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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 the University of California at Berkeley stumbled upon a fact that led to the creation of the best this moment dinosaur extinction theories. Nobel Laureate Luis Alvarez and his son Walter conducted a thorough analysis of sedimentary deposits, the formation of which dates 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.
Ecology
Life on Earth is always fighting for survival. Animals live in constant stress to get enough food and adapt to their environment.
Some animals that are not good at adapting to change experience hardship, starvation, stop breeding, and eventually die out. Throughout the history of our planet, life has taken on new forms, which were immediately tested for survival.
Why did mass extinctions happen?
When the climate and environment changed greatly, many living beings that could not adapt to the new conditions died. Mass extinctions of species have occurred more than once. With such a phenomenon, life forms disappeared without a trace, leaving behind neither fossils nor descendants. Mass extinctions have taken place since the dawn of life on Earth.
All the animals that live on the planet today are just the descendants of those creatures who were lucky, and they were able to adapt to the changed world. We invite you to look into the distant past and learn about the 10 most serious mass disappearances flora and fauna on our planet.
1) Ediacaran mass extinction
During the Ediacaran period, complex beings first began to take shape. Tiny bacteria evolved into more complex life forms - eukaryotes, some of which began to form groups in order to increase the chances of finding food and avoiding the fate of someone else's prey. Most of these creatures did not leave anything behind, since they did not possess a skeleton. They were soft-bodied and completely decomposed after death, not preserved in fossils.
The first simple creatures
Only in very rare cases were creatures from the time of Ediacarus able to reach us in fossils, for example, if the animal was left lying in soft mud, which hardened very quickly, so an imprint was left on it. These few fossils tell us about the presence in the seas and oceans strange creatures, which resembled modern worms, sponges and jellyfish.
These animals depended on oxygen, just like you and me. The level of oxygen in the atmosphere began to fall 542 million years ago. That's when the mass extinction began. More than 50 percent of the living beings of the planet died. A huge number of dead bodies of living beings have rotted into fossil fuels.
The reason why oxygen levels have dropped is not yet known to scientists. However, this extinction also had positive consequences: it served as the impetus for the Cambrian Explosion, an unexpected variety of complex creatures that were more complex than simple worms.
2) Cambrian-Ordovician extinction
During the Cambrian period, life flourished on Earth. Living beings that appeared during the time of Ediacarus remained basically unchanged for millions of years, but after the onset of the Cambrian, life forms began to develop quite quickly, a great variety of unseen living beings evolved. Exotic crustaceans and trilobites have become dominant. Shellfish and giant insect-like marine arthropods filled the seas. These creatures had hard outer shells, thanks to which they have come down to us in the form of fossils.
Ice Age caused extinction
Life flourished on Earth until suddenly (from a geological point of view) 40 percent of all living things on the planet suddenly disappeared 488 million years ago. Those who managed to survive struggled to cope with the harsh conditions environment. What led to the mass extinction of this period, scientists do not know.
According to one theory, at that time there was ice Age, or rather, the coldest part of it. For the last 11 thousand years, the so-called "Interglacial". The extreme drop in temperature has likely led to the death of a huge number of species. It was this mass extinction that marked the boundary between the end of the Cambrian and the beginning of the Ordovician.
3) Ordovician-Silurian extinction
Life on Earth began to flourish again in a period called the Ordovician. Nautiloids (primitive octopuses), trilobites, corals, sea stars, eels and spongefish filled the oceans. Plants began to gradually get out on land. Gradually, life became more difficult.
The second largest mass extinction of species
443 million years ago, more than 60 percent of life on Earth died in the second-worst mass extinction in history. This extinction was associated with the abrupt onset of the ice age, which resulted in lower levels of carbon dioxide. Much of the waters that were home to vast numbers of living things have frozen over or become covered in ice caps and glaciers, resulting in lower oxygen levels.
It is believed that a burst of gamma rays from space destroyed the ozone layer and the ultraviolet radiation of the Sun began to escape to the surface of the planet, which destroyed most of the plants. Fortunately, some people managed to survive, but it took another 300 million years for the planet to fully recover.
