Most dinosaurs were killed by climate change, not a meteorite, new study suggests

Perhaps the most famous thing about the dinosaurs is the giant space rock that seemingly killed them. Also known as the Chicxulub impact, or the K-Pg event, most people are familiar with the major crash roughly 66 million years ago after a comet or asteroid collided with our planet.

It was one of the most violent upheavals in Earth's entire 4 billion year history. The collision was so massive, it killed approximately 60 percent of life in the oceans and wiped out the non-avian dinosaurs, as well as killing most four-legged animals over 25 kilograms (55 pounds). Though it was massively destructive, in the process, the K-Pg event cleared the way for modern life forms to evolve, including us humans.

At least, that is the story most of us have been taught for generations. Yet the truth may actually be more complex. According to a recent study in the journal Science Advances, climate change might have also played a major role in the extinction of the dinosaurs.

The scientists behind that paper determined this by studying the Deccan Traps of western India, which were formed by molten lava after a massive volcanic eruptions 66 million years ago. They wanted to learn how much fluorine and sulfur were burped into the atmosphere as volcanoes spewed one million cubic meters of rock.

After developing a new scientific technique for analyzing this, the researchers determined that the amount of fluorine ejected by these eruptions varied from 400 to 3000 parts per million, enough to radically alter the regional environment but not the entire planet. The same cannot be said of the emitted sulfur, which reached up to 1800 parts per million — and, notably, occurred shortly before the K-Pg event (within 0.1 million years).

"Our data suggest that volcanic sulfur degassing from such activity could have caused repeated short-lived global drops in temperature, stressing the ecosystems long before the bolide impact delivered its final blow at the end of the Cretaceous," the authors write.

If subsequent research reinforces this conclusion, it could rock the foundations of how humans understand Earth's ancient history. Instead of imagining the K-Pg extinction as being singularly caused by a giant object colliding with our planet, the new findings paint a different picture: One in which volcanoes erupted and caused major climate fluctuations, which were then compounded by the devastating impact of the asteroid or comet.

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“Our research demonstrates that climatic conditions were almost certainly unstable, with repeated volcanic winters that could have lasted decades, prior to the extinction of the dinosaurs," McGill University Professor Don Baker, who co-authored the paper, said in a statement. "This instability would have made life difficult for all plants and animals and set the stage for the dinosaur extinction event. Thus our work helps explain this significant extinction event that led to the rise of mammals and the evolution of our species."

As it turns out, scientists have long been aware of the role that volcanoes play in changing our climate. Some scientists hypothesize that the so-called Little Ice Age — a period of pronounced cooling that occurring during the Medieval era — occurred as a result of a cluster of large volcanic eruptions that occurred in close succession. This type of climate change is natural, in sharp contrast to the anthropogenic climate change we are causing by burning fossil fuels.

"At our human timescale (a few years to a few hundred thousand years), most volcanic eruptions have a net cooling effect on the climate," Dr. Yves Moussallam, Assistant Professor of Earth and Environmental Sciences and Geochemistry at Columbia Climate School, told Salon by email earlier this year. Moussallam cited global cooling periods that occurred after the eruption of Tambora in 1815 and Mt. Pinatubo in 1991. "This is because of another gas which is emitted by volcanoes, sulfur dioxide. In the atmosphere SO2 turns to H2SO4 (sulfuric acid) which condenses into little droplets (aerosols). If these are injected into the stratosphere, they can remain there for several months to years and have a net cooling effect on the surface as they reflect part of the Sun's radiation."

In his recent book "Our Fragile Moment," University of Pennsylvania professor of earth and environmental science Dr. Michael E. Mann detailed how the history of life on Earth is inextricably tied to the alterations that occur in its climate. This includes, but is hardly limited to, volcanic eruptions.

"Life on Earth has been around for 4 billion years, and so for billions of years, conditions have been conducive to life and life has played an increasingly important role on the climate itself," Mann told Salon earlier this year. This includes Snowball Earth, or a theoretical period when Earth's surface was mostly or entirely frozen, as well as mass extinction events that altered the climate from 250 million years ago and the K-Pg event. "Then we zoom ahead to just a few million years ago, and primates are on the scene. At every step, you have climate changing and climate impacting life," Mann pointed out.

At the same time, it is important to note that even though volcanic eruptions may have contributed to climate change when dinosaurs roamed the Earth, that does not mean that volcanic activity is responsible for modern climate change. The science simply does not bear that out claim, which is made by many climate change deniers.

"The burning of fossil fuels and the manufacture of cement releases 37 Gt (billion tones) of CO2 into the atmosphere per year," Moussallam explained. "Volcanoes are estimated to supply globally 0.28–0.36 Gt CO2 per year to the atmosphere and ocean system." By contrast, "Volcanoes hence contribute about 100 times less CO2 than anthropogenic activities."