American geologists have found deposits of volcanic rocks near the banks of the Tunguska River, whose access to land launched the Great Permian extinction of animals, which killed almost all living creatures 252 million years ago, according to an article published in the journal Nature Communications.
“The heat that was released during the release of these lavas on land led to the fact that neighboring sedimentary rocks threw huge amounts of greenhouse gases into the atmosphere, the volume of these gases was enough to cause a mass extinction.This event was a key point in history The evolution of life on Earth, “says James Muirhead of the University of Syracuse (USA).
Scientists identify the five largest mass extinctions of species in the history of life on Earth. The most significant is the “great” Permian extinction, when more than 95% of all living creatures that inhabited the planet disappeared, including bizarre animals, close relatives of the ancestors of mammals, and a number of marine animals.
There is evidence that at that time large amounts of carbon dioxide and methane were released into the atmosphere and oceans, which dramatically changed the climate and made the Earth extremely hot and arid. As shown by the research of Russian geologists, these emissions came to the surface of the planet in the territory of Eastern Siberia, in the vicinity of the Putoran and Norilsk Plateau, where about 252 million years ago there were powerful outpourings of magma.
As Muirhead says, most scientists today are confident that these outpourings of lava were implicated in the extinction of animals, but the specific mechanism of their action on the climate and ecosystem of the Earth remained a mystery. The reason for this was simple – geologists simply did not have exact data on the age of these breeds and did not know whether these outpourings began before the onset of mass extinction, with or after it.
For example, some excavation results in the territory of Eastern Siberia indicate that outpourings of magma began several dozen or even hundreds of thousands of years before animals began to disappear and ecosystems began to change. This puts all such theories in doubt, since eruptions of this magnitude should cause virtually instantaneous changes in the life of animals and plants.
Blow from the past
Muirhead and his colleagues uncovered this riddle and found the “trigger” of the Permian extinction, conducting excavations in the Tunguska river basin, where the rocks formed during these outpourings lie.
By collecting new samples of igneous rocks, scientists measured the proportion of lead and uranium isotopes in them and found out how and when they came to the surface of the Earth. As it turned out, 252 million years ago there was not one, but two different eruptions. The first, more large-scale, led to the release of about 60% of igneous rocks to the surface, but it did not lead to the extinction of animals and did not cause visible effects.
The second, less noticeable eruption, which occurred approximately 251.9 million years ago, was less noticeable externally, but much more dangerous for life. This outpouring of magma “warmed up” a large layer of sedimentary rocks, lying at the surface, which led to the liberation of huge amounts of CO2, methane and other greenhouse gases into the atmosphere.
The reason for this, as the scientists say, was that these lava flows did not immediately reach the surface of the Earth, but originally moved parallel to it, through cracks between layers of sedimentary and volcanic rocks. As a result, a shallow but very large underground “lake” emerged from the lava, whose area was approximately 50 times larger than that of the present-day Lake Baikal. It heated vast reserves of chalk, coal, oil and other sedimentary rocks and caused them to decompose.
Such a mechanism for the emergence of the Permian extinction, as Muirhead and his colleagues note, indicates that the consequences of the mass eruptions of volcanoes with which other mass extinctions are associated today could depend heavily on the rocks through which their emissions passed. Scientists hope that studying their tracks will help us understand how life evolved in the past and how such events influenced the course of its development.