Artwork of a pair of tyrannosaur dinosaurs surveying a volcanic landscape.gettyAbout 66 million years ago, a meteorite hit Earth near what today is the Yucatn peninsula, causing widespread destruction and death. But almost simultaneously, intense volcanism covered a vast area of the Indian subcontinent with over 2 kilometers thick lava flows. Scientists have long debated if the impact or the volcanic supereruption was behind the extinction of 75 percent of all species living at the time, including non-avian dinosaurs, or a combination of both.Based on a new study, scientists from Utrecht University and the University of Manchester show that while the volcanism caused a temporary climate change, the effects had already worn off thousands of years before the meteorite impacted and most species survived this first cold snap. The scientists therefore conclude that the meteorite impact was the ultimate cause of the mass extinction event at the end of the Cretaceous period.A meteorite impact can result in a thick layer of dust and soot blocking the sun and cooling the surface. Volcanic eruptions release vast amounts of carbon-dioxide, dust, and sulfur, thereby significantly altering the chemistry of the atmosphere and changing Earth's climatebut in different ways and on different timescales to a meteorite impact.By analyzing fossil molecules in sediments deposited around 65 to 66 million years ago in the interior of the North American continent, the scientific team reconstructed air temperatures for the entire time period.The analyzed sediments contain specific molecules produced by bacteria. The structure of these molecules changes depending on the temperature of the environment the bacteria once lived in. By analyzing the composition of these molecules in the sediment layers deposited every year, the scientists were able to reconstruct a climate curve covering both the timing of the volcanic eruptions and the meteorite impact.MORE FOR YOUThe study show that a major volcanic pulse occurred about 30,000 years before the impact, coinciding with at least a 5 degrees cooling of the climate. They also conclude that this cooling was likely the result of volcanic sulfur emissions."These volcanic eruptions and associated carbon-dioxide 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," explains study author Lauren O'Connor, a geochemist at Utrecht University.The scientists also discovered that by around 20,000 years before the impact, temperatures on Earth had already stabilized and had climbed back to similar temperatures before the volcanic eruptions started. This fast recovery was likely aided by volcanic emissions acting like greenhouse gases rapidly warming the planet.Graph showing how Earth's mean annual air temperatures (MAAT) dropped during a phase of intense ... [+] volcanism in India but returned normal shortly after the eruption peak. The end-Cretaceous meteorite impact happened 30,000 years after this peak.O Connor et al. 2024/Science AdvancesWith the effects of volcanism practically ruled out, this would leave the Yucatn meteorite impact as the primary cause of the later 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," concludes Rhodri Jerrett, geologist at the University of Manchester.The study, "Terrestrial evidence for volcanogenic sulfate-driven cooling event ~30 ka before the CretaceousPaleogene mass extinction," was published in the journal Science Advances and can be found online here.Additional material and interviews provided by Utrecht University.