250 million years ago, climate change responsible for the great extinction
The extinction of the Permian
The Permian extinction is the largest mass extinction that affected the biosphere.
It occurred there 250 million years and marks the boundary between the Permian and the Triassic, so the boundary between the Paleozoic era (Paleozoic) and the secondary era (Mesozoic). It is marked by the disappearance of 95% of marine species (mainly coastal: corals, brachiopods, echinoderms, ...) and also on the continents by the decrease in many plant and animal groups, including insects.
Although the scarcity of geological layers that limit and no precise paleontological data complicate the work of scientists in establishing a precise chronology of events and the relationship between the different causes and biological consequences, one scenario is offers.
This crisis would be related to the occurrence of various geological phenomena: towards - 265 Ma, a marine regression, affects the continental shelves of Pangea; intense continental volcanic activity (Emeishan traps [China], at - 258 Ma, then Siberian traps, at - 250 Ma); a very important activity of the oceanic ridges of the Tethys Ocean, producing a considerable volume of basaltic lava at the origin of a transgression affecting the coasts of Pangea, over ten million years. These phenomena should be correlated with changes in climates and marine currents, having led to the progressive extinctions of a great many living beings, on the scale of a few million years.
Climate change ...
..and not an asteroid, would therefore have caused the great extinction of species 250 million years ago, according to international research published Thursday in the United States.
After several years of research, these teams of paleontologists concluded that the disappearance of 90% of marine species and 75% of terrestrial flora and fauna between the end of the Permian and the beginning of the Triassic was apparently the result of a warming. atmospheric due to a greenhouse effect created by volcanic eruptions.
The most commonly accepted theory so far to explain the greatest catastrophe in the history of life on Earth was the fall of a large meteorite or the collision with a comet which would have suddenly changed the planet's climate, have reported researchers whose summary of work appeared in the journal Science dated Friday.
"Based on the geochemical evidence that we have found, the extinction of marine and terrestrial species appears to have occurred simultaneously" and gradually, explained Peter Ward, a paleontologist at the University of Washington (northwest), responsible for one of the research teams.
"Animals and vegetation on land and in the oceans perished during the same period and apparently from the same causes, namely too high temperatures and lack of oxygen", he added, adding that he observed little signs of a sudden catastrophe like the one that would have been caused by the fall of an asteroid.
This researcher and colleagues at the University of Washington, the South African National Museum, and the California Institute of Technology, among others, examined 127 fossilized reptile and amphibian skulls found in a 300m sediment core. thickness taken from sedimentary deposits of the Karoo Basin in South Africa. These sediments date from the end of the Permian and the beginning of the Triassic.
These scientists were able, thanks to chemical, biological and magnetic clues, to establish that the great extinction took place gradually over a period of ten million years followed by a very strong acceleration over five million years.
A second team of paleontologists led by Kliti Grice from Curtin University of Technology in Perth, Australia, analyzed sediments from the same geological epoch taken from the coasts of Australia and China in which they found chemical clues showing that the ocean then lacked oxygen and contained many bacteria growing in sulfur.
These findings corroborated the results of studies in South Africa and tend to indicate that the Earth's atmosphere was then poor in oxygen and poisoned by emissions of hot sulphurous gases from volcanic eruptions.
"I think the temperatures on the globe have become hotter and hotter to reach a point that has destroyed all life," said Peter Ward, adding that this phenomenon has been accompanied by a depletion of the oxygen.
Moreover, most experts continue to agree that the disappearance of dinosaurs 65 million years ago can be explained by the climatic catastrophe caused by the fall of an asteroid in what today forms the Chicxulub crater in Mexico, near the Yucatan peninsula.