By Stephen Beech
Massive volcanic eruptions did not cause the extinction of dinosaurs, according to a new study.
Volcanoes on the Indian peninsula have long been proposed as an alternative cause for the demise of the giant reptiles.
That phase of active volcanism took place in a period just before the Earth was struck by a meteorite, 66 million years ago.
The effect of those volcanic eruptions on the Earth’s climate has been a topic of fierce scientific debate for decades.
Now, climate scientists from the University of Manchester and Utrecht University in the Netherlands have shown that, while the volcanism caused a temporary cold period, the effects had already worn off thousands of years before the meteorite impacted.
The research team concluded that the meteorite impact was the ultimate cause of the dinosaur extinction event.
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 scientists have fiercely debated for decades whether a massive outpouring of lava on the Indian continent, which occurred both before and after the meteorite impact, also contributed to the demise of dinosaur populations.
The volcanic eruptions released vast amounts of carbon dioxide, dust, and sulfur, significantly altering Earth’s climate – but in different ways and on different timescales to a meteorite impact.
The new study, published in the journal Science Advances, now 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, the scientific team reconstructed air temperatures for the time period covering both the volcanic eruptions and the meteorite impact.
Using that method, the team showed 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 concluded that the cooling was likely the result of volcanic sulfur emissions blocking sunlight from reaching the Earth’s surface.
The team 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.
Dr. Lauren O’Connor, of Utrecht University, says the period of global warming was likely aided by volcanic CO2 emissions.
She said: “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.”
With the effects of volcanism practically ruled out, Dr. Rhodri Jerrett says that would leave the Chicxulub meteorite impact as the primary cause of the dinosaur mass extinction.
Dr. Jerrett, of the University of Manchester, said: “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.”
The fossil peats that the researchers analyzed contain specific membrane-spanning molecules produced by bacteria.
The structure of the molecules changes depending on the temperature of their environment.
By analyzing the composition of the molecules preserved in ancient sediments, scientists are able to calculate past temperatures.
Dr., O’Connor added: “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.”.
