The Permian extinction was one of the biggest catastrophes in the long history of the Earth. The biosphere of the planet has lost almost all marine animals and more than 70% of terrestrial representatives. Have scientists been able to understand the causes of extinction and assess its consequences? What theories have been put forward and can they be trusted?
Permian
To roughly imagine the sequence of such distant events, it is necessary to refer to the geochronological scale. In total, the Paleozoic has 6 periods. Perm is a period on the border of the Paleozoic and Mesozoic. Its duration according to the geochronological scale is 47 million years (from 298 to 251 million years ago). Both eras, both Paleozoic and Mesozoic, are part of the Phanerozoic eon.
Each period of the Paleozoic era is interesting and eventful in its own way. During the Permian period, there was an evolutionary push that developed new forms of life, and the Permian extinction of species that destroyed most of the animals of the Earth.
What is the reason for the name of the period
"Perm" is surprisingly familiar title, don't you think? Yes, you read that right, it has Russian roots. The fact is that in 1841 a tectonic structure corresponding to this period of the Paleozoic era was discovered. The find was located near the city of Perm. And the whole tectonic structure today is called the Cis-Ural marginal foredeep.
Mass extinction concept
The concept of mass extinctions was introduced into scientific circulation by scientists at the University of Chicago. The work was carried out by D. Sepkoski and D. Raup. According to statistical analysis, 5 mass extinctions and almost 20 smaller catastrophes were identified. Information for the last 540 million years was taken into consideration, since there is not enough data for earlier periods.
The largest extinctions include:
- Ordovician-Silurian;
- Devonian;
- Permian extinction of species (the reasons for which we are considering);
- Triassic;
- Cretaceous-Paleogene.
All these events took place in the Paleozoic, Mesozoic and Cenozoic eras. Their periodicity is from 26 to 30 million years, but many scientists do not accept the established periodicity.
The Greatest Ecological Disaster
The Permian extinction is the most massive catastrophe in the history of our planet. The marine fauna died out almost completely, only 17% of the total number of terrestrial species survived. More than 80% of insect species died out, which did not happen during other mass extinctions. All these losses occurred in about 60 thousand years, although some scientists suggest that the period of massmora lasted about 100 thousand years. The global losses brought about by the great Permian extinction have drawn the final line - having crossed it, the Earth's biosphere began to evolve.
Restoration of fauna after the greatest ecological catastrophe lasted a very long time. We can say that much longer than after other mass extinctions. Scientists are trying to recreate models that could have led to a mass pestilence, but so far they cannot agree even on the number of shocks within the process itself. Some scientists believe that the Great Permian Extinction 250 million years ago had 3 peak shocks, other scientific schools are inclined to believe that there were 8 of them.
One of the new theories
According to scientists, the Permian extinction was preceded by another massive catastrophe. It happened 8 million years before the main event and significantly undermined the Earth's ecosystem. The animal world became vulnerable, so the second extinction within the same period turned out to be the greatest tragedy. If it can be proved that there were two extinctions in the Permian period, then the concept of the periodicity of mass catastrophes will be in doubt. In fairness, let's clarify that this concept is disputed from many positions, even without taking into account the possible additional extinction. But this point of view still holds scientific positions.
Possible causes of the Perm disaster
Permian extinction still causes a lot of controversy. A sharp controversy unfolds around the causes of environmentalcataclysm. All possible grounds are considered equivalent, including:
- external and internal catastrophic events;
- gradual changes in the environment.
Let's try to look at some of the components of both positions in more detail in order to understand how likely they are to influence the Permian extinction. Photos of confirming or refuting findings are provided by scientists from many universities as they study the issue.
Catastrophe as the cause of the Permian extinction
External and internal catastrophic events are considered to be the most likely causes of the Great Dying:
- During this period, there was a significant increase in the activity of volcanoes on the territory of modern Siberia, which led to a large outpouring of traps. This means that there was a huge eruption of bas alt in a short time in the geological concept. Bas alt is weakly eroded, and the surrounding sedimentary rocks are easily destroyed. As evidence of trap magmatism, scientists cite vast territories in the form of flat stepped plains on a bas alt base as an example. The largest trap area is the Siberian trap, formed at the end of the Permian period. Its area is more than 2 million km². Scientists from the Nanjing Institute of Geology (China) studied the isotopic composition of the rocks of the Siberian traps and found that the Permian extinction occurred precisely during their formation. It took no more than 100 thousand years (before that it was believed that ittook a longer period of time - about 1 million years). The activity of volcanoes could provoke the greenhouse effect, volcanic winter and other processes that are detrimental to the biosphere.
- The causes of the biospheric catastrophe could be the fall of one or more meteorites, the collision of the planet with a large asteroid. As evidence, a crater with an area of more than 500 km (Wilks Land, Antarctica) is given. Also, evidence of impact events was found in Australia (Bedout structure, Northeast of the continent). Many of the resulting samples were later refuted in the process of deeper study.
- One of the possible reasons is a sharp release of methane from the bottom of the seas, which could lead to the total death of marine species.
- The ability of one of the domains of living unicellular organisms (archaea) to process organic matter, releasing large volumes of methane, could lead to a catastrophe.
Gradual changes in the environment
There are several points combined in this category of reasons:
- Gradual changes in the composition of sea water and the atmosphere, resulting in anoxia (lack of oxygen).
- Increase in the dryness of the Earth's climate - the animal world could not adapt to the changes.
- Climate change has disrupted ocean currents and lowered sea levels.
Most likely, a whole range of reasons influenced, since the disaster was massive and occurred in a short period.
The consequences of the Great Dying
The Great Permian extinction, the causes of which the scientific world is trying to establish, had serious consequences. Entire units and classes have completely disappeared. Most of the parareptiles died out (only the ancestors of modern turtles remained). A huge number of species of arthropods and fish disappeared. The composition of microorganisms has changed. In fact, the planet was empty, being dominated by carrion-eating fungi.
After the Permian extinction, the species most adapted to overheating, low oxygen levels, lack of food and excess sulfur content survived.
Massive biospheric cataclysm opened the way for new animal species. The Triassic, the first period of the Mesozoic era, revealed to the world the archosaurs (progenitors of dinosaurs, crocodiles and birds). After the Great Dying, the first species of mammals appeared on Earth. It took 5 to 30 million years for the biosphere to recover.
