Causes of extinction of species on earth. Mass extinctions of flora and fauna in the history of the earth

Extinction - a phenomenon in biology and ecology, consisting in the disappearance (death) of all representatives of a certain biological species or taxon. Extinction can have natural or anthropogenic causes. With especially frequent cases of extinction species in a short period of time, one usually speaks of a mass extinction.

The largest extinctions in the history of the Earth

440 million years ago - Ordovician-Silurian extinction — more than 60% of marine invertebrate species have disappeared;
364 million years ago - Devonian extinction - number of species marine organisms decreased by 50%;
251.4 million years ago - "great" Permian extinction , the most mass extinction of all, which led to the extinction of more than 95% of the species of all living things;
199.6 million years ago - triassic extinction - as a result of which at least half of the now known species that lived on Earth at that time died out;
65.5 million years ago - Cretaceous-Paleogene extinction - the last mass extinction that destroyed a sixth of all species, including dinosaurs.
33.9 million years ago - Eocene-Oligocene extinction .

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Ordovician-Silurian extinction (eng. Ordovician extinction - “ Ordovician extinction”) - a mass extinction on the border of the Ordovician and Silurian period, about 450-440 million years ago. 3rd in percentage of extinct genera of the top five extinctions in Earth's history, and 2nd in loss of living organisms

Between 450 and 440 million years ago, with an interval of 1 million years, there were two bursts of extinction. For marine organisms, this is the second largest extinction, second only to the Permian extinction. At that time all famous life took place in the seas and oceans. More than 60% of marine invertebrates died

The immediate cause of extinction appears to have been traffic gondwana to the area south pole. This led to global cooling, glaciation and the subsequent drop in the level of the world's oceans. Ocean boundary retreat has destroyed or damaged habitats along continental coasts

Devonian extinction - mass extinction of species at the end of the Devonian, one of the largest extinctions of flora and fauna in the history of the Earth. The first (and strongest) peak of extinction occurred at the beginning of the Famennian - the last century of the Devonian period, about 374 million years ago, when almost all jawless animals suddenly disappeared. The second impulse ended the Devonian period (about 359 million years ago). In total, 19% of families and 50% of genera became extinct

By the late Devonian, the land was fully developed and inhabited by plants, insects and amphibians, and the seas and oceans were full of fish. In addition, giant reefs formed by corals and stromatoporates already existed during this period. The Euroamerican continent and Gondwana have just begun moving towards each other to form a supercontinent in the future Pangaea. Probably, the extinction mainly affected marine life. The underlying theory suggests that main reason Extinctions in the oceans were caused by changes in the level of the ocean and the depletion of ocean waters in oxygen. It is possible that global cooling or extensive oceanic volcanism acted as an activator of these events, although the fall of an extraterrestrial body, such as a comet, is also quite possible. Some statistical studies of the marine life of that time suggest that the decrease in diversity was due to a decline in the rate of speciation rather than an increase in the rate of extinction.

Possible causes and consequences of extinction:

Since the extinction took place over a long period, it is very difficult to single out a single cause that led to the extinction and even to separate the cause from the effect. deposits sedimentary rocks show that the Late Devonian was a time of change environment, which directly affected living organisms, causing extinction. It was directly responsible for these processes. global change environment which, in turn, could be due to:

meteorite fall

Qualitative leap in the evolution of plants (development of the vascular system of nutrition and reproduction by seeds, which served as a significant increase in plant biomass)

Significant: erosion (due to the development of the root system in plants) and the influx of the border into rivers and seas (due to the decomposition of the colossal mass of plants)

The extinctions were accompanied by widespread oceanic anoxia , that is, a lack of oxygen, which prevented the decay of organisms, and predisposed to the preservation and accumulation of organic matter. This effect, combined with the ability of spongy reef rocks to retain oil, allowed Devonian deposits to be an important source of oil , especially in the US.

A study (McGhee 1996) estimates that 22 percent of all marine animal families (mostly invertebrates) have gone extinct. It is worth considering that the family is a very large taxonomic category, and that the loss of such a large number of creatures means the complete destruction of the diversity of ecosystems. On a smaller scale, losses are even greater, accounting for 57% of genera and at least 75% of non-Carboniferous species.

Mass Permian extinction (informally referred to as The Great Dying - the great extinction, or as the English The Greatest Mass Extinction of All Time - the greatest mass extinction of all time). It marks the boundary between the Permian and Triassic geological periods (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 Ma.

It is one of the largest catastrophes of the biosphere in the history of the Earth, led to the extinction of 96% of all marine species and 70% of terrestrial vertebrate species. The catastrophe was the only known mass extinction of insects, which resulted in the extinction of about 57% of the genera and 83% of the species of the entire class of insects. Due to the loss of such a large number and diversity of species, the restoration of the biosphere took a much longer period of time compared to other disasters leading to extinctions.

