There 250 million years, climate change responsible for the mass 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 is related to the occurrence of various geological phenomena to - 265 Ma, marine regression, key continental shelves of Pangaea; Continental intense volcanic activity (traps Emeishan [China], to - 258 Ma and traps of Siberia, - 250 Ma); a very important activity of the oceanic ridges of the Tethys Ocean, producing a large volume of basaltic lava to cause a transgression affecting the coasts of Pangea, about ten million years. These phenomena would be to correlate to changes in climate and ocean currents, resulting progressive extinction of many living beings, throughout millions of years.
A climate change ...
..and not an asteroid, would have caused the mass extinction of species there 250 million years, according to international research published Thursday in the United States.
After several years of research, these teams paleontologists concluded that the disappearance of 90% of marine species and 75% of the flora and fauna of the land between the late Permian and early Triassic apparently resulted from a warming due to atmospheric greenhouse effect created by volcanic eruptions.
The most commonly accepted theory so far to explain the greatest disaster in the history of life on Earth was the fall of a large meteorite or comet collision with that would abruptly changed the climate of the planet, have researchers indicated that the summary of the work appeared in the journal Science, dated Friday.
"Based on the geochemical indices we have found, the extinction of marine and terrestrial species appears to have occurred simultaneously" and gradually, explained Peter Ward, a paleontologist from the University of Washington in the northwest, responsible for one of the research teams.
"Animals and vegetation on earth and in the oceans have perished during the same period and apparently the same causes, namely too high temperatures and lack of oxygen," he added, noting that he observed little indications of a sudden catastrophe like that which 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, in particular, looked 127 fossilized skulls of reptiles and amphibians found in a sediment core from 300 m thick taken from sedimentary deposits of the Karoo basin in South Africa. These sediments date from the late Permian and early Triassic.
These scientists have been able, through chemical cues, biological and magnetic, establish that the mass extinction took place gradually over a period of ten million years followed by a sharp 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 epoch levied on Australian shores and China where they found chemical evidence showing that the ocean was missing oxygen and contained many bacteria growing in the suffering.
These findings corroborated the results of studies in South Africa and suggest that the Earth's atmosphere was so poor in oxygen and poisoned by hot sulphurous gases from volcanic eruptions.
"I think that the temperatures on the globe have become warmer and warmer to reach a point that has destroyed all life form," said Peter Ward, adding that this phenomenon has been accompanied by a depletion of the " oxygen.
Moreover, most experts continue to agree to say that the disappearance of the dinosaurs there 65 million years is explained by the climate catastrophe caused by an asteroid in this form today Chicxulub crater in Mexico near the Yucatan Peninsula.