In the history of earthly life, scientists count up to 11 mass extinctions of flora and fauna, 5 of which greatly changed the face of our biosphere. The last of these “Big” extinctions that occurred 65 million years ago, destroyed 1/6 of all then existing species (Cretaceous – Paleogenic extinction). Then, along with sea and flying lizards, the most “propelled” detachment of animals in the paleontological annals of our world — all dinosaurs — disappeared.

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 earth's biosphere. Below, I suggest that you familiarize yourself with the chronicle of terrestrial catastrophes 300 million years long and make your own opinion about the causes of the death of this wonderful detachment of reptiles.

“Mother of all extinctions”

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

Early Permian pelicosaurs (dimetrodon on the left) and their descendants of therapsids (gorgonops on the right) are referred to beast-lizards (synapsids). In particular, the gorgonops are the closest relatives of the cynodonts. The


released ecological niches of the terapsid were occupied by archosaurs, which already in 20 million years will begin to dominate as land predators (dinosaurs and krotorza).

The main reason for this extinction is usually considered the outpourings of igneous Siberian traps on the border of the Permian and Triassic period. During the formation of the trap, about 4 million km3 of rocks were thrown, covering an area of ​​2 million km2. The outpouring of rocks triggered a cascading reaction of global climate change as a result, presumably, which caused massive extinction.

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

"Mysterious" Triassic-Jurassic extinction

Already after 50 million years, the terrestrial biosphere had to face another series of mass extinctions. On the border of the Triassic and Jurassic periods, an unknown global cataclysm found krurotarzov dominating on land. Having supplanted their "cousins" of dinosaurs and mammals, krurotars by that time became the main and largest land predators of the late Triassic.

Some representatives of the predatory krurotars of the late Triassic


As a result of the catastrophe, the krurotars shared the fate of the terapsid, giving way to their "cousins" - dinosaurs, which will dominate the land for 140 million years. One of the two surviving groups of krurotarsov - protozuchia, are the direct ancestors of modern crocodiles.

The main versions of this extinction are the fall of a large asteroid and volcanic activity (Central Atlantic igneous province, CAMP). In the first case, the impact of 4 km of the asteroid, which formed 100 km of Manicuagan crater in Canada, was considered as the cause, however, geological dating attributes its decline by 14 million years to the Triassic extinction.

Today Manikuagan Crater has a transverse diameter of 70 km (originally 100 km). Craters of this size usually occur when asteroids with a diameter of about 4-5 km fall, and do not have long-term consequences for the terrestrial fauna and flora.


The combined hypothesis received the most support. According to it, the CAMP, which caused the outflow of 2 million km3 of volcanic rock, including a huge amount of CO2, provoked the release of huge oceanic “pockets” of methane hydrates through global warming. Methane, being a stronger greenhouse gas than CO2, launched a chain reaction of overheating of the Earth's atmosphere, which, presumably, caused mass extinctions.

"Stable" Mesozoic

The period of dominance of dinosaurs on land (Jurassic and Cretaceous periods of the Mesozoic era) was not at all geologically “calmer” than other periods of earthly history.
183 million years ago there was a large magmatic outpouring of Karu-Ferar, comparable in magnitude to the CAMP (2.5 million km3 of igneous rocks). However, this event did not cause however catastrophic consequences for earthly life. A major asteroid collision with Earth about 4 km in diameter 167 million years ago, in the middle of the Jurassic period (the destroyed Puchezh-Katunsky crater in the Nizhny Novgorod region of Russia), took place without serious consequences .

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 the many hypotheses that is associated with this "minor Jurassic" extinction is the formation of one of the largest shield volcanoes in the solar system - the Tamu massif in the Pacific Ocean. However, it is possible that the global effect of the formation of the volcano intensified the impact of a 4 km asteroid in the same period of time ( Morokweng Crater , South Africa). To 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 composing this ancient volcano is 80% of the mass of the Martian Mount Olympus


About 12 million years later, already at the beginning of the Cretaceous, the world flora and fauna survived a series of the largest explosive volcanic eruptions in earthly 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. Thus, the eruption of each supervolcano was on average twice as powerful as the eruption of the Toba supervolcano, which caused the “bottleneck” effect 70,000 years ago .

The fact is also notable for the fact that the “parade” of supervolcanoes was only part of the process of formation of the giant magmatic traps of Parana Etenedek in South America. The total volume of released rocks amounted to 2.3 million km3. However, like 50 million years earlier, these processes did not cause significant fluctuations in the diversity of the terrestrial biosphere.