Reasons for the crash:

Currently, there is no generally accepted opinion among specialists about the causes of extinction. A number of possible reasons are considered:

catastrophic events:
- increased volcanic activity in Siberia;
- the fall of one or many meteorites, or the collision of the Earth with an asteroid with a diameter of several tens of kilometers (one of the proofs of this hypothesis is the possible presence of a 500-kilometer crater in the area of ​​Wilkes Land);
- sudden release of methane from the bottom of the sea
gradual environmental changes:
- anoxia - changes chemical composition sea ​​water and the atmosphere, in particular oxygen deficiency;
- increasing dryness of the climate;
- changes in ocean currents and/or sea levels under the influence of climate change;

Effects:

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. The extinction of old forms opened the way for many animals , which remained in the shadow for a long time: the beginning and middle of the next one after the Permian, Triassic period was marked by the formation archosaurs from which originated dinosaurs and crocodiles, and later birds . In addition, it is in the Triassic that first mammals .

Triassic-Jurassic extinction marks the boundary between the Triassic and Jurassic periods, 199.6 million years ago and is one of the largest extinctions of the Mesozoic era, deeply affecting life on Earth.

Possible reasons:

Gradual climate change or sea level fluctuations during the Late Triassic. However, this does not explain the sudden extinction of creatures in the ocean.
- An asteroid impact, but there is no dated impact crater whose formation would coincide with the Triassic-Jurassic boundary (the collision responsible for the ring-shaped structure of Lake Manikouagan occurred 12 million years before the Triassic-Jurassic extinction event).
- Massive volcanic eruptions, especially the outpouring of basalt lavas in the Central Atlantic Magmatic Province (CAMP), would release carbon dioxide or sulfur dioxide into the atmosphere, which in turn would cause severe global warming (from the first gas) or cooling (from the second gas).
- Hypothesis about " methane hydrate gun" . Warming due to volcanism and the accumulation of carbon dioxide in the atmosphere led to the release of methane from bottom clathrates. The release of methane, even a stronger greenhouse gas than CO2, has accelerated warming even more, which in turn has led to more methane being released from the ocean floor. This process could lead to a rapid change in global temperature.

Effects:

An entire class of conodonts that made up 20% of all marine families, all the widespread crurotarses (non-dinosaur-like archosaurs), some of the remaining therapsids, and many species from the widespread group of amphibians have completely disappeared. At least half of the now known species that lived on Earth at that time became extinct. This event freed up ecological niches, allowing dinosaurs to dominate from jurassic. The Triassic extinction occurred in less than 10,000 years and occurred just before Pangea began to break apart.

Cretaceous-Paleogene extinction event (Cretaceous-Tertiary, Cretaceous-Cenozoic, K-T extinction) - one of the five so-called. "great mass extinctions", on the border of the Cretaceous and Paleogene period, about 65 million years ago. There is no consensus on whether this extinction was gradual or sudden, which is currently the subject of research.

Part of this mass extinction was dinosaur extinction . Died out with the dinosaurs marine reptiles(mosasaurs and plesiosaurs) and flying pangolins, many mollusks, including ammonites, belemnites and many small algae. In total, 16% of families of marine animals (47% of genera of marine animals) and 18% of families of terrestrial vertebrates perished.

However, most of the plants and animals survived this period. For example, land reptiles such as snakes, turtles, lizards, and aquatic reptiles such as crocodiles have not died out. The closest relatives of the ammonites, the nautilus, survived, as did birds, mammals, corals, and land plants.

Presumably some dinosaurs (triceratops, theropods, etc.) existed in the west North America and in India a few more million years at the beginning of the Paleogene, after their extinction in other places.

The most famous versions of the causes of extinction:

The fall of an asteroid is one of the most common versions (the so-called "Alvarez hypothesis"). It is based mainly on the approximate timing of the formation of the crater Chicxulub (which is a trace of the fall of an asteroid about 10 km in size about 65 million years ago) on the Yucatan Peninsula in Mexico and the time of extinction of most of the extinct species of dinosaurs.

A "multiple impact event" version that involves several consecutive hits.

Supernova explosion or nearby gamma-ray burst.

Collision of the Earth with a comet.

Increased volcanic activity

Sharp drop in sea level

Change in average annual and seasonal temperatures

Sudden jump magnetic field Earth.

Too much oxygen in the Earth's atmosphere.

Rapid cooling of the ocean

Changes in the composition of sea water.

Widespread spread of an infectious disease (epizooty)

Dinosaurs could not adapt to the change in the type of vegetation and were poisoned by the alkaloids contained in the flowering plants that appeared.

