250 million years ago, climate change responsible for the great extinction
The Permian extinction
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: around - 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 ocean Tethys, producing a considerable volume of basaltic lavas 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 sea currents, which have led to the progressive extinctions of very many living beings, on the scale of a few million years.
..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 apparently resulted from 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 that would have brutally altered the climate of the planet, have said researchers whose summaries of work appeared in the journal Science dated Friday.
"Based on the geochemical clues we have found, the extinction of marine and terrestrial species seems to have occurred simultaneously" and gradually, explained Peter Ward, a paleontologist from the University of Washington (northwest), responsible for 'one of the research teams.
"Animals and vegetation on land as 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 hints of a sudden catastrophe like the one caused by the fall of an asteroid.
This researcher and colleagues from the University of Washington, the South African National Museum, and the California Institute of Technology, in particular, examined 127 fossilized skulls of reptiles and amphibians discovered in a 300 m sediment core thickness taken from the 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 indices, to establish that the great extinction took place gradually over a period of ten million years followed by a very strong acceleration for five million years.
A second team of paleontologists led by Kliti Grice of Curtin University of Technology in Perth, Australia, analyzed sediments from the same geological era taken from the Australian and Chinese coasts in which they discovered chemical clues showing that the ocean then lacked oxygen and contained many bacteria growing in the sulfur.
These discoveries 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 sulfurous gases from volcanic eruptions.
"I think the temperatures on the globe have become increasingly hot to reach a point which has destroyed all life," said Peter Ward, adding that this phenomenon has been accompanied by a depletion of the oxygen.
In addition, most experts continue to agree that the disappearance of dinosaurs 65 million years ago is explained by the climatic disaster caused by the fall of an asteroid in what today forms the Chicxulub crater in Mexico, near the Yucatan peninsula.