4) Mass Extinction Lau
After the Ordovician-Silurian extinction event, the Silurian period began. Life was again restored to the planet and at this time the first sharks and bony fish, most of which are very similar to modern ones. Mosses and small plants began to grow freely on land along the coast, and some arthropods evolved into spiders and centipedes, which adapted to dry air and began to live among plants along the coast.
Variety of marine life
Giant sea scorpions were very diverse, trilobites began to dominate. 420 million years ago, there was a dramatic climate change that wiped out about 30 percent of species. Atmospheric gases have changed in proportions, which for many animals has become uninhabitable and poisonous. The reasons for this event are unknown.
Life on the planet experienced serious difficulties until the end of the Silurian period and until the beginning of the Devonian period, when evolution managed to produce completely different models of life that began to flourish and feel great.
5) The Late Devonian Mass Extinction
During the Devonian period, some species of fish developed fins, which they began to use as limbs, allowing them to crawl on land. These living creatures eventually evolved into reptiles and amphibians. In the seas, giant coral reefs were filled with fish, including sharks, and other marine life, some of which fed on trilobites.
Successful sharks
Trilobites have ceased to dominate the water for the first time in 100 million years since they appeared. In fact, the sharks of this period were so successful that they no longer needed to change much. Some modern sharks look exactly like their distant Devonian ancestors.
Land plants began to produce seeds and reached great variety. More complex plant species evolved on land, and soil appeared for the first time in Earth's history. Strange forests appeared with 8-meter mushrooms, which today we can only see in science fiction films. However, 374 million years ago, 75 percent of all this amazing living creatures died out. This again was due to a change in the composition of the atmosphere, probably due to intense volcanic activity, or due to a meteorite fall.
6) The Disappearance of Carboniferous Rainforests
The Devon period was followed by the Carboniferous period. Several land animals by this time had developed the ability to lay eggs on land, which allowed them to live anywhere, and not depend on coastal waters where they used to lay their eggs, as turtles do today. Flying insects appeared. Sharks were enjoying their golden age and the few trilobites that survived the last extinction are becoming rarer and rarer.
Coniferous trees of Carbon have come down to us
Giant trees and huge rainforests began to cover most of the land of our planet, increasing the oxygen content in the atmosphere to 35 percent. By comparison, today our atmosphere contains only 21 percent oxygen. Coniferous trees Carboniferous have remained virtually unchanged today.
305 million years ago, there was a short but sudden ice age caused by a drop in carbon dioxide to record levels. big forests began to die, and with them many land animals. At that time, about 10 percent of all living beings on the planet disappeared. The trees began to rot, compact, which ultimately led to the formation of deposits of coal, so this period was called the Carboniferous.
7) Mass Permian Extinction
After the giant rainforests disappeared, the most successful animals that lay eggs remained on land. They very quickly assumed dominant positions while other species were still recovering. A large number of the most diverse reptiles and synapsids appeared, which resembled mammals and were their ancestors.
The worst catastrophe on earth
252 million years ago there was a catastrophe that the Earth has never seen before or since. The changes followed a meteorite fall or volcanic activity that changed the composition of the atmosphere in a radical way. Between 90 and 99 percent of all living beings on Earth died. This is the largest mass extinction in the history of the planet.
If we compare it with the extinction of species, which is caused by human activity, then in our history, we are responsible for the death of only 1,000 species of animals. Since today there are about 8 million known species animals, this means that only 0.01 percent died out. This is nothing compared to what happened during the Permian Mass Extinction.
8) Triassic-Jurassic extinction
After the devastation of the Permian period, reptiles again took dominant positions. Dinosaurs appeared. Dinosaurs did not occupy a leading position and at that time were no larger than horses. Their descendants became famous and scary creatures that we all know about.
The beginning of the death of dinosaurs
All large dinosaurs, tyrannosaurs, stegosaurus, triceratops, and giant long-necked sauropod dinosaurs appeared in the Jurassic and Cretaceous period s. 250 million years ago, 65 percent of the living things of the Triassic period died out, including all large land animals. Many dinosaurs survived due to their small size.
Most mass extinctions lasted about a million years, but this one happened in just 10,000 years. It was probably caused by intense volcanic eruptions that released huge amounts of carbon dioxide or sulfur dioxide into the atmosphere, which led to climate change.
