An asteroid impact, not volcanic activity, killed the dinosaurs, a new study finds.
For decades, scientists have gone back and forth over exactly what caused a mass extinction event 66 million years ago, which destroyed about 75% of all life on Earth, including all of the large dinosaurs. Some have thought that volcanic activity could be to blame, but one new study shows that a giant asteroid impact was the prime culprit.
Scientists have known that the impact, which created the massive Chicxulub impact crater (located in what is now the Yucatán Peninsula in southeast Mexico), was a major contributing factor to this extinction event. But volcanic activity happening at around the same time has raised questions over which could have been the main factor which changed conditions on our planet that led to the demise of Earth's creatures.
In a new study, researchers from Imperial College London, the University of Bristol and University College London have shown that the asteroid impact, not volcanic activity, was the main reason that about 75% of life on Earth perished at that time, and it did so by significantly interfering with Earth's climate and ecosystems.
"We show that the asteroid caused an impact winter for decades, and that these environmental effects decimated suitable environments for dinosaurs. In contrast, the effects of the intense volcanic eruptions were not strong enough to substantially disrupt global ecosystems," lead researcher Alessandro Chiarenza, who conducted this work whilst studying for his PhD in the Department of Earth Science and Engineering at Imperial, said in a statement. "Impact winter" signifies a semi-permanent "winter" created when sunlight-blocking particles are kicked up into the atmosphere after an impact. "Our study confirms, for the first time quantitatively, that the only plausible explanation for the extinction is the impact winter that eradicated dinosaur habitats worldwide."
To come to this conclusion, the researchers modeled how Earth's climate would be expected to respond to two separate possible extinction causes: volcanism and asteroid impact. In these mathematical models, they included environmental factors including rainfall and temperature, which would have been critical to the survival of these species. They also included the presence of sunlight-blocking gases and particles and carbon dioxide, a greenhouse gas.
"Instead of only using the geologic record to model the effect on climate that the asteroid or volcanism might have caused worldwide, we pushed this approach a step forward, adding an ecological dimension to the study to reveal how these climatic fluctuations severely affected ecosystems," co-lead author Alex Farnsworth, a climatologist at the University of Bristol, added in the same statement.
With these models, the team found that the giant asteroid hitting our planet would have released tremendous amounts of gas and particles into Earth's atmosphere, blocking out the sun for years on end. This effect would have created a sort of semi-permanent winter on Earth, making the planet unlivable for most of its inhabitants.
Now, while the team found the asteroid impact to be the major factor in making Earth unlivable for most animals, they also found that volcanic activity could have actually helped life to recover over time, a conclusion that scientists have drawn before.
They found that, while volcanoes do release sunlight-blocking gases and particles, which would have helped to block the sun in the short term, they also release large amounts of carbon dioxide which, because it's a greenhouse gas, would have built up in the atmosphere and warmed the planet.
So, as the researchers suggest in this work, while the devastating winter caused by the asteroid killed off most life on Earth, over time, the warming effect created from the volcanic greenhouse gases could have helped to restore life to habitats.
"We provide new evidence to suggest that the volcanic eruptions happening around the same time might have reduced the effects on the environment caused by the impact, particularly in quickening the rise of temperatures after the impact winter. This volcanic-induced warming helped boost the survival and recovery of the animals and plants that made through the extinction, with many groups expanding in its immediate aftermath, including birds and mammals," Chiarenza added.
This work was published June 29 in the journal Proceedings of the National Academy of Sciences.
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