The theory that volcanic eruptions had a finger in the pie can be dismissed.

The world changed completely about 66 million years ago. Not only did the dinosaurs disappear, 75 percent of all life on Earth went extinct. Scientists have long debated the cause. Was this catastrophic event the result of an asteroid colliding with Earth, or was it due to massive volcanic eruptions that had plagued our planet for tens of thousands of years?

Cause
In a new study, researchers investigated the real cause of the dinosaur extinction. To determine whether asteroid or volcanism was the culprit, the researchers used powerful mathematical models. They combined this with information about what environmental factors – such as rainfall and temperature – each dinosaur species needed to thrive. The team then mapped out where these conditions still existed in a world after a disastrous asteroid impact or massive volcanic eruptions. “We added an ecological dimension to the study, as it were, to reveal how climatic fluctuations have seriously damaged dinosaur ecosystems,” explains researcher Alex Farnsworth.

Asteroid
The researchers found that asteroid impact destroyed all habitats of dinosaurs, while volcanism left some habitable areas around the equator. It means that only a planetoid impact created fatal conditions that were very unfavorable to dinosaurs. “The asteroid produced decades of winter,” explains Alessandro Chiarenza. This winter was characterized by cold and darkness, caused by dust and aerosols blown into the atmosphere by the impact, blocking the sunlight. As a result, temperatures were well below freezing point for most of the year in most places on Earth. “The effects of massive volcanic eruptions, on the other hand, were not strong enough to significantly disrupt global ecosystems.”

Even this armored Ankylosaurus was no match for the disastrous asteroid impact. Image: Fabio Manucci

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It is true that volcanic eruptions also produce particles and gases that block sunlight. In contemporary India, at the time of mass extinction, massive volcanic eruptions took place, with some 500,000 cubic kilometers of lava making its way across the Earth’s surface to form the well-known Deccan Traps volcanic plain. In the short term, these eruptions would indeed have blocked sunlight, leading to a veritable ‘volcanic winter’. However, volcanoes also release carbon dioxide, a greenhouse gas. And although in the long term the blackout particles will whirl down again, carbon dioxide actually builds up in the atmosphere. This would have caused the planet to warm up again.

New life
It means that these volcanic eruptions actually contributed to the emergence of new life. After an initial drastic global winter caused by the asteroid impact, the researchers’ model suggests that volcanic warming has helped restore many habitats. And this gave life a new chance. So instead of volcanic eruptions ushering in the end of the dino era, they actually helped rebuild life. “The warming caused by volcanism has helped the animals and plants that survived the asteroid impact,” says Chiarenza. “Many groups – including birds and mammals – therefore increased in numbers in the immediate aftermath.”

How did new life arise?
One’s dead is the other’s bread. With the disappearance of the dinosaurs and large marine reptiles, space was created for the evolution of other species: mammals and ultimately humans. How that life could turn out afterwards? In fact, the crater was colonized by surviving species. For example, life in the Chicxulub crater returned within a few months to years. Then, about 30,000 years after impact, the crater consisted of a new, thriving ecosystem. Phytoplankton supported a diverse community of organisms in surface water and on the sea bed. Evolution then led to the emergence of a large number of new species.

The findings indicate that the sole culprit for the dinosaurs’ extinction was the ten-kilometer asteroid that created a 200-kilometer-wide crater in modern-day Mexico. This fatal asteroid could not have taken a worse course. The asteroid headed for its target at a steep angle of up to sixty degrees. And that was the worst case scenario for the dinosaurs.