9) Late Jurassic Mass Extinction
During the Jurassic period, giant marine reptiles such as famous plesiosaur dominated the oceans. The pterosaurs were the masters of the sky, and the dinosaurs were the masters of the earth. Stegosaurs, long diplodocus, and carnivorous allosaurian dinosaurs became widespread. Conifers, cycads, ginkgoes and ferns made up most of the forest vegetation. Smaller dinosaurs acquired feathers, the first birds began to appear.
The death of the inhabitants of the seabed
By 200 million years ago, about 20 percent of all this life suddenly disappeared from the fossil record, mostly marine species. Shellfish and corals were widely distributed, but as a result of this event, they almost disappeared. The few who managed to survive gradually populated the seas over the next few million years. This mass extinction did not particularly affect land animals, only a few species of dinosaurs disappeared.
The reason for the extinction of marine animals is a matter of dispute in the scientific world, however, according to the leading theory, there is a possibility that tectonic plates oceans have sunk a bit, making the oceans deeper. Most of the marine life was adapted to shallow water, so it began to die, moving further and further away from the surface.
10) Cretaceous-Paleogene Extinction
This is the most famous mass extinction of species. After the Jurassic period ended, dinosaurs continued to multiply and evolve in the subsequent period - the Cretaceous. These animals began to take on the appearance that almost all modern children are familiar with. But most importantly, it was during the Cretaceous period that life finally finally regained strength after an earlier Ordovician-Silurian extinction.
The death of dinosaurs
The number of species has only now reached the Ordovician level for the first time, a period that took place 300 million years before the Cretaceous. Synapsids eventually evolved into small, rodent-like creatures that were the first true mammals.
65 million years ago, a huge meteorite collided with Earth in what is now Mexico, destroying the atmosphere and causing terrible global warming, resulting in the disappearance of 75 percent of living beings.
This meteorite contained a high concentration of iridium, a rare element on Earth. All the earth's rocks that existed 65 million years ago contain a thin layer of iridium, which was left as a result of a meteorite impact. Only a few small reptiles and mammals managed to survive. Mammals replaced dinosaurs and became the dominant land animals on the planet.
The rapid extinction of many mammal species today may be a sign of the impending sixth mass extinction in the history of the Earth, but the situation is not too late to "turn around", scientists say in an article published in the journal Nature. However, before that, the world had already experienced as many as five such catastrophes. Let's see how and when it was.
1. Ordovician-Silurian extinction
The very first mass extinction of animals occurred about 450-440 million years ago. It is impossible to name the exact cause of extinction, but most scientists are inclined to believe that the movement of Gondwana, a huge supercontinent that included almost all of the Earth's land, was to blame.
And all because Gondwana is a giant continent, from which both Africa and South America, and Australia, and Antarctica, - lay down in a drift and headed exactly to South Pole. Water boundaries have changed, and with them the usual ranges of all kinds of brachiopods and molluscs. It all ended with global cooling - water and land. What is today the Sahara desert was then a continuous glacier. The ice significantly changed the terrain: the water level in the ocean dropped sharply. In a word, 60% of marine invertebrates could not pass on their genes.
2. Devonian extinction
It happened 374 and 359 million years ago. The Devonian extinction consisted of two peaks, during which the Earth lost 50% of all existing genera and almost 20% of all families. During the Devonian extinction, almost all agnathans disappeared (only lampreys and hagfish have survived to this day).
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, has made the Devon rocks an important source of oil, especially in the United States.
3. Great Permian extinction
The same mass extinction of animals that has ever happened on our planet. Some scientists call the Permian extinction the greatest mass extinction of all time. About 250 million years ago, 70% of all land animals disappeared. In the ocean, things were even worse - 96% of marine species died. During the Great Permian extinction, more than 57% of genera and 85% of insect species died. This is the only known extinction that affected insects.
In view of the loss of such quantity and variety species recovery of the biosphere took a much longer period of time compared to other catastrophes leading to extinctions.
After the Permian Extinction animal world recovered 30 million years (some scientists believe that the restoration of the biosphere lasted 5 million years). Animals that had previously been in the shade more widely spread widely. strong species. So, this time is considered the period of formation of archosaurs (ancestors of modern crocodiles and extinct dinosaurs). Birds also originated from them, which could not have existed if not for the Great Permian extinction.
