Report bolsters view that asteroid killed most dinosaurs

An asteroid, not volcanoes, is to blame for the mass extermination of non-avian dinosaurs more than 60 million years ago, according to a recent study.

That’s the assessment of a study performed by researchers from Imperial College London, the University of Bristol and University College London. It offers support to a theory originated by American physicist Luis Álvarez four decades ago.

The new work from Alfio Alessandro Chiarenza, Alexander Farnsworth, Philip D. Mannion, Daniel J. Lunt, Paul J. Valdes, Joanna V. Morgan and Peter A. Alli indicates the Chicxulub asteroid caused a lengthy winter on the planet that killed the majority of living creatures on Earth.

Álvarez, working with his son geologist Walter Álvarez and nuclear chemists Frank Asaro and Helen Michel, proposed the reason for the Cretaceous-Paleogene extinction was the impact from the massive asteroid that struck at Chicxulub, Mexico, 66 million years ago.

While at first assailed by geologists, it has become the accepted reason for the mass extermination of most dinosaurs, except for those that adapted and became birds. However, some scientists argued that the formation of the Deccan Traps in west-central India, among the largest volcanic features on the planet, was responsible. 

Chiarenza and other researchers showed, by using modeling tools that examined climate and ecological evidence, that the Deccan Traps were not to blame for the mass extermination. Instead, the huge asteroid’s impact threw so much dust, sulfur and other material into the air that sunlight was blocked, creating a lengthy winter-like state that proved fatal to most dinosaurs.

“As a general summary, I can say that we combined for the first time climate and ecological modeling tools, to test quantitatively the effects of environmental agents on dinosaur habitats at the end of the Cretaceous,” Chiarenza told Current Science Daily. “By doing so we demonstrated that an impact winter scenario triggered by the Chicxulub asteroid has substantial detrimental effect on dinosaur habitats. On the other hand, we were not able to obtain such an extinction state by modelling the effects on climate of Deccan volcanism, the other main competing hypothesis to explain the end-Cretaceous extinction.

“In addition we show that the effect of concomitant eruptions of the Deccan traps might have acted as an ameliorating agent on the climate after the asteroid hit, buffering the negative effects on environment and global ecosystems that the asteroid impact produced at the Cretaceous–Paleogene boundary.”

Chiarenza said the study showed that the volcanic activity would have had the exact opposite effect on the Earth as the asteroid.

“I think that the most fascinating aspect of this study is the partial frame shift that we are seeing on considering the Deccan volcanism from a potential driver of extinction to be re-evaluated as an agent of recovery,” he said.

“Usually the reaction I get from people is that they want to know what killed the dinosaurs and that they ‘heard it was the asteroid, or climate change, or the volcanoes,'" Chiarenza said. “It is interesting to expose them to what science tells us and how that might be a more complex but somewhat interesting story made of an intricate interplay of different agents. Whereas the asteroid might have been the sole killer for the dinosaurs and the rest of the end Mesozoic fauna, volcanism might have avoided an even worse extinction than what happened.”

He said the debate is not over.

“There is still a minority of Earth scientists advocating for Deccan to be either a contributor or the main driver of the K/Pg extinction,” Chiarenza said. “The majority of geologists and paleontologists support the other view, and based on many other evidence than those presented or discussed in our paper. I hope this kind of approach may boost the interest in different analytical methods to investigate mass extinction and recovery in general, not only related to the K/Pg.”

The new report is highlighted by images and graphics that help explain the conclusion. 

“As for my favorite figure, maybe Figure 4 as it's a simple histogram that shows the amount of habitat available for non-avian dinosaurs at different extinction scenarios,” Chiarenza said. “That's the innovative aspect of this project. It puts numbers for the first time in the modelization of a mass extinction.”