Geologically, one of the most catastrophic extinctions in Earth's history, which occurred in the Permian period, lasted literally an instant. According to researchers from the Massachusetts Institute of Technology, 96% of aquatic species and 70% of terrestrial species became extinct in just 60 thousand years. Nothing like this has happened in the history of our planet since then.
Scientists managed to get an amazing figure of 60 thousand years thanks to new, more accurate methods for determining the age of rocks.
“We have an idea of the exact age and duration of the extinction,” said Sam Bowring, professor of geology at MIT. - But how could you kill 96% of all the inhabitants of the oceans for some tens of thousands of years? It looks like an exceptional extinction requires an exceptional explanation.”
About 10 thousand years before the disaster, Earth's oceans were exposed to large amounts of light carbon isotopes. As a result, the water was strongly acidified, and its temperature immediately increased by 10 degrees. It was these events that destroyed most of the marine life, the researchers are confident.
The Permian mass extinction is known to be one of five mass extinctions. The boundary between the Permian and Triassic geological periods was drawn along it (it also separates the Paleozoic and Mesozoic eras). The age of this boundary according to the modern (2012) geochronological scale is 252.2 ± 0.5 million years.
This is one of the largest disasters in the biosphere in the history of the Earth, which led to the extinction of 96% of all marine species and 70% of terrestrial vertebrate species. The disaster was the only known mass extinction of insects, as a result of which about 57% of genera and 83% of species of the entire class of insects became extinct. Because of the loss of this abundance and diversity of species, the recovery of the biosphere took a much longer period of time than other extinction disasters.
The models by which the extinction proceeded are under discussion. Various schools of thought suggest one to three extinction shocks.
Extinction was rapid (lasted no more than 200 thousand years), synchronous at sea and on land, accompanied by massive fires. Presumably, it was caused by a sharp emission of greenhouse gases caused by trap magmatism in the territory of present-day Siberia, which led to significant overheating of the planet and drought. Tropical forests were the first to die, followed by other vegetation, resulting in a sharp increase in erosion and soil loss.
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Currently, experts do not have a generally accepted opinion about the causes of extinction. A number of possible reasons are considered:
- catastrophic events:
- intensification of volcanic activity in Siberia;
- the fall of one or many meteorites, or the collision of the Earth with an asteroid several tens of kilometers in diameter (one of the proofs of this hypothesis is the possible presence of a 500-kilometer crater in the Wilkes Land area);
- sudden release of methane from the seabed;
- the acquisition by archaea (genus Methanosarcina) of the ability to process organic matter with the release of large volumes of methane.
- gradual changes in the environment:
- anoxia - changes in the chemical composition of sea water and the atmosphere, in particular, oxygen deficiency;
- increasing the dryness of the climate;
- changes in ocean currents and / or sea level under the influence of climate change;
The most widespread hypothesis is that the cause of the catastrophe was the outpouring of traps (first, relatively small Emeishan traps about 260 million years ago, then the colossal Siberian traps 251 million years ago), which could entail a volcanic winter, a greenhouse effect due to the release of volcanic gases and other climatic changes affecting the biosphere.
Evidence that asteroid impacts may have triggered a Late Cretaceous catastrophe raises hypotheses that similar events could also cause other mass extinction events, including the Permian extinction, and craters of appropriate sizes are being sought to test these hypotheses.
In Australia and Antarctica, evidence was found for the existence of shock events corresponding to the Permian period: grains of quartz of impact origin, fullerenes with inclusions of inert gases of extraterrestrial origin, fragments of meteorites in Antarctica, and grains containing increased levels of iron, nickel, and silicon - possibly of impact origin. However, the reliability of most of these studies is highly questionable. For example, quartz from Antarctica, believed to be of impact origin, has recently been examined using optical and electron microscopes. As a result, it was revealed that the found samples were formed, most likely, as a result of plastic deformations in solids, and not from impacts during tectonic processes like volcanism.
Several craters (possibly of impact origin), including the Badout structure in northeastern Australia and the hypothetical Wilkes Land crater in western Antarctica, are considered as traces of meteorites that caused the massive Permian extinction. In each of these cases, the cosmic impact hypothesis was not confirmed and was criticized. And in the case of Wilkes Land, the age of these geological formations is not precisely determined and may refer to later periods.
As a result of mass extinction, many species have disappeared from the face of the Earth, whole groups and even classes have become a thing of the past; most of the order of parareptiles (except for the ancestors of modern turtles), many species of fish and arthropods (including trilobites). Marine ecosystems have been rearranged: the role of reef-formers is shifting from bryozoans to corals, and bottom filter feeders from brachiopods to bivalve molluscs.
The cataclysm also hit the microbial world hard.
As a result, our planet has become very empty. Some scientists generally believe that the Earth was at the mercy of fungi, feeding on the remains of dead organisms.
It is believed that the restoration of the biosphere after the mass extinction took about 30 million years, but some scientists conclude that it could have happened in a shorter period of time, about 5-10 million years. During the restoration of the biosphere, opportunistic organisms have become widespread: fungi, bacterial mats, and lymphatic plants Pleuromeia.
The Permian extinction ended the period of prosperity of Synapsids (although a dozen species survived) and Anapsid reptiles, giving way to many animals that remained in the shadows for a long time: the beginning and middle of the Triassic period following Perm was marked by the formation of archosaurs, from which dinosaurs and crocodiles, and subsequently birds …
Those species survived that turned out to be more adapted to new conditions: overheating, lack of oxygen, lack of food, excess sulfur in water, etc. Although, of course, the survival or extinction of many species was accidental. If in the distribution area of this species there was a small area where acceptable habitat conditions were maintained, then the probability of survival was higher. Thus, some plants in Australia have successfully survived the extinction.
In addition, it was in the Triassic that the first mammals appeared. A small part of warm-blooded animal-like tetrapods - cynodonts - survived to the beginning of the Triassic. The cynodonts themselves did not survive the Triassic, but their descendants managed to withstand the Cretaceous extinction, which killed all dinosaurs, and lay the foundation for a new group of animals - mammals, behind which the future of our planet turned out.