American geologists found the sediments of the volcanic rocks in the Tunguska River. These volcanic rocks caused the Permian–Triassic extinction event, also known as the Great Dying. It was considered the most mysterious event on the planet. As a result, almost all animals died 252 million years ago.
“Heat from sills exposed untapped, gas-rich sediments to contact metamorphism [the process in which rock minerals and texture are changed by exposure to heat and pressure], thus liberating the massive greenhouse gas volumes needed to drive extinction,” – says James Muirhead, a research associate in the Department of Earth Sciences in in the Syracuse University College of Arts. “Our model links the onset of extinction with the initial pulse of sill emplacement. It represents a critical juncture in the evolution of life on Earth.”
The scientists define the five largest mass extinctions of species in the history of Earth. Permian–Triassic extinction event is considered as the most significant because 95% of living beings inhabited the planet died.
There are several pieces of evidence that during that time a large amount of carbon dioxide and methane were discarded into the atmosphere and ocean. Such an event changed the climate and made Earth hot and dry.
According to the research of Russian geologists, these emissions came to the surface of the planet on the territory of Eastern Siberia near the Putorana Plateau and Norilsk. In these places, the powerful magma effusions took place 252 million years ago.
As James Muirhead said, today most of the scientists are convinced that these magma effusions caused the extinction of the animals. However, the concrete mechanism of infliction upon the climate and ecosystem was a mystery until now. The reason is simple: the geologists did not have any data about the age of these volcanic rocks. Therefore, the experts did not know whether these effusions began before the mass extinction, along with it or after the event.
Hit of the past
James Muirhead and his colleagues solved this mystery and found the trigger of the Permian–Triassic extinction event. They carried the excavations on the territory of Tunguska River, where the volcanic rocks are located.
The scientists collected the samples of the rock types and measured the proportions of the lead and uranium isotopes. Such a way they found out the way and time when magma effusions came on the surface. It turned out that this event took place 252 million years ago. By the way, there were two different eruptions.
The first one was much bigger and made circa 60% of the rock types come to the surface. However, it did not lead to the extinction of the animals.
The second eruption was smaller but more dangerous. It took place approximately 251,9 million years ago and warmed a large layer of the sedimentary rocks. Such a situation caused the massive carbon dioxide emissions and emissions of methane and other greenhouse gases into the atmosphere.
According to the experts, the reason of it was that fact that lava flows came to the surface of Earth, not at the same time, but made such a giant underground “lake” of lava, which warmed the coal stocks, chalk, petrol and other rocks. The “lake” was 50 times larger than Baikal. Thus, all these rocks became to decompose.
James Muirhead and his colleagues notice that the similar mechanism of the appearing of Permian–Triassic extinction event means that fact that the consequences of the mass volcano eruptions could depend upon the rocks the emissions came through. The scientists hope that the exploring of its marks can help to understand how the life evolved in the past.
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