Dinosaurs were exterminated by the first predatory mammals, destroying the clutches of eggs and cubs.

A variation of the previous version: the first mammals, reproducing faster than dinosaurs, and also having a more perfect metabolism, could force out reptiles in the course of competition in those ecological niches for which they themselves had little claim, as happened with amphibians before.

Eocene-Oligocene extinction (also known in relation to European fauna as the Great Break (French "Grande Coupure")) - significant changes in the composition of marine and terrestrial flora and fauna. It began at the end of the Eocene epoch - the beginning of the Oligocene epoch, about 33.9 ± 0.1 million years ago. Significantly inferior in scale to the five largest mass extinctions in the history of the Earth.

In the oceans, this extinction was very extended in time and took about 4 million years (the end of the Middle and Late Eocene). According to a number of estimates, the total extinction of marine animals was 3.2%, which is several times higher than the background figure of 0.66%. Terrestrial representatives of the fauna experienced the greatest extinction in two stages.

Hypotheses for the causes of extinction:

Collision with asteroids. According to a number of scientists, a sharp climate change, which led to the extinction of species, was caused by the successive impact of two meteorites that fell in North America - Chesapeake Bay and Siberia - popigay . Meteor impacts caused a sharp drop in temperature, which led to a decrease in the concentration of carbon dioxide in the atmosphere. A number of meteorologists associate the formation of the Antarctic ice sheet with the Oligocene. However, it should be noted that during the fall of asteroids, their impact on the climate on the geological time scale is very short.

Eruption of supervolcanoes. Some scientists claim that of the 47 known supervolcano eruptions, 23 occurred during this period extinction. Huge areas in North America were covered with kilometer-long layers of tuff and ash deposits. Supervolcanic eruptions are understood to be eruptions of a special type that originate from a system of radial fissures when an accumulation of magma uplifts an entire volcanic region rather than a single volcano. Accordingly, the volume of emissions of substances into the atmosphere is many times greater than the volume of emissions from ordinary terrestrial volcanoes.

Climate change during the transition between the Eocene and Oligocene.

Partial shading of the Earth by hypothetical rings (?) of the Earth. In the 1980s, a hypothesis was put forward about the existence at a certain period of the Earth's development of a system of rings similar to those of Jupiter. Further research into the possible rings of the Earth led some scientists to the idea that the shadow cast by the rings could lead to a global cooling of the climate, which in turn caused the extinction of many species of marine organisms in the late Eocene.

In the history of earthly life, scientists have counted up to 11 mass extinctions of flora and fauna, 5 of which greatly changed the appearance of our biosphere. The last of these “Great” extinctions, which occurred 65 million years ago, destroyed 1/6 of all species that existed then (the Cretaceous-Paleogene extinction).

At the same time, together with sea and flying lizards, the most "promoted" order of animals in the paleontological annals of our world disappeared - all dinosaurs.

Modern science does not have comprehensive data on the causes of the last major extinction of species (as well as the previous ones). Among the main suspects are asteroids, volcanoes and internal processes in the terrestrial biosphere. Below, I suggest that you familiarize yourself with the chronicle of terrestrial catastrophes 300 million years long and form your own opinion about the causes of the death of this wonderful detachment of reptiles.

"Mother of all extinctions"

250 million years ago, the largest known extinction in the history of our planet occurred, during the Permian-Triassic catastrophe, 95% of all species of marine and land animals died. Almost all the therapsids that then dominated the land disappeared. Among the few surviving therapsids were the ancestors of cynodonts, whose descendants are all mammals.

The animal-like lizards (synapsids) include the early Permian pelycosaurs (on the left, dimetrodon) and their descendants of therapsids (on the right, gorgonops). In particular, Gorgonopsians are the closest relatives of cynodonts.

The vacated ecological niches of therapsids were occupied by archosaurs, which already in 20 million years will begin to dominate as land predators (dinosaurs and crurotarses).

The main reason for this extinction is usually considered to be the outpouring of Siberian igneous traps at the border of the Permian and Triassic periods. During the formation of the traps, about 4 million km3 of rocks were thrown out, covering an area of ​​2 million km2. The process of outpouring of rocks set off a cascade reaction of global climate change, eventually, presumably, and caused a mass extinction.

The area of ​​the Siberian traps eruption superimposed on the map of modern Russia

"Mysterious" Triassic-Jurassic extinction event

Already after 50 million years, the earth's biosphere had to face another series of mass extinctions. On the border of the Triassic and Jurassic periods, an unknown global cataclysm caught the crurotarzes dominating the land. Having displaced their "cousins" of dinosaurs and mammals, by that time crurotarses had become the main and largest land predators late Triassic.

