Everyone knows that the asteroid that crashed into Earth 65.5 million years ago caused or at least accelerated the extinction of non-avian dinosaurs, but also caused mass extinctions in the oceans. Interestingly, however, the extinction rate was significantly lower for organisms that resided in inland lakes and rivers.
Part of the scientific community now believes it can explain this gap: According to a study published in 2013, the biological adaptations that certain organisms developed to survive in a freshwater environment also protected them from months of freezing darkness after the asteroid impact.
“Freshwater organisms are resilient to physical and chemical fluctuations far beyond what marine organisms can withstand,” says William Lewis, co-author of the study and freshwater specialist at the University of Colorado.
Therefore, in freshwater environments, many organisms are adapted to freeze-thaw cycles and periods of oxygen deprivation. Most enter a dormant state, hibernating or burying their eggs in mud, behavior that could have allowed them to avoid the worst consequences of the impact.
“Quietness also exists in the marine environment,” explains Lewis, “but it is an unusual behavior because it is not necessary for most organisms.” »
These results, published online in the Journal of Geophysical Research – Biogeosciences, provide a level of specificity that the field desperately needed after a long time mired in generalities, experts lament.
“So far, I think efforts have focused on the collapse of the food chain to explain the extinction of certain groups,” says Alison Murray, a paleontologist at the University of Alberta in Canada who was not involved in the study.
“In this study, the authors expand on the theory of food chain collapse, but go into more detail by looking at different groups and determining which of them could survive without light for long periods of time, beyond which would be the loss of photosynthetic organisms. “Explains Murray via email.
David Fastovsky agrees on this point: “I had never seen a detailed account of our vision of how the mass extinction would unfold,” adds the paleontologist from the University of Rhode Island. “But here is a model in black and white of how it all could have happened. »
As the study’s lead author, Douglas Robertson, a geophysicist at the University of Colorado, has shown in previous work, the asteroid that crashed into what is now the Gulf of Mexico likely triggered a global firestorm, ejecting enormous amounts of vaporized rock from the atmosphere out.
When these ejecta fell back to Earth a few hours later, they would have entered the atmosphere at such a rate that the heat generated by their fall would have lit the sky with a red glow and ignited vegetation on the ground.
“The radiation and flames would have been fatal within hours to any life form that did not seek refuge underground or underwater,” says Robertson. “The dinosaurs all disappeared shortly after the impact. »