Massive volcanic eruptions in the Indian Peninsula have long been proposed as an alternative cause of the dinosaurs’ extinction.
This phase of intense volcanic activity took place in a period that immediately preceded the fall of a meteorite on Earth, 66 million years ago. The impact of these volcanic eruptions on Earth’s climate has been the subject of heated scientific debate for decades.
Now, climatologists from Utrecht University and the University of Manchester show that although volcanism caused a temporary period of climate cooling, its effects disappeared thousands of years before the meteorite fell. Therefore, scientists conclude that the impact of the meteorite was the main cause of the extinction of the dinosaurs.
The study was published in the journal Science Advances.
The meteorite impact in the Gulf of Mexico, about 66 million years ago, is well studied and widely recognized as the moment that marked the end of the age of the dinosaurs. But geologists have argued for decades over whether massive lava eruptions on the Indian subcontinent, which occurred before and after the meteorite impact, contributed to the extinction of the dinosaur species that once populated Earth.
These volcanic eruptions released enormous amounts of CO2, dust and sulphur, significantly altering the Earth’s climate, but in different ways and periods than the meteorite impact.
The new research provides compelling evidence that while volcanic eruptions in India clearly had an impact on global climate, they probably had almost no effect on the mass extinction of the dinosaurs.
By analyzing fossilized molecules from ancient peatlands in the United States, the research team reconstructed the air temperature of the period covering both the volcanic eruptions and the meteorite impact. Using this method, the researchers demonstrate that a major volcanic eruption occurred approximately 30,000 years before the meteorite impact, causing a cooling of the climate by at least 5° Celsius. They also conclude that this cooling was likely the result of volcanic sulfur emissions blocking sunlight.
Importantly, the researchers discovered that, approximately 20,000 years before the impact of the meteorite, the temperature on Earth had already stabilized, returning to values similar to those before the volcanic eruptions. This period of global warming was likely driven by volcanic CO2 emissions, explains Lauren O’Connor of Utrecht University.
“These volcanic eruptions and their associated emissions of CO2 and sulfur could have had catastrophic consequences for life on Earth. But these events occurred thousands of years before the meteorite impact and probably played only a minor role in the extinction of the dinosaurs,” she explains.
If we largely exclude the influence of volcanism, the impact of the Chicxulub meteorite remains the main cause of the mass extinction of the dinosaurs.
“By comparison, the asteroid’s impact triggered a chain of catastrophes, including wildfires, earthquakes, tsunamis and an ‘impact winter’ that blocked sunlight and destroyed ecosystems. We think the asteroid finally delivered the final blow,” says Rodri Jerrett of the University of Manchester.
The fossilized peats analyzed by the researchers contain specific membrane molecules produced by bacteria. The structure of these molecules changes depending on the temperature of the environment. By analyzing the composition of these molecules preserved in ancient sediments, scientists can calculate past temperatures.
“Thus, we were able to create a detailed ‘thermal ladder’ for the years leading up to the dinosaur extinction, which we can compare with fossils to understand the relative chronology of events,” adds O’Connor.
Researchers from Utrecht University, Manchester University, Plymouth University and the Denver Museum of Natural Sciences are now applying the same approach to reconstruct the climate of other critical periods in Earth’s history.