Some representatives of the late Triassic carnivorous crurotarse

As a result of the catastrophe, the crurotarses shared the fate of the therapsids, giving way to their "cousins" - dinosaurs, which would dominate the land for a long 140 million years. One of the two surviving groups of crurotarsians, the protosuchians, are the direct ancestors of modern crocodiles.

The main versions of this extinction are considered to be the fall of a large asteroid and volcanic activity (Central Atlantic igneous province, CAMP). In the first case, the impact of a 4 km asteroid that formed the 100 km Manicouagan crater in Canada was considered as the cause, but geological dating places its fall by 14 Ma before the Triassic extinction.

Today, the Manicouagan crater has a transverse diameter of 70 km (originally 100 km). Craters of this size usually result from the impact of asteroids with a diameter of about 4-5 km, and do not have long-term consequences for terrestrial fauna and flora

The combined hypothesis received the greatest support. According to her, the CAMP, which caused the outpouring of 2 million km3 of volcanic rock, including a huge amount of CO2, provoked the release of huge bottom ocean "pockets" of methane hydrates through global warming. Methane, being a stronger greenhouse gas than CO2, set off a chain reaction of overheating earth's atmosphere which is believed to have caused mass extinctions.

"Stable" Mesozoic

The period of dominance of dinosaurs on land (the Jurassic and Cretaceous periods of the Mesozoic era) was not at all geologically "quieter" than other periods of earth's history.

183 million years ago there was a large magmatic eruption of the Karoo-Ferar, comparable in scale to the CAMP (2.5 million km3 of igneous rocks). However, this event did not cause any catastrophic consequences for earthly life. The collision with the Earth of a large asteroid about 4 km in diameter passed without serious consequences 167 million years ago - in the middle of the Jurassic period (the destroyed Puchezh-Katunsky crater in Nizhny Novgorod region Russia).

The second mass extinction in the history of dinosaurs occurred on the border of the Jurassic and Cretaceous periods - 145 million years ago. One of many hypotheses links the formation of one of the largest shield volcanoes to this "little Jurassic" extinction. solar system- Tamu's array pacific ocean. However, it is possible that the global effect from the formation of the volcano increased the impact of a 4 km asteroid in the same period of time (Morokweng crater, South Africa). By this time, scientists attribute the appearance of flying dinosaurs - the ancestors of modern birds.

The Tamu massif in the Pacific Ocean is one of the largest extinct volcanoes in the solar system. The total mass of the rocks that make up this ancient volcano is 80% of the mass of the Martian Mount Olympus.

Approximately 12 million years later, already at the beginning Cretaceous, the world's flora and fauna experienced a series of the largest explosive volcanic eruptions in earth's history. The eruption at the beginning of the Hauterivian stage of the Cretaceous period of 8 supervolcanoes released a total of 50,000 km3 of gases and rocks. So the eruption of each supervolcano was on average twice as powerful as the eruption of the Toba supervolcano, which 70,000 years ago caused the “bottleneck” effect.

The fact is also noteworthy in that the "parade" of supervolcanoes was only part of the process of formation of the giant Parana-Etendeka magma traps in South America. The total volume of released rocks amounted to 2.3 million km3. However, as well as 50 million years earlier, these processes did not cause significant fluctuations in the diversity of the terrestrial biosphere.

Ledges formed by basalt flows from the ancient igneous traps of Parana, Brazil

By the end of their epoch, the dinosaurs experienced 3 more major peaks of volcanic activity, which in total erupted 12 million km3 of rocks. During the Cretaceous, the Earth also experienced a whole series of collisions with large asteroids (3 asteroids with a diameter of 1 km, three more 2 km each, and one 3 km in size).

The largest (after Chiksulub) impact crater of the Cretaceous period - Karsky is located in the Nenets Autonomous Okrug of Russia. The impact of a 3 km asteroid 70 million years ago formed a crater with a diameter of about 70 km. The beginning of the decline in the speciation of dinosaurs is attributed to the same period, although the connection between these two events is the subject of discussion.

End of eternity

If we could get to the end of the Cretaceous period, then many of us would not believe that we were in an ancient and alien world. Everywhere dominated angiosperms(flowering), mammals fumbled under their feet, not much different from modern small animals.

They have already managed to divide into placental and marsupials. Then the first primates lived. Snakes and familiar lizards appeared. Ever since the Jurassic period, the forests were teeming with real birds, and their relatives, crocodiles, ambushed animals that came to the river.

Bees are also thought to be partly responsible for the decline in dinosaur diversity in the Late Cretaceous. Evolving about 100 million years ago from pollinating insect-eating wasps, bees, due to their high efficiency, made flowering plants dominant in the terrestrial flora. Herbivorous dinosaurs, not without difficulty, had to slowly change their diet from gymnosperms to flowering plants.

