“This cooling changed the climate so much that it made it difficult for the dinosaurs, and the meteorite was the coup de grâce,” said Don Baker, study co-author and geochemist at McGill University. “That was the final extinction event, but they were not in good shape before the time of that meteorite impact.”
Earth’s temperature was dropping long before the meteorite hit, according to some research. But scientists hadn’t pinpointed a cause, so Baker and his team looked to a volcanic explanation.
A meteorite is a popular theory for the demise of the dinosaurs (birds aside), but volcanic eruptions are another contested explanation. The evidence lies in one of the largest volcanic provinces in the world, known as the Deccan Traps. Located in present-day west-central India, the area had massive outpourings of lava around the time the dinosaurs went extinct.
If you visit the site today, the lava from past eruptions can be seen stacked on each other in layers. In some parts, the layers are more than a mile thick and cover nearly 200,000 square miles (around the size of Oregon and Washington state combined).
Any eruption of that size would have drastically changed the environment, expelling gasses — like sulfur dioxide — that would have reflected sunlight back into space and caused cooling at Earth’s surface on large scales.
“The eruptions were continuous, one on top of another, for hundreds of thousands of years according to our dating,” said Paul Renne, co-author and geochronologist at University of California at Berkeley, in an email. “This level of volcanic activity, covering hundreds of thousands of square miles, is rare in geologic history.”
To investigate the gases emitted during these ancient lava flows, the team hammered out rocks in the Deccan Traps. Elements are largely lost to the atmosphere during an eruption, but a small portion are trapped in minerals as the lava cools at the end of an eruption.
The team developed a new technique to measure the amount of sulfur and fluorine in the minerals. They also recreated conditions in a lab to determine how much sulfur or fluorine would be needed in the environment to get that amount in the crystal.
Right before the supposed dinosaur-killing meteorite hit Earth, the team found the lava flows had decent concentrations of fluorine that could have had local effects, such as acid rain, plant failure or animal poisoning. But sulfur concentrations in the lava flows were extremely high — enough to trigger a major drop in temperature around the world.
The volcanic eruptions would have been unlike anything we would have experienced in human history. A relatable, but very inadequate, comparison would be the powerful eruption from Mount Pinatubo in 1991. It ejected on the order of ten cubic kilometers of magma and caused global temperatures to drop by around half a degree over a year.
By comparison, some of these ancient eruptions ejected up to a hundred cubic kilometers, Baker said. The temperature drop would be much more dramatic and persistent, with a seemingly perpetual winter (cue Game of Thrones music). He points to some research that suggests the drop could have even been 10 degrees Celsius cooler over a decade.
“If you have these big eruptions, every ten years, the temperature drops and it stays cold,” said Baker. “Once you change the temperature, it’s global change, which is far more than temperature … that includes changing the wind patterns, rain patterns, everything else.”
The dinosaurs probably didn’t have time to adapt, if that was the case. The first temperature drop probably occurred in the span of less than a decade, with each year getting a little colder than it was before, Baker said.
It’s hard to decisively know what was happening with the dinosaurs during that time, but scientists are constantly trying to solve that puzzle. In the end, there likely isn’t a simple, or maybe even a single, explanation for why the dinosaurs went extinct, Baker said. But let the dinosaurs serve as an example of what happens when Earth changes too fast — a cautionary story for climate change today.
“Rapid climate change, no matter how it happens, can be very dangerous for species on Earth,” Baker said. “Any sort of rapid change faster than evolution can adapt or migration can adapt to is going to be problematic.”
