For years, scientists have floated an alternative theory to explain the extinction of the dinosaurs—one involving extreme volcanism. It’s an intriguing idea, but new research seems to have finally put this competing explanation to rest.
Sixty-six million years ago, all dinosaurs (except for birds) were wiped from the face of the Earth. Did the final blow come from devastating volcanic eruptions, or a catastrophic asteroid impact?
To answer this decades-old question, researchers led by The University of Manchester reconstructed the average air temperatures of the 100,000 years preceding the extinction event. Their findings, detailed in a December 18 study published in the journal Science Advances, confirm that the infamous asteroid was indeed responsible for the end-Cretaceous mass extinction.
Also known as the K–T extinction, this era—marked by immensely violent geological and astronomical events—witnessed the end of about 80% of all species. What’s indisputable about this pivotal moment in Earth’s history is that a 6.2 to 9.3-mile-wide (10 to 15-kilometer) asteroid struck what is now modern-day Mexico. Around the same time, however, volcanoes in what is now India experienced some of the largest eruptions in Earth’s history.
To study the timing and intensity of these disasters, the team—including scientists from the University of Plymouth, Utrecht University, and Denver Museum of Nature and Science—analyzed prehistoric layers of partially decayed organic matter, called peat, from Colorado and North Dakota. The peat samples they studied contained unique molecules produced by bacteria whose structure changes based on the temperature. By inspecting these molecules, they were able to reconstruct a timeline for the average annual air temperature of the 100,000 years before the extinction.
The researchers found that volcanic carbon dioxide emissions gradually warmed the planet by 5.4 degrees Fahrenheit (3 degrees Celsius) during that period. They also noted a brief cooling by about 9 degrees Fahrenheit (5 degrees Celsius) likely caused by a major volcanic eruption that blocked out the sunlight with its sulfur emissions around 30,000 years before the mass extinction.
The cold snap was (relatively) brief, however, because the temperatures returned to their previous levels about 10,000 years later. As a consequence, the researchers suggest that the impact volcanic eruptions had on the climate were insufficient to wipe out the dinosaurs.
“The sulphur would have had drastic consequences for life on earth. But these events happened millennia before the extinction of the dinosaurs, and probably played only a small part in the extinction of dinosaurs,” Lauren O’Connor of Utrecht University, who led the study, said in The University of Manchester statement.
“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,” said Rhodri Jerrett of The University of Manchester, who contributed to the study.
The two peat samples yielded a similar temperature timeline. Because their original locations are about 466 miles (750 kilometers) apart, the researchers are confident that their results represent global temperature patterns rather than local. Additionally, their results also “match other temperature records from the same time period,” they wrote.
“This research helps us to understand how our planet responds to major disruptions,” added Bart van Dongen of The University of Manchester, who worked on the research. “The study provides vital insights not only into the past but could also help us find ways for how we might prepare for future climate changes or natural disasters.”
In the end, it’s clear the asteroid packed the bigger punch, wiping out the dinosaurs while volcanoes barely moved the needle. Studying these ancient events might not change the past, but it could help us make sense of how our planet reacts to catastrophe.