Massive volcanic eruptions did not cause the extinction of dinosaurs, say climate scientists

Massive volcanic eruptions on the Indian peninsula have long been proposed as an alternative cause for the demise of the dinosaurs. This phase of active volcanism took place in a period just before Earth was struck by a meteorite, 66 million years ago. The effect of these volcanic eruptions on Earth’s climate has been the topic of fierce scientific debate for decades.

Now, climate scientists from Utrecht University and the University of Manchester show that while the volcanism caused a temporary cold period, the effects had already worn off thousands of years before the meteorite impacted. The scientists therefore conclude that the meteorite impact was the ultimate cause of the dinosaur extinction event.

The study is published in the journal Science Advances.

The meteorite impact in the Gulf of Mexico roughly 66 million years ago is well researched and widely known as the defining end of the dinosaur age. But Earth scientists have fiercely debated for decades whether a massive outpouring of lava on the Indian continent, which occurred both prior to and after the meteorite impact, also contributed to the demise of dinosaur populations roaming Earth.

These volcanic eruptions released vast amounts of CO₂, dust, and sulfur, thereby significantly altering the climate on Earth—but in different ways and on different timescales to a meteorite impact.

Ancient peats

The new publication provides compelling evidence that while the volcanic eruptions in India had a clear impact on global climate, they likely had little to no effect on the mass extinction of the dinosaurs.

By analyzing fossil molecules in ancient peats from the United States of America, the scientific team reconstructed air temperatures for the time period covering both the volcanic eruptions and the meteorite impact. Using this method, the researchers show that a major volcanic eruption occurred about 30,000 years before the meteor impact, coinciding with at least a 5° Celsius cooling of the climate. They also conclude that this cooling was likely the result of volcanic sulfur emissions blocking sunlight from reaching Earth’s surface.

Importantly, the scientists discovered that by around 20,.000 years before the meteorite impact, temperatures on Earth had already stabilized and had climbed back to similar temperatures before the volcanic eruptions started. This period of global warming was likely aided by volcanic CO₂ emissions, says Lauren O’Connor at Utrecht University.

“These volcanic eruptions and associated CO₂ and sulfur release would have had drastic consequences for life on Earth. But these events happened millennia before the meteorite impact and probably played only a small part in the extinction of dinosaurs,” she explains.

Impact winter

With the effects of volcanism practically ruled out, this would leave the Chicxulub meteorite impact as the primary cause of the dinosaur mass extinction.

“By comparison, the impact from the asteroid unleashed a chain of disasters, including wildfires, earthquakes, tsunamis, and an ‘impact winter’ that blocked sunlight and devastated ecosystems. We believe the asteroid that ultimately delivered the fatal blow,” says Rhodri Jerrett at the University of Manchester.

The fossil peats that the researchers analyzed contain specific membrane-spanning molecules produced by bacteria. The structure of these molecules changes depending on the temperature of their environment. By analyzing the composition of these molecules preserved in ancient sediments, scientists are able to calculate past temperatures.

O’Connor adds, “This way, we were able to create a detailed ‘temperature timeline’ for the years leading up to the dinosaur extinction, which we can compare to the fossil record to understand the relative timing of events.”

Researchers from Utrecht University, the University of Manchester, Plymouth University, and the Denver Museum of Nature and Science are now applying the same approach to reconstruct past climates at other critical periods in Earth’s history.