Similar features of our world with that ancient one are limited to the composition of the fauna at the mental watering hole, most of which were still dinosaurs: tyrannosaurids, ceratopsians, hadrosaurs, sauropods, etc. (a more detailed list of the fauna of the end of the dinosaur era).

By the end of the era of dinosaur domination, on the border of the Cretaceous and Paleogene periods, volcanic activity increased in India (then still an island in the middle of the Indian Ocean). The volume of outpouring of the Deccan traps for several hundred thousand years was about 2 million km3, the peak fell on the lava eruption of the Mahabaleshwar-Rajahmundry trap, when during a short (geological) period the volume of emissions amounted to 9 thousand km3 of rocks.

Deccan traps near Mumbai and a map of the area they occupy in India (in blue)

However, according to previous precedents of colossal volcanic activity, we already know that such phenomena in themselves do not necessarily have a catastrophic effect on the earth's climate, and, accordingly, flora and fauna. Most likely, such activity must coincide with exceptional circumstances to trigger the "mechanism" of mass extinction.

Only 6 out of 11 major extinctions coincided in time with active geological processes. Most modern paleontologists are of the opinion that such an "exceptional circumstance" was the impact of a 10 km asteroid in Central America 65 million years ago, during the active phase of the formation of the Deccan traps.

The power of the impact was unprecedented in the history of the Mesozoic era. The released energy was 2 million times greater than the energy of the explosion of the largest thermonuclear charge - the "Tsar of the Bomb". The area of ​​the formed 180 km Chicxulub crater was comparable to the total area of ​​all impact craters formed in the previous 200 Ma.

According to some geological models, the seismic wave from the explosion could be focused at the antipode of the impact crater and cause lava eruptions (or amplify them). By the way, at the antipode point of the collision there was then a region of increased volcanic activity - those same Deccan traps.

The hypothesis does not at all state that volcanism was provoked by an asteroid impact, since the formation of these traps was a purely autonomous process of the earth's lithosphere. It's about exclusively about a possible short-term increase in volcanic activity, since the phenomenon of "seismic focusing" in the particular case of the Earth is very limited.

Chicxulub crater on the Yucatan Peninsula (Mexico). On the left - the crater in the visible range, on the right - with the overlay of a map of gravitational anomalies

Another important condition to start the process of mass extinction is the state of flora and fauna at the time of "force majeure". As before the Permian-Triassic extinction, paleontologists record a decline in the diversity of dinosaurs and other archosaurs in the Maastrichtian stage of the Late Cretaceous (the last 7 million years of the existence of dinosaurs).

This is attributed to global climate change, as the reduction in diversity extended to many other groups of animals and plants (including mammals, birds, and flowering plants). This gave rise to many paleontologists to assume that these two catastrophic events (volcanoes and an asteroid) occurred at an “inconvenient” time for living fauna.

Graph of the frequency of magmatic eruptions (scale on the right) and asteroid impacts (scale on the left) over the past 300 million years (from those confirmed). The former have a relatively long-term effect on the climate (millions of years), the impact of asteroids is "experienced" by nature for several tens of thousands of years. As you can see, natural disasters do not always provoke mass extinctions (red dots at the top are large extinctions, black dots are small ones)

Graph of "short-term" volcanic eruptions over the past 140 million years. Unlike explosive eruptions, lava eruptions are not accompanied by significant explosive releases of molten rocks. The eruption process is relatively calm. The red circle indicates the eruption of the supervolcano Toba, 70 thousand years ago

"The Great Break"

The last of the major extinctions and the fourth for mammals occurred at the border of the Eocene and Oligocene epochs of the Paleogene period 35-30 million years ago. The percentage of extinction of species several times exceeded the "background" level - more than 3% against 0.7% (an order of magnitude weaker than the Cretaceous extinction).

This is the longest of all extinctions of the last 300 million years, lasting 4 million years. The Eocene-Oligocene extinction is associated both with the fall of two large asteroids 35 million years ago (~5 and ~4 km in diameter, respectively), and with significant global volcanic activity 35-29 million years ago (Northern, Central and South America, Africa and the Middle East, see graph above).

100 and 90 km craters Popigay (Russia) and Chesapeake (USA) formed with a short time interval 35 million years ago, and presumably became one of the causes of the Eocene-Oligocene extinction and general cooling of the climate in the Oligocene

"Leviathans"

However, according to many modern biologists, the Eocene-Oligocene extinction was by no means the last. Since the last ice age, 11,000 years ago, the Earth's biosphere began to experience another "Great extinction" in its history (the Holocene extinction).

It has already exceeded the scale of the Eocene extinction, and according to scientists, the species diversity of the fauna of our planet will decrease by 50% at the end of this century (more than 80% for the terrestrial flora). And the reason for this is not at all volcanoes or asteroids, but the appearance and development of a very unusual species of animals - Homo sapiens.