4. Triassic extinction
The Triassic extinction happened 200 million years ago. About 20% of all marine animals died, many archosaurs (which became widespread after the Permian extinction), and most species of amphibians. Scientists have calculated that half of all animals known to us that lived at that time died during the Triassic extinction.
A feature of the Triassic extinction is considered to be transience. It happened within 10 thousand years, which is very fast on a planetary scale. At this time, the disintegration of the supercontinent Pangea into separate continents began. It is possible that the reason for the breakup was a large asteroid that changed the weather on the planet, causing extinction. But there is no evidence of this theory, so far not a single large crater of the Triaric period has been found.
Today in science there are several versions of the extinction that happened. The most common hypothesis is the so-called. "methane hydrate gun", which is the most plausible. Due to volcanism and the accumulation of carbon dioxide in the atmosphere, huge amounts of methane began to be released from bottom clathrates. The toxic emissions of this nasty greenhouse gas played a role trigger for a sharp global warming, which destabilized the climate on the planet and became the cause of total Achtung.
5. Cretaceous-Paleogene extinction
The most famous extinction occurred about 65 million years ago. It is famous for the fact that dinosaurs died out on Earth at that time. More than 15% of families of marine animals and 18% of families of land animals also died.
Many explanations have been offered, ranging from the fantastic (the dinosaurs were exterminated by little green men in flying saucers that hunted them) to the highly plausible (climate change has destroyed their ecological niche). The most famous theories say that the Earth collided with a large asteroid or fell into the radiation zone from a supernova explosion.
Most interesting explanation, connects the extinction of the dinosaurs with the appearance of flowering plants, which is believed to have occurred 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!
Another very interesting theory is that they were exterminated by the first mammals that destroyed the clutches of dinosaurs, preventing them from multiplying. This is supported by the fact that some dinosaurs lived for quite a long time on the territory of modern North America and India, where perhaps "dangerous" mammals appeared later.
In total, there are five stages of mass extinctions of animals on Earth. The most famous completely wiped out the dinosaurs, but that was not the biggest disaster. The largest extinction deprived the Earth of 95% of all animals, which made it possible for the emergence of completely new species, which formed the modern zoosphere.
Let's find out more about them.
1. Ordovician-Silurian extinction
The very first mass extinction of animals known to us occurred about 450-440 million years ago. It is impossible to name the exact cause of extinction, but most scientists are inclined to believe that the cause was the movement of Gondwana, a huge supercontinent that included almost all of the Earth's land.
And all because Gondwana - a giant continent, from which Africa, South America, Australia, and Antarctica later “broke off” - fell into a drift and headed exactly to the South Pole. Water boundaries have changed, and with them the usual ranges of all kinds of brachiopods and molluscs. It all ended with a global cooling of water and land. What is today the Sahara desert was then a continuous glacier. The ice significantly changed the terrain - the water level in the ocean dropped sharply. In a word, 60% of marine invertebrates could not pass on their genes.
2. Devonian extinction
It happened 374 and 359 million years ago. The Devonian extinction consisted of two peaks, during which the Earth lost 50% of all existing genera and almost 20% of all families. During the Devonian extinction, almost all agnathans disappeared (only lampreys and hagfish have survived to this day).
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, has allowed Devonian rocks to be an important source of oil, especially in the United States.
3. Great Permian extinction
The most mass extinction of animals that has ever happened on our planet. Some scientists call the Permian extinction the greatest mass extinction of all time. About 250 million years ago, 70% of all land animals disappeared. In the ocean, things were even worse - 96% of marine species died. During the Great Permian extinction, more than 57% of genera and 85% of insect species died. This is the only known extinction that affected 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 leading to extinctions.
After the Permian extinction, the animal world was restored for 30 million years (some scientists believe that the restoration of the biosphere lasted 5 million years). Animals that had previously been in the shadow of stronger species spread widely. So, this time is considered the period of formation of archosaurs (ancestors of modern crocodiles and extinct dinosaurs). Birds also originated from them, which could not have existed if not for the Great Permian extinction.
