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[EN VIDÉO] Interview: is the mystery of the extinction of the dinosaurs finally elucidated? Scientists have always struggled to find a consensus explaining the extinction of the dinosaurs. Even if the most widely accepted theory is that of a meteorite, there are still gray areas today. Futura-Sciences interviewed Éric Buffetaut, paleontologist, to shed some light on the matter.
The end of the Permian, about 252 million years ago, represents a critical period in the history of life on Terre. It is indeed the most important biological crisis, which saw the disappearance of nearly 90% of species marine species and more than 70% of terrestrial species.
The causes of this extinction are mainly attributed to the volcanism intensive Stairs from Siberia and possibly other volcanoes recently identified, which has profoundly changed the chemistry of the oceans and caused a global warming catastrophic, resulting in the establishment of toxic environmental conditions for the vast majority of living beings in the oceans. However, little is still known about the mechanisms that led to thespecies extinction living on land.
Sulfate aerosols in quantity in the atmosphere at the end of the Permian
In a new study, a team of Chinese and American scientists has therefore attempted to untangle the physico-chemical causes and mechanisms behind the disappearance of many terrestrial species. After taking and analyzing more than 1,000 meters of sedimentary cores to reconstruct the environmental conditions of the Permian, the scientists discovered that this period was associated with significant climatic disturbances caused by the presence ofaerosols sulphate in theatmosphere. Short periods of cooling, similar to volcanic winterswould indeed have succeeded within a global and long-term pattern of extreme global warming.
Acid rain, volcanic winters and warming: the combo for a mass extinction
The study, conducted in the Sydney Basin, Australia, shows that the disappearance of continental species coincides with a clear change in atmospheric composition. The measurements indeed indicate a significant increase in the atmospheric concentration of sulphates, in connection with the dispersion of large quantities of sulphate aerosols from the Siberian Trapps eruption, in progress at that time. The presence of these aerosols would have resulted in rains ofsulfuric acid, in parallel with significant climatic variations. The aerosols formed from the sulfur of volcanic origin are indeed well known to be causing brief volcanic winters preceding longer periods of global warming. These brief drops in temperature are related to the ability of aerosols to reflect the light from soleilthus preventing theenergy sun to reach the ground.
Sulphate aerosols are also the cause of other phenomena, this time leading to an increase in temperatures: a deterioration of the ozone layer and a warming of the middle atmospheric layers by absorption radiation infrared.
The extinction on land would have started 200,000 to 600,000 years before that in the oceans
The destruction of ecosystems par sulfuric acid rain and climatic disturbances would have combined to cause a global and severe deterioration of the terrestrial environment, leading to the disappearance of very many species living on the continents.
This extinction of terrestrial species would have preceded the extinction of marine species by 200,000 to 600,000 years. The results of this study have been published in the journal Earth and Planetary Science Letters.
Permian-Triassic: mass extinction due to rising temperatures?
Between Permian and trias252 million years ago, life on Earth experienced themass extinction the deadliest. Many studies have addressed environmental disturbances in the ocean environment, but on the continents the question remained open. New results show that during this period, South Africa experienced a very strong increase in temperature. This discovery explains the significant extinction of continental communities of tetrapods.
CNRS article published on November 18, 2015
The biological crisis at the end of the Permian (between -299 Ma and -252 Ma approximately) was the most lethal among all those that have punctuated the history of the Phanerozoic, the period of Earth’s history (or aeon) covering the last 541 million years. In just a few hundred thousand years, the biosphere lost at least 80% of marine genera and 70% of families of terrestrial tetrapods, i.e. animals vertebrates lung-breathing whose skeleton has two pairs of limbs (amphibians, reptiles, mammals and birds).
The origin of this rapid mass extinction has been the subject of several hypotheses. For many specialists, it would have been caused by events concomitants such as major volcanism (the Siberian traps) or the massive release of methane, caused by the source from permafrost or the destabilization of clathrates marins. Another hypothesis would indicate that this global extinction was caused by a progressive degradation of the terrestrial environment rather than by instantaneous events on the scale of geological times.
Reconstruction of the atmosphere of the Permian-Triassic boundary
The team of paleontologists and French geochemists (laboratory of Geology of Lyon: Earth, Planets and Environment, CNRS, ENS de Lyon, Lyon 1 University) and South Africans attempted to answer this question by studying the wildlife South African Permian-Triassic. Teeth and bones of therapsids (the reptiles mammaliens), amphibians, parareptiles and archosauriforms (ancestors of crocodiles) from different deposits were analyzed to determine their oxygen isotopic composition (18O/16O).
The scientists then applied the following principle to their data: the average temperature of theair local determines the relative amount of isotopes oxygen contained in rainwater drunk by animals. These isotopic compositions are recorded within the bones and teeth of the animal during their growth and are most often preserved during fossilization. The researchers were thus able to reconstruct the average air temperatures of the living environment of South African tetrapods around the limit Permian-Triassic.
The results show that the average temperatures of the late Permian increased sharply, by 16 ± 10°C, over a duration not more than half a million years old. This fast global temperature increase medium annual Atmospheric changes have strongly modified the different living environments and can explain the disappearance of many marine and terrestrial species.
The results of this research have been published in Gondwana Research on October 26, 2015.
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