The ledges formed by basalt flows of the ancient magmatic traps of Parana, Brazil


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

The largest (after Chiksulub) impact crater of the Cretaceous period - Karsky is located in the Nenets Autonomous District of Russia. A strike of 3 km of the asteroid 70 million years nazat formed a crater with a diameter of about 70 km. The same period includes the beginning of a decrease in dinosaur speciation, 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, many of us would not believe that we were in an ancient and alien world. Angiospermous plants (flowering) dominated everywhere, mammals fussed 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 lizards familiar to us appeared. Since the Jurassic period, forests were teeming with real birds, and their relatives crocodiles ambushed the animals that came to the river.

Bees are also considered partly responsible for reducing the late Cretaceous dinosaur diversity. Evolving about 100 million years ago from wasps that fed on insect pollinators, bees, due to their high efficiency, made flowering plants dominant in the terrestrial flora. Not without difficulties, herbivorous dinosaurs had to slowly change their diet from gymnosperms to flowering plants.


Similar features of our world with that ancient one are limited by the composition of the fauna of the mental watering hole, most of which were still dinosaurs: tyrannosaurids, ceratops, hadrosaurs, sauropods, etc. (more detailed list of 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 in India (then an island in the middle of the Indian Ocean) increased. The outflow of the Deccan traps over several hundred thousand years amounted to about 2 million km3, the peak fell on the lava eruption of the Mahabaleshwar-Rajamandri trap, when during a short (geologically) period, the volume of emissions amounted to 9 thousand km3 of rocks.

Deccan traps near Mumbai and a map of their area of ​​India (in blue)


However, according to previous precedents of colossal volcanic activity, we already know that such phenomena alone do not necessarily have a catastrophic effect on the Earth’s climate, and, accordingly, flora and fauna. Most likely, such activity should coincide with exceptional circumstances in order to launch 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 10 km of an asteroid in Central America 65 million years ago, during the active phase of the formation of the Deccan Traps.

The impact power was unprecedented in the history of the Mesozoic era. The released energy was 2 million times higher than the energy of the explosion of the largest thermonuclear charge - "King of the bomb." The area of ​​the formed 180 km Chiksulub crater was comparable with the total area of ​​all impact craters formed in the previous 200 million years.

According to some geological models, the seismic wave from the explosion could focus at the antipode of the impact crater and cause lava eruptions (or strengthen them). By the way, at that time the antipode of the collision was a region of increased volcanic activity - those same Deccan traps. The hypothesis does not at all claim that volcanism was triggered by the impact of an asteroid, since the formation of these traps was a purely autonomous process of the earth's lithosphere. We are talking 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 .

Chixulub Crater on the Yucatan Peninsula (Mexico). On the left is a crater in the visible range, on the right is a map of gravitational anomalies


Another important condition for starting 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 decrease in the diversity of dinosaurs and other archosaurs in the Maastrich tier of the Late Cretaceous (the last 7 million years of the existence of dinosaurs). This is associated with a change in the global climate, since the reduction in diversity also extended to many other groups of animals and plants (including mammals, birds, and flowering plants). This gave rise to many paleontologists to suggest that these two catastrophic events (volcanoes and an asteroid) occurred at a time "inconvenient" 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 (of the 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) A


graph of “short-term” volcanic eruptions over a deposition of 140 Ma. Unlike explosive, lava eruptions are not accompanied by significant explosive emissions of molten rocks. The eruption process is relatively calm. The red circle indicates the eruption of the super volcano Toba, 70 thousand years ago

"The great turning point"

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 Ma ago. The percentage of extinction of species several times exceeded the "background" level - more than 3% versus 0.7% (an order of magnitude weaker than the Cretaceous extinction). This is the longest of all extinctions of the last 300 million years lasted 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 (North, Central and South America, Africa and Middle East, see chart above).

100 and 90 km Crater Popigay (Russia) and Chesapeake (USA), formed with a short time interval 35 million years ago, and supposedly 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 not the last. Since the last ice age, 11,000 years ago, the Earth’s biosphere began to experience another “Great Extinction” in its history ( 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 animal species - a rational person.

As can be seen in the illustration below, the appearance of a person most often provokes a sharp decrease in the number of large mammals (Megafauna). In Africa and South Asia, the effect was weaker as the fauna gradually adapted to coexistence.with gradually changing types of people. On other continents, where the appearance of a “super hunter” was relatively sharp, the effect of reduction was much more significant


. Unfortunately, we often forget that the intellectual superiority of a person over the rest of wildlife should be accompanied by great responsibility, and not by predatory and often irrational plunder and destruction of its benefits . Let’s hope that the matter will not reach the “ Great anthropogenic extinction ”, and if it does, we will not perish in the same abyss into which we will sweep a large part of the terrestrial biosphere ...

Well, dinosaurs continue to be part of the terrestrial fauna in the form evolutionarily successful birds. The family relationships of birds with dinosaurs, their differences and similarities will be discussed in the next review.