4. Triassic extinction
The Triassic extinction happened 200 million years ago. About 20% of all marine animals died, many archosaurs (which became widespread after the Permian extinction), and most species of amphibians. Scientists have calculated that half of all animals known to us that lived at that time died during the Triassic extinction.
A feature of the Triassic extinction is considered to be transience. It happened within 10 thousand years, which is very fast on a planetary scale. At this time, the disintegration of the supercontinent Pangea into separate continents began. It is possible that the reason for the breakup was a large asteroid that changed the weather on the planet, causing extinction. But there is no evidence for this theory. So far, not a single large crater of the Triaras period has been found.
Today in science there are several versions of the extinction that happened. The most common hypothesis is the so-called "methane hydrate gun", which is the most plausible. Due to volcanism and the accumulation of carbon dioxide in the atmosphere, huge amounts of methane began to be released from bottom clathrates. The toxic emissions of this unpleasant greenhouse gas played the role of a trigger for dramatic global warming, which destabilized the planet's climate and caused total extinction.
5. Cretaceous-Paleogene extinction
The most famous extinction occurred about 65 million years ago. It is famous for the fact that dinosaurs died out on Earth at that time. More than 15% of marine animal families and 18% of land animal families also perished.
Many explanations have been offered, ranging from the fantastic (the dinosaurs were exterminated by little green men in flying saucers that hunted them) to the highly plausible (climate change has destroyed their ecological niche). The most famous theories say that the Earth collided with a large asteroid or fell into the radiation zone from a supernova explosion.
The most interesting explanation links the extinction of the dinosaurs to the appearance of flowering plants, which is believed to have occurred 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!
Another very interesting theory is that dinosaurs were exterminated by the first mammals, who destroyed their masonry, preventing them from reproducing. This is supported by the fact that some dinosaurs lived for quite a long time on the territory of modern North America and India, where, perhaps, "dangerous" mammals appeared later.
6. Modern extinction
Researchers from Stanford University claim that the Earth is currently experiencing one of the early stages of another mass extinction. They shared their observations in a review published in an issue of the scientific journal Science. Their publication caused a wide response and attracted the attention of many popular science portals, such as "LiveScience".
According to scientists, the planet is now experiencing the peak of biodiversity in 3.5 billion years of existence of life on it. However, alarm signals began to arrive long before the start of the industrial revolution: since 1500, about 320 species of terrestrial vertebrates have become extinct. And the populations of the remaining species have declined by a quarter. Moreover, of the living vertebrates, about 33% of species are endangered. The situation is especially dangerous with representatives of megafauna - elephants, giraffes, hippos and other large animals.
Despite the fact that there are not so many large animals on the planet, their disappearance is accompanied by catastrophic consequences. So, in Kenya, in the territories where elephants, giraffes and zebras used to live, rodents found shelter. And this, in turn, contributes to the uncontrolled eating of grass and shrubs by them. The result of this is soil compaction, and as a result, a decrease in productivity, and subsequently desertification of vast areas. And the population of rodents that has become huge carries many diseases. Since there are no predators, there is no one to control the number of rodents and destroy sick individuals.
Scientists have not forgotten about invertebrates: over the past 35 years, their number has decreased by 45%. This trend is especially dangerous in light of the fact that it is insects that pollinate about 75% of the world's food crops. In addition, insects play an important role in the cycle nutrients and decomposition of organic matter. In the United States, about $4.5 billion annually is spent on combating predators that destroy such insects, which helps to realize the scale of the problem.
“In a global sense, extinction represents the loss of a particular ecosystem. But now extinction certain types directly threatens people. While there is time to try to change something,” says Professor Rodolfo Dirzo, who is one of the authors of the review.
A previous study on the sixth mass extinction was published in the journal Nature. Then scientists were sure that the mass extinction had not yet begun, but would definitely happen in the next 2 thousand years. as the most early term researchers called 300 years. Be that as it may, people should try to change the current situation now.
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:
- 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.
- Devonian- 364 million years ago, the number of species 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 completed Devonian(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.
- 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.
- 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 jurassic. 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.
- 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 close 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 magnetic field Earth, an excess of oxygen in the Earth's atmosphere, a sharp cooling of the ocean, a change in composition sea water, a mass epidemic, a change in the type of vegetation, the appearance of the first predatory mammals.
- 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.
