Climate change killed the dinosaurs, but what caused it? A massive asteroid strike or thousands of years of volcanic eruptions?
Sixty-six million years ago an asteroid or comet smashed into Earth off the coast of Mexico just as tens of thousands of volcanoes were busy spewing ash and gas into Earth’s atmosphere.
Dinosaur extinction: asteroid or volcanoes?
Did the Chicxulub asteroid impact and its aftermath kill-off the dinosaurs? Or was it the volcanoes’ effect on turning Earth’s atmosphere toxic? For the first time scientists have shown that the asteroid impact’s after-effect was a “permanent winter” that the dinosaurs simply couldn’t survive.
“We show that the asteroid caused an impact winter for decades, and that these environmental effects decimated suitable environments for dinosaurs,” said lead researcher Dr. Alessandro Chiarenza at Imperial College London.
The new study was published today in Proceedings of the National Academy of Sciences.
What is the Cretaceous-Paleogene extinction event?
It’s the sudden mass extinction of three-quarters of the plant and animal species on Earth, approximately 66 million years ago. The only dinosaurs that survived were the ancestors of what are now birds.
Scientists aren’t certain whether it was caused by the Chicxulub asteroid impact or by a long period of volcanic eruptions around the same time. Around the time of the mass extinction—and the asteroid strike—there were tens of thousands of eruptions at the Deccan Traps in what is now India.
“The effects of the intense volcanic eruptions were not strong enough to substantially disrupt global ecosystems,” said Chiarenza. “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.”
The new study doesn’t just suggest that the asteroid created a world that dinosaurs couldn’t have survived in.
It also suggests that those volcanic eruptions may have actually been instrumental in allowing some life on Earth to survive.
The Chicxulub asteroid impact “extinction event” appears to have killed-off almost 75% of life on Earth. As the asteroid struck it would have released particles and gases high into the atmosphere, say the researchers, blocking out the Sun for years.
So would volcanoes, argue the researchers, but they also emit carbon dioxide, a greenhouse gas. That could have been been decisive for some species.
While the asteroid strike wiped out all dinosaur habitats in an immediate “drastic global winter,” the effects would have waned in the long-term.
Not so the build-up of carbon dioxide, which would have warmed-up the planet and so helped restore some habitats near Earth’s equator, thus making them viable for mammals and birds to continue to exist.
The volcanic eruptions, say the researchers, “buffered” the negative impacts of the asteroid impact on Earth’s climate.
“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,” said Chiarenza.
“This volcanic-induced warming helped boost the survival and recovery of the animals and plants that made it through the extinction, with many groups expanding in its immediate aftermath, including birds and mammals.”
‘Blue screen of death’ for dinosaurs
The research team from Imperial College London, the University of Bristol and University College London combined geological markers of climate, powerful mathematical models, and the climate features—such as rainfall and temperature—that each species of dinosaur needed to thrive. They then mapped where these conditions would still exist in a world after either an asteroid strike or massive volcanism.
“In this study we add a modelling approach to key geological and climate data that shows the devastating effect of the asteroid impact on global habitats,” said co-author Dr Philip Mannion, from University College London. “It produces a blue screen of death for dinosaurs.”