Extinction is something normal in the history of life. From time to time a species disappears because environmental conditions change, or a new predator appears, or because they lose their ability to compete for food. However, at certain points in Earth’s history there have been mass extinctions , global catastrophes that destroy entire ecosystems and wipe out tens of thousands of species.
They have been so decisive that they have served to define geological history: in 1984 the geologist John Phillips defined the borders that separate the Paleozoic, Mesozoic and Cenozoic because he discovered that in the rock strata above each of these borders there were forms of life that were different from the ones below. It was obvious that if there was a radical change in the species, something catastrophic must have happened.
Of the half dozen mass extinctions that have occurred in the history of the planet (because in the opinion of some, we are immersed in a sixth extinction whose cause is the human being), one has been especially devastating: the Permian extinction , 250 million years ago. years, where it is estimated that 80% of all species then disappeared , including 96% of marine life and 70% of land vertebrates. In short, life was about to disappear from the face of the Earth. For millions of years our planet was an almost lifeless wasteland, a planet in which only the hardest and most resistant living beings, fungi, proliferated. University of Washington astrobiologist Peter Ward, an expert on this moment in Earth’s history known as the Great Dying, has made it very clear: “At the end of the Permian you could see virtually nothing alive.” The Earth needed 30 million years to recover.
No one knows what or what were the causes for such a disaster. Something not surprising, given that it happened 250 million years ago and the vast majority of geological evidence has disappeared or is buried deep in the earth’s crust. So geologists and paleontologists must look for any trace, no matter how small, that gives them clues as to what could have happened. And it is not easy, although in reality only a few phenomena can account for what happened.
It is obvious that only a catastrophic event could trigger it, see excessive volcanism, a meteorite impact… In addition, this short-lived cataclysm had to trigger a whole wave of longer-lasting events, such as acid rain or global warming. Faced with this panorama, geologists can take one of two paths: either they think that there was a dominant factor , if not the only one, that caused the mass extinction and the rest are simple consequences of what happened, or that there was a series of events -some more intense and others less- but that none was a critical factor for extinction. It is what we could call a Murder on the Orient Express style scenario, in honor of Agatha Christie’s novel where there are several murderers and all equally relevant.
It goes without saying that candidates are not lacking: if we talk about asteroids or comets , an impact has been discovered that could be related to the extinction in Brazil, the Araguainha crater; but if we think of intense volcanic activity we must look to Siberia , where evidence has been found that 1.5 million cubic meters of lava flowed from a gigantic crack in the crust. Such an eruption could cause vast tracts of land to burn, a darkening of the sky due to volcanic ash, and a change in climate and acidification of the oceans due to the enormous amounts of carbon dioxide released into the atmosphere. It has been possible to verify that the latter happened after analyzing the calcareous shells of brachiopod fossils, organisms similar to clams, which have been found in the Alps. In short, if the atmosphere was filled with gases such as carbon dioxide, methane and sulfur dioxide, it would have caused a lethal global warming, which together with the depletion of oxygen in the oceans, acid rain and an atmospheric pollution triggered in metals heavy would have triggered extinction . Now, what was the cause of this widespread volcanism? Plate tectonics? The fall of an asteroid? Was this the murderer who shot everything or just an accomplice?
Be that as it may, after analyzing seven layers of volcanic material from southern China, researchers believe that the extinction that marked the end of the Permian occurred in less than 31,000 years, a sigh from a geological point of view. And not only that, but it is suspected that, regardless of the cause, during the following 5 million years there were several waves of extinction, which further depleted the battered biodiversity that would have survived the initial catastrophe. Moreover, in 2019 Chinese scientists found that ocean temperatures reached 40º C, making it impossible for marine life to recover.
