.

What about the dinosaurs themselves, and their persistence--or lack of it--in the fossil record? We know that dinosaurs roamed the earth right up until the K/T boundary, 65 million years ago, whereas the Deccan Traps became active 70 million years ago. That's a very "soft" boundary extinction of five million years, while it's clear that dinosaurs went extinct within a couple of hundred thousand years of the Yucatan meteor impact--a relatively "hard" boundary extinction by geological standards. (On the other hand, there is some evidence that dinosaurs were dwindling in diversity during the last few million years of the Cretaceous period, which may or may not be attributable to volcanic activity.)

In the end, these two scenarios--death by volcano and death by meteor--are not inconsistent with one another. It may very well be the case that all terrestrial life on earth, including dinosaurs, was profoundly weakened by the Deccan Traps, and the Yucatan meteor delivered the proverbial coup de grace. In effect, a slow, painful extinction was followed by a fast, even more painful extinction (which brings to mind that old saying about how people go bankrupt: "a little bit at a time, and then all at once.")

Volcanoes May Not Have Killed the Dinosaurs - But They Made Dinosaurs Possible

Ironically, we do know one instance in which volcanoes had a major impact on dinosaurs--but it happened at the end of the Triassic period, not the Cretaceous. A new study makes the solid case that the end-Triassic extinction event, which doomed more than half of all terrestrial animals, was caused by volcanic eruptions accompanying the breakup of the supercontinent Pangaea. It was only after the dust had cleared that the earliest dinosaurs--which evolved during the middle Triassic period--were free to fill the open ecological niches left by their doomed relatives, and assert their dominance during the ensuing Jurassic and Cretaceous periods.