Perm extinction has become one of the largest disasters 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. Did scientists manage to understand the causes of extinction and evaluate its consequences? What are theories put forward and can they be trusted?
Perm period
To roughly imagine the sequence of such distant events, it is necessary to turn to the geochronological scale. In total, the Paleozoic totals 6 periods. Perm is a period on the border of the Paleozoic and Mesozoic. Its duration on 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. In the Permian period there was an evolutionary impulse that developed new forms of life, and the Permian extinction of species, which destroyed most of the animals of the Earth.
What is the name of the period associated with
Perm is a surprisingly familiar name, doesn't it seem to you? Yes, you were not mistaken, it has Russian roots. The fact is that in 1841 a tectonic structure was discovered corresponding to this period of the Paleozoic era. The find was located near the city of Perm. And the entire tectonic structure today is called the Ural marginal trough.
The concept of mass extinctions
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 disasters were identified. Information for the last 540 million years was taken into consideration, since there are insufficient data for earlier periods.
The largest extinctions include:
- Ordovician-Silurian;
- Devonian
- Permian extinction of species (the causes of which we consider);
- Triassic;
- Cretaceous-Paleogene.
All these events occurred in the Paleozoic, Mesozoic and Cenozoic era. Their periodicity is from 26 to 30 million years, but many scientists do not accept the established frequency.
Greatest environmental disaster
Perm extinction is the most massive disaster in the history of our planet. Marine fauna has died out almost completely, only 17% of the total number of terrestrial species has survived. Over 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 scholars suggest that the period of mass pestilence lasted about 100 thousand years. The global losses caused by the great Permian extinction have drawn the final line - having crossed it, the biosphere of the Earth began evolution.
The restoration of the fauna after the greatest environmental disaster lasted a very long time. It can be said that it is much longer than after other mass extinctions. Scientists are trying to recreate models by which mass pestilence could occur, but so far they cannot even converge in the number of shocks within the process itself. Some scientists believe that the Great Permian extinction 250 million years ago had 3 peak tremors, while other scientific schools are inclined to believe that there were 8.
One of the new theories
According to scientists, the Permian extinction was preceded by another massive disaster. It happened 8 million years before the main event and significantly undermined the Earth’s ecosystem. The fauna became vulnerable, so the second extinction within one period was the greatest tragedy. If it is possible to prove that two extinctions occurred in the Permian period, then the concept of the frequency of mass disasters will be called into question. In fairness, we 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 a scientific position.
Possible causes of Perm disaster
Perm extinction still causes a lot of controversy. Acute controversy revolves around the causes of environmental cataclysm. As equivalent, all possible grounds are considered, including:
- external and internal catastrophic events;
- gradual changes in the environment.
We will try to consider some of the components of both positions in more detail in order to understand how likely they are to affect Permian extinction. Photos of confirming or denying finds are provided by scientists at many universities as they study the issue.
Disaster as a cause of Permian extinction
External and internal catastrophic events are considered to be the most probable causes of the Great Extinction:
- During this period, there was a significant increase in the activity of volcanoes in the territory of modern Siberia, which led to a large outpouring of traps. This means that there was a huge eruption of basalt in a short time in the geological concept. Basalt is slightly susceptible to erosion, 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 basalt base as an example. The largest trap area is the Siberian Trapp, formed at the end of the Permian period. Its area is more than 2 million km². Scientists at the Nanjing Institute of Geology (China) conducted a study of the isotopic composition of the rocks of the Siberian traps and established that Permian extinction occurred precisely during their formation. It took no more than 100 thousand years (before that it was believed that it took a longer period of time - about 1 million years). The activity of volcanoes could provoke a greenhouse effect, volcanic winter and other processes that are detrimental to the biosphere.
- The causes of the biosphere disaster 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 is given (Wilkes Land, Antarctica). Also evidence of shock events found in Australia (Bedout structure, Northeast continent). Many of the samples obtained were later refuted in the course of a deeper study.
- One of the possible reasons is the sharp release of methane from the bottom of the seas, which could lead to the total death of marine animal species.
- A catastrophe could result in one of the domains of living unicellular organisms (archaea) being able to process organics, releasing large volumes of methane.
Gradual changes in the environment
In this category of reasons, several points are combined:
- Gradual changes in the composition of sea water and the atmosphere, resulting in anoxia (lack of oxygen).
- Increased dryness of the Earth’s climate - the animal world could not adapt to the changes.
- Climate change resulted in disturbances in ocean currents and a decrease in sea level.
Most likely, a whole range of reasons influenced, since the disaster was massive, and occurred in a short period.
The Consequences of the Great Extinction
The great Permian extinction, the reasons for 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, falling under the control of carrion fungi.
After the Permian extinction, species survived that were maximally adapted to overheating, low oxygen levels, lack of food, and excessive sulfur content.
The massive biosphere cataclysm paved the way for new species of animals. Triassic, the first period of the Mesozoic era, revealed to the world of archosaurs (progenitors of dinosaurs, crocodiles and birds). After the Great Extinction, the first mammalian species appeared on Earth. The restoration of the biosphere took from 5 to 30 million years.