The two speeds of the Great Extinction

4 or 5 great mass extinctions have occurred on our planet, and we know that the worst of these events was that of about 252 million years ago (at the end of the Permian), when massive volcanic eruptions caused a catastrophic climate change, triggered by the of carbon dioxide (CO2) and acidic dust and aerosols in the atmosphere. The vast majority of animal species went extinct and as the dust from the eruptions settled, the planet entered the early days of the Age of the Dinosaurs. Scientists are still developing the scenarios that explain how and which animals went extinct, and which ones survived and why. In a study published in PNAS, a group of scientists presents an uncommon scenario: for the researchers, while the extinctions of many species occurred rapidly in the oceans, life resisted longer on land and the great extinction occurred more slowly.
A researcher at the Karoo Basin site in South Africa is working to free a Lystrosaurus fossil. This animal belonged to the Synapsid class, which included the ancestors of mammals. Between the end of the Permian and the beginning of the Triassic it was the most widespread herbivore on the planet.

A researcher at the Karoo Basin site in South Africa is working to free a Lystrosaurus fossil. This animal belonged to the Synapsid class, which included the ancestors of mammals. Between the end of the Permian and the beginning of the Triassic it was the most widespread herbivore on the planet. ©Roger Smith

From 14 minutes… Explains Pia Viglietti, researcher at the Field Museum of Natural History in Chicago and lead author of the study: «We thought that, since the marine extinction occurred in a short period of time, the disappearance of life on land also had followed the same pattern, but we discovered that this was not the case”. And this has led scientists to ask a fundamental question: “Is it possible to superimpose the two extinction scenarios, the one for the mainland and the one for the oceans?” The answer was given by Kenneth Angielczyk, co-author of the study and curator of vertebrate paleontology at the Field Museum: “No, these are profoundly different scenarios: something very different happened on land from what happened in the seas”.

We now know that the great extinction event at the end of the Permian led to the disappearance of more than 85 percent of marine species over 100,000 years: it may seem like a very long time to us, but it is not so on the geological time scale. Indeed, it is a very short period of time: if the entire time of the Earth were “1 year”, that extinction would have taken place in no more than 14 minutes. We know of the relative rapidity of this catastrophe due to the study of marine fossils, much more abundant and easier to find than fossils of land animals: the consequence is that, until today, what was always “returned” to terrestrial life he learned about extinction from marine fossils.

… more than two hours! To understand what happened with Viglietti’s land animals, Angielczyk and their colleagues looked at the fossils of 588 four-legged animals that lived in what is now the Karoo Basin in inland South Africa at the time of the Permian extinction event. Paleontologists have developed a statistical model that has made it possible to determine how long it took for a certain species to gradually decrease until it disappeared and how other species stabilized just when the environment seemed to be hostile to life. In this way a profoundly different picture was seen: using the same comparison as before, if the history of life on Earth were compressed into a single year, the Permian extinction wiped out 95 percent of land animals in two hours and twenty minutes.

The mystery. On the one hand we have a hundred thousand years, on the other a million… Why this difference? Paleontologists don’t have a precise answer, but a hypothesis: «Climate changes accumulated over time», explains Viglietti, «and, as regards the marine environment, for a while they were cushioned by the sea without anything happening, until the saturation point was reached: when the balance was broken, the catastrophe was consumed rapidly”. On the mainland, however, the loss of species has gone hand in hand with the progressive degradation of the environment, so the phenomenon has continued over time without ever stopping.

It is a hypothesis that can help us understand what could happen in our day: «The oceans can absorb a lot of carbon dioxide, and even increase in temperature without major consequences, initially», concludes Viglietti: «but when the solvent reaches saturation, the consequences they are sudden and dramatic», from the bleaching of corals to the interruption of the great ocean currents.

The history of the Earth it teaches that the seas could still absorb our excess greenhouse gas emissions into the atmosphere for a while, and in particular carbon dioxide, but at a certain point they will be full, saturated, and they won’t be able to take it anymore! What will happen then? The meltdown will be followed by dramatic and irreversible events on our time scale, in the seas and on land.