American geologists have found deposits of volcanic rocks off the banks of the Tunguska River, whose landfall triggered the Great Permian Extinction of Animals, which destroyed almost all living things 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 to land led to the fact that the neighboring sedimentary rocks emitted huge amounts of greenhouse gases into the atmosphere. The volume of these gases was sufficient to cause a mass extinction. This event became a key point in the history of the evolution of life on Earth,”says James Muirhead of Syracuse University (USA).
Fiery abyss
Scientists have identified the five largest mass extinctions of species in the history of life on Earth. The most significant is considered the "great" Permian extinction, when more than 95% of all living beings inhabiting the planet disappeared, including bizarre beast-lizards, close relatives of mammalian ancestors, and a number of marine animals.
There is evidence that large amounts of carbon dioxide and methane were released into the atmosphere and oceans during this time, dramatically changing the climate and making the Earth extremely hot and arid. As the studies of Russian geologists show, these emissions came to the surface of the planet in Eastern Siberia, in the vicinity of the Putoran and Norilsk plateaus, where about 252 million years ago the most powerful outpourings of magma occurred.
Muirhead says that most scientists today believe that these outpourings of lava were involved in the extinction of animals, but the exact mechanism of their action on the Earth's climate and ecosystems remained a mystery. The reason for this was simple - geologists simply did not have accurate data on the age of these rocks and did not know whether these outpourings began before the onset of the mass extinction, together with it or after it.
For example, some results of excavations in Eastern Siberia indicate that the outpouring of magma began several tens or even hundreds of thousands of years before animals began to disappear and ecosystems changed. This casts doubt on all such theories, since eruptions of this magnitude should cause virtually instantaneous changes in the life of animals and plants.
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Blow from the past
Muirhead and his colleagues uncovered this mystery and found the "trigger" of the Permian extinction by excavating in the Tunguska River Basin, where the rocks formed during these eruptions lie.
Collecting new samples of igneous rocks, scientists measured the proportion of isotopes of lead and uranium 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, on a larger 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 consequences.
The second, less noticeable eruption, which occurred about 251.9 million years ago, was less visible in appearance, but much more life-threatening. This outpouring of magma "warmed up" a large layer of sedimentary rocks that lay at the surface, which led to the release of huge amounts of CO2, methane and other greenhouse gases into the atmosphere.
The reason for this, scientists say, was that these lava flows did not immediately reach the Earth's surface, but initially moved parallel to it, through cracks between layers of sedimentary and volcanic rocks. As a result, a shallow but very large underground “lake” of lava arose, whose area was about 50 times larger than that of modern Lake Baikal. It heated vast reserves of chalk, coal, oil and other sedimentary rocks and caused them to decompose.
Such a mechanism for the occurrence of the Permian extinction, as Muirhead and his colleagues note, suggests that the consequences of massive volcanic eruptions, with which other mass extinctions are associated today, could strongly depend on which rocks their emissions passed through. Scientists hope that studying their traces will help us understand how life evolved in the past and how such events influenced the course of its development.
Scheme of & quot; work & quot; volcanoes during the Permian extinction. Burgess et al. / Nature Communications 2017