As can be seen in the illustration below, the appearance of a person most often provokes a sharp decrease in the number large mammals(Megafauna). In Africa and South Asia, the effect was weaker as the fauna gradually adapted to coexist with a succession of human species. On the rest of the continents, where the appearance of the "super hunter" was relatively abrupt, the effect of the reduction was much more significant.

Unfortunately, we often forget that the intellectual superiority of man over the rest of wildlife must be accompanied by great responsibility, and not by predatory and often irrational plunder and destruction of its benefits.

Let's hope that things will not come to the "Great anthropogenic extinction", and if it does, then we will not perish in the same abyss into which we will sweep away most of the earth's biosphere ...

Several events in the history of our planet caused the extinction of a significant part of the species that lived at that time.

For a long time paleontologists tried to understand why the dinosaurs became extinct. After all, dinosaurs dominated for over 100 million years. They were the most prosperous class of animals on our planet. And then in some time - maybe in a few thousand years, or maybe in a couple of days - they disappeared. So what happened?

Many explanations have been offered, ranging from the fantastical (dinosaurs were exterminated by little green men in flying saucers that hunted them) to the highly plausible (climate change has destroyed their ecological niche). What I like the most is the explanation that links the extinction of the dinosaurs to the appearance of flowering plants believed to have taken place 65 million years ago, just when the dinosaurs disappeared. The point is that until then the dinosaurs had eaten mostly pine needles and similar foods rich in natural oils, and when they had to switch to grass, they all died of constipation!

In fact, paleontologists rarely focus on the extinction of the dinosaurs alone - after all, 65 million years ago, when the dinosaurs were thrown into dust, 70% of all species on Earth disappeared with them. This event, whatever it was caused, scientists call a mass extinction. We know of many such events, and the mass extinction that befell the dinosaurs was neither the largest nor the latest. Depending on which species extinction is called a "mass extinction", there have been between five and twelve mass extinctions in the last 500 million years. The largest occurred about 280 million years ago, and the most recent about 13 million years ago. Although some scientists believe that the cause of all mass extinctions was the same, the explanations come down mainly to changes in the earth's climate.

In 1980, a father and son team at UC Berkeley stumbled upon a fact that led to the best dinosaur extinction theory to date. Nobel laureate Luis Alvarez and his son Walter have made a thorough analysis of sedimentary deposits dating back to the same period as the extinction of the dinosaurs. In the sediments, they found an abnormally high concentration of the chemical element iridium, a heavy metal similar to platinum. Iridium is extremely rare on the surface of the Earth, since the Earth in its development has long passed the phase of the molten state, when heavy metals sank closer to the center of the Earth. However, iridium is found in much greater quantities in some types of asteroids. So the hypothesis, which is sometimes called Alvarez hypothesis, consisted in the fact that iridium appeared in sedimentary deposits as a result of an asteroid impact on the Earth with a diameter of about 11 km. The main weapon of murder was a cloud of dust, which enveloped the Earth for several years, not letting through Sun rays and thus destroying all life on the planet.

At first, scientists were very skeptical, even hostile, about this statement. But after a few years, evidence began to appear in his favor. For example, geologists, while studying deposits formed during a hypothetical impact, discovered the so-called "impact quartz" - a mineral that could form only when high temperatures and pressure caused by the asteroid impact. Gradually, the opinions of specialists began to lean towards Alvarez's hypothesis. Later, in 1992, the first evidence was found - a crater with a diameter of more than 170 km on the Yucatan Peninsula in Mexico, mostly buried under bottom ocean sediments. Chicxulub Crater (named after a nearby fishing village) is one of the largest craters on Earth, and today it is considered to be the cause of its formation by an asteroid impact, which ended the era of dinosaurs. Recent discoveries showing the presence of isotopes characteristic of asteroids also in a number of other deposits suggest that the mass extinction that occurred 280 million years ago could have been caused by similar causes.

Scientists have now moved the debate about the asteroid impact to other mass extinctions: were they also caused by a collision with some celestial body Or did they have other causes, such as multiple volcanic eruptions or a sudden change in sea level? Today, evolutionary scientists are trying to answer these questions.

According to the research of scientists, for the entire time of the existence of life on Earth, several periods are distinguished during which mass extinctions of living organisms occurred.

Extinction is a phenomenon in biology and ecology, which consists in the disappearance (death) of all representatives of a certain biological species or taxon. Extinction can have natural or anthropogenic causes. With especially frequent cases of extinction of biological species in a short period of time, they usually talk about mass extinction. During mass extinctions, the rate of extinction of species was much higher than usual.

The duration of the extinction is usually estimated to within 1 million years. The causes of mass extinctions are not precisely established, but there are many different theories.

