Jury still out on dinosaur whodunnit

Scientists can't settle on what killed off the dinosaurs about 66 million years ago.

Asteroid impact and volcanic armageddon still prime suspects, writes Rachel Feltman

It's one of the biggest unsolved whodunits in history: What killed off the dinosaurs? Scientists are pretty sure something awfully big slammed into the planet about 66 million years ago, but many suggest rampant volcanic activity may also have played a major role.

New research attempts to throw cold water on the volcanism theory. The new study, published on Tuesday in Nature Geoscience, uses modelling to show that the climate change caused by continental flood basalts - the massive, long-lasting volcanic eruptions occurring around the same time as the great asteroid impact - would have been relatively minor.

"I felt that a lot of people, when they tried to make statements about how much volcanism contributed - it was all very qualitative," lead researcher Anja Schmidt of the University of Leeds said. "So I wanted to put some numbers to it."

Schmidt and her colleagues gathered data from previous studies to estimate the sulphur dioxide that would be emitted by these eruptions, which lasted for years and could spout 150 Olympic-size swimming pools of lava per minute.

"In contrast to previous studies, some of which suggested that really drastic cooling would occur because of these emissions, maybe even enough to kill all plants and animals, we find that perhaps the situation wasn't that grim," Schmidt said. "We see some cooling, but I suggest that most plants and animals would have been fine in most parts of the world."

This isn't to say that a decade-long volcanic eruption wouldn't have caused a little planetary disruption: Schmidt's model showed that global temperatures would drop by about 4.5C, which is the difference between our average temperature now and during the last ice age.

But according to the same model, the change would abate after just 50 years. For the cooling to last long enough and be severe enough to cause a mass extinction, Schmidt said, the eruptions would have to last for a century or more - much longer than ever estimated.

Princeton University's Gerta Keller, who also studies the role of volcanism in the demise of the dinosaurs, called the new study an "excellent effort" but was sceptical of its conclusions. We don't know enough about when these eruptions occurred and how long they lasted to draw conclusions from such models, she explained.

"I'm afraid that until we have more precise age data for all major lava flows preceding the mass extinction and the periods of non-activity in between lava flows, no model, however well conceived, can realistically evaluate the biotic and environmental effects of the large continental flood basalt provinces," Keller said.

"I bet that in a few years when this data becomes available, the same model based on high-precision age dating of lava flows will yield significantly different conclusions."

Schmidt said a better understanding of the tempo of the eruptions is the next step. She also pointed out that her study focused on only sulphur dioxide, that is known to have major climate impacts. It's possible other, less harmful gases emitted by continental flood basalts would have a cumulative effect on the climate and contribute to a mass extinction.

Some researchers have suggested the famous asteroid impact may have actually accelerated volcanic activity, another avenue to investigate.

As the Earth edges toward another mass extinction - this one almost certainly caused by the emissions of human industry - Schmidt believes it's important to pin down a culprit for the death of the dinosaurs.

"A group of really powerful and intriguing species went extinct, and it's important to understand because it happened very fast, and we don't have a universal agreement about how," Schmidt said. "We really have no idea."