Massive volcanic eruptions on the Indian subcontinent have long been proposed as a possible cause for the extinction of the dinosaurs. These eruptions occurred shortly before Earth was struck by a meteorite, 66 million years ago. For decades, scientists have debated the impact of these volcanic events on Earth’s climate.
Now, climate scientists from Utrecht University and the University of Manchester present new findings showing that although the volcanic activity triggered a temporary cooling period, its effects had already dissipated thousands of years before the meteorite impact. Consequently, the researchers conclude that the meteorite impact was the primary cause of the dinosaurs’ extinction.
The meteorite impact in the Gulf of Mexico, which occurred around 66 million years ago, is widely recognised as the key event marking the end of the dinosaur era. However, for years, Earth scientists have debated whether the intense volcanic activity in India, which occurred both before and after the meteorite strike, also played a role in the extinction of the dinosaurs.
These volcanic eruptions released large amounts of CO2, dust and sulfur, significantly altering Earth’s climate but in ways and over timescales different from those caused by the meteorite impact.
Ancient peats
The new research provides strong evidence that while the volcanic eruptions did have an impact on global climate, they likely had minimal effect on the mass extinction event.
By analyzing fossil molecules in ancient peats from the United States, the scientists were able to reconstruct the air temperatures during the time of the eruptions and the meteorite impact. Their findings show that a major volcanic eruption occurred about 30,000 years before the meteor impact, coinciding with a climate cooling of at least 5°C. This cooling was likely caused by volcanic sulfur emissions that blocked sunlight.
However, by around 20,000 years before the meteorite struck, Earth’s temperatures had stabilized and returned to pre-eruption levels. This warming was probably aided by CO2 emissions from the volcanoes, according to Lauren O’Connor from Utrecht University.
“While the volcanic eruptions and the associated release of CO2 and sulfur had severe effects on life on Earth, these events occurred millennia before the meteorite impact and likely played a small role in the extinction of the dinosaurs,” O’Connor explains.
Winter impact
With the volcanic effects now ruled out, the Chicxulub meteorite impact emerges as the main cause of the dinosaur extinction.
“The asteroid’s impact triggered a chain of catastrophic events, including wildfires, earthquakes, tsunamis, and an ‘impact winter’ that blocked sunlight and devastated ecosystems,” Rhodri Jerrett from the University of Manchester explained. “We believe the asteroid delivered the fatal blow”.
The researchers used fossil peats to analyze specific molecules produced by bacteria. These molecules change in structure based on environmental temperature. By studying these molecules preserved in ancient sediments, the scientists were able to reconstruct past temperatures.
“Through this method, we created a detailed ‘temperature timeline’ for the period leading up to the dinosaurs’ extinction, which we can now compare to the fossil record to understand the timing of events more clearly,” O’Connor added.
Scientists from Utrecht University, the University of Manchester, Plymouth University, and the Denver Museum of Nature and Science are now applying the same approach to study past climates at other crucial points in Earth’s history.