Some scientists are of the opinion that we are living during one of the mass extinctions. It is called the Holocene.

The age of the Earth, according to scientists, is 4.54 ± 0.05 billion years. The earliest indisputable evidence of life on Earth is estimated to be at least 3.5 billion years old.

Scientists identify six largest extinctions in the history of the Earth:

1. Ordovician-Silurian- 440 million years ago, more than 60% of marine invertebrate species disappeared. Third in percentage of extinct genera of the five worst extinctions in the history of the Earth, and second in terms of losses in the number of living organisms.

The main hypotheses of the reasons: prolonged cooling, fluctuations in the level of the world ocean, a flash of gamma radiation, volcanism and erosion.

1. Devonian- 364 million years ago, the number of species of marine organisms decreased by 50%. The first (and strongest) peak of extinction occurred at the beginning of the Famennian - the last century of the Devonian period, about 374 million years ago, when almost all jawless animals suddenly disappeared. The second impulse ended the Devonian period (about 359 million years ago). In total, 19% of families and 50% of genera became extinct.

The main hypotheses of causes: the extinction occurred over a long period, so it is very difficult to single out a single cause. Hypotheses include environmental change, meteorite impact, plant evolution, and erosion effects.

1. great permian- 251.4 million years ago, the most massive extinction of all occurred, which led to the disappearance of more than 95% of the species of all living beings. During this period, 96% of all marine species and 70% of terrestrial vertebrate species became extinct. The catastrophe was the only known mass extinction of insects, which resulted in the extinction of about 57% of the genera and 83% of the species of the entire class of insects. Due to the loss of such a quantity and diversity of species, the restoration of the biosphere took a much longer period of time compared to other disasters. According to researchers at the Massachusetts Institute of Technology, 96% of aquatic species and 70% of terrestrial species became extinct in just 60,000 years.

The main hypotheses of the reasons: environmental change, increased volcanic activity, the fall of meteorites, the release of methane from the bottom of the sea.

1. Triassic- 199.6 million years ago, at least half of the now known species that lived on Earth at that time died out. This event freed up ecological niches, allowing dinosaurs to dominate from the Jurassic onward. The Triassic extinction occurred in less than 10,000 years and occurred just before Pangea began to break apart. Statistical analysis of marine life losses at this time suggests that the decline in diversity was due to a decline in the rate of speciation rather than an increase in extinction.

The main hypotheses of the reasons: a gradual change in climate, the fall of an asteroid, massive volcanic eruptions, the release of methane.

1. Cretaceous-Paleogene- 65.5 million years ago, one sixth of all species died out, including dinosaurs. Along with the dinosaurs, marine reptiles died out, including mosasaurs and plesiosaurs, flying lizards, many mollusks, including ammonites and belemnites, and many small algae. In total, 16% of families of marine animals (47% of genera of marine animals) and 18% of families of terrestrial vertebrates perished. Presumably, some dinosaurs (Triceratops, theropods, etc.) existed in the west of North America and in India for several million years at the beginning of the Paleogene after their extinction in other places.

The main hypotheses of the causes: the fall of an asteroid, a supernova explosion or a nearby gamma-ray burst, a collision of the Earth with a comet, increased volcanic activity, a sharp drop in sea level, a change in average annual and seasonal temperatures, a sharp jump in the Earth's magnetic field, an excess of oxygen in the Earth's atmosphere, a sharp cooling of the ocean , change in the composition of sea water, mass epidemic, change in the type of vegetation, the appearance of the first predatory mammals.

1. Eocene-Oligocene— 33.9 million years ago there were significant changes in the composition of marine and terrestrial flora and fauna. It was inferior in scale to the first five mass extinctions.

The main hypotheses for the causes are: asteroid impact, supervolcano eruption, climate change and partial shading of the Earth by hypothetical Earth rings.

Hypothetically, we are living in the next major extinction period, called the Holocene, which began about 13 thousand years ago with the disappearance of large mammals, the so-called megafauna. It is assumed that extinction occurs mainly due to human activity.

This extinction includes numerous families of plants and animals, including mammals, birds, amphibians, reptiles, and arthropods. 875 extinctions that occurred between 1500 and 2009 have been documented by the International Union for Conservation of Nature and natural resources. The vast majority of cases are not documented. Theoretically, the current rate of extinction could be up to 140,000 species per year.

Most people's knowledge of the mass extinction of animal species begins and ends with the events of the asteroid impact that killed the dinosaurs 65 million years ago. But, in fact, the Earth has undergone many mass extinctions in its history since the first bacterial life appeared about three billion years ago. Today, we are facing a potentially 11th disappearance as global warming causing irreparable harm to the balance of the ecosystems of our planet. In the following paragraphs of the article, you will discover a chronological list of the 10 largest mass extinctions of animal species in the history of life on Earth.

1. Great oxygen crisis (2.3 billion years ago)

A major turning point in the history of the planet's life occurred about 2.5 billion years ago, when bacteria developed the ability to photosynthesize, that is, to use sunlight and carbon dioxide for energy generation. Unfortunately, the main by-product is oxygen, which was toxic to anaerobic (oxygen-free respiration) organisms that appeared on Earth as early as 3.5 billion years ago. Two hundred million years after the evolution of photosynthesis, enough oxygen accumulated in the atmosphere led to a mass extinction of anaerobic life (with the exception of deep-sea bacteria) of the planet.

2 Snowball Earth (700 million years ago)

More a hypothesis than a proven fact, Snowball Earth claims that our planet's entire surface completely froze between 700 and 650 million years ago, causing the extinction of most photosynthetic life. While the geological evidence for the hypothesis is strong, the causes of this phenomenon are hotly debated, with possible contenders including volcanic eruptions, solar flares and mysterious fluctuations in the Earth's orbit.

Assuming what actually happened during the Snowball Earth period, then most likely life on our planet came closest to complete, irrevocable extinction.

3. Ediacaran extinction (542 million years ago)

Not many people know about the Ediacaran period, and for good reason: this expanse of geologic time (from 635 million years ago to the cusp of the Cambrian) was only officially named by the scientific community in 2004. Since the Ediacaran period, fossil evidence has been preserved of simple, soft-bodied multicellular organisms that preceded the hard animals of the late Paleozoic. However, in deposits dating to the end of the Ediacaran, fossils disappear and there is a gap of several million years before new fossils appear.

4. Cambrian-Ordovician extinction (488 million years ago)

You may have heard of the Cambrian explosion: the appearance in the fossil record, about 500 million years ago, of numerous strange organisms, most of which belonged to arthropods. But most likely, you are not familiar with - the mass extinction, which led to the disappearance of a huge number of marine animals, including trilobites and brachiopods. The most likely explanation is a sudden, inexplicable decrease in the oxygen content of the world's oceans, when life had not yet reached land.

5. Ordovician-Silurian extinction (447-443 million years ago)

The Ordovician extinction actually consists of two separate mass extinctions: the first occurred about 447 million years ago, and the second 443 million years ago. By the time these two "pulses" were over, marine invertebrate populations (including brachiopods, bivalves and corals) had dropped by as much as 60%. The reasons for the Ordovician-Silurian extinction are still a mystery. To possible reasons include: gamma-ray bursts, volcanoes and erosion.

6. Devonian extinction (375 million years ago)

Like the previous extinction, the extinction of many species of animals most likely consisted of a series of "impulses" that stretched over about 25 million years. During this time, about half of the world's marine organisms became extinct, including many of the ancient fish. No one is still sure about the causes of the Devonian mass extinction. Perhaps it happened under the influence of a meteor impact or serious environmental changes caused by the world's first land plants.

7. Permo-Triassic extinction (250 million years ago)

One of the largest mass extinctions in the history of the Earth, the extinction became a real global catastrophe, destroying an incredible 95% of marine and 70% of land animals. The damage was so colossal that it took about 10 million years to restore life. It would seem that an event of this magnitude could only have been caused by the impact of an asteroid. However, the most probable causes are: intense volcanic activity or sudden release of toxic amounts of methane from the seafloor.

8. Triassic-Jurassic extinction (200 million years ago)

The K-T extinction (see next paragraph) brought about the end of the dinosaur era, while the Triassic extinction made their long dominance possible. By the end of this mass extinction(the exact cause of which is still being discussed), the largest, land amphibians were wiped off the face of the Earth, along with most of the archosaurs and therapsids. The path was cleared for dinosaurs who occupied free ecological niches during the Jurassic and Cretaceous periods.

9. Cretaceous-Paleogene extinction or K-T extinction (65 million years ago)

There is probably no need to retell a familiar story, but still: 65 million years ago, a two-mile diameter asteroid crashed into the Yucatan Peninsula, Mexico, raising thick clouds of dust around the world, which led to a terrible environmental disaster. Many believe that it was the explosion of the asteroid that killed all the dinosaurs, but in fact it only provoked natural disasters throughout the planet, as a result of which, at the junction and periods, dinosaurs, pterosaurs and marine reptiles died out.

10. Quaternary extinction (50,000-10,000 years ago)

The mass extinction was caused (at least in part) by humans, and led to the extinction of most large mammal species, including mammoths, saber-toothed tigers, diprotodonts, and giant beavers. While many believe that these animals were extirpated by the early Homo sapiens, there are other reasons, including climate change and the inexorable destruction of habitual habitats, followed by deforestation by the first farmers.