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Five massive mass extinctions on Earth began in the sixth

Numerous scientists estimate that the Earth is at the beginning of a new "mass extinction", a phenomenon that characterizes the disappearance of species in an alarming number for a relatively short time, this time caused by human activities.

In the last 500 million years, the planet has witnessed five times during which, in the blink of an eye of geological history, more than half of all living beings have disappeared.

Overall, more than 90 percent of the species that used to walk, swim, fly, or track the Earth are extinct.

The first mass extinction occurred about 445 million years ago. In the so-called "Ordoviciana-Souluriana extinction", between 60 and 70% of the species disappeared.

It is believed that even this extermination led to a short but very strong ice age.

At that time, the world of the living was mostly in the oceans. Scientists believe that the rapid formation of glaciers froze most of the planet's water and led to a drastic drop in sea levels. Marine organisms, such as sponges and algae, were devoid of nutrients, in addition to mollusks, primitive cephalopods, and fish without a jaw, called ostracoderms.

Then, about 360 to 375 million years ago, the so-called "Kasnodevonskoe extinction" ensued, in which up to three quarters of the living world disappeared. Most of the marine organisms were again killed due to the reduction of oxygen in the ocean.

The most probable causes of this development of events are variations in the levels of the oceans, climatic changes or even impact of asteroids. According to one theory, the expansion of terrestrial vegetation led to the lack of oxygen in the waters. Probably the most famous victim of the "Kasnodevonsky extinction" were the trilobites, arthropods that lived at the bottom of the ocean.

Especially destructive was the "Perm-Triassic extinction", about 252 million years ago. This period, also called "mother of all extinctions", took 95% of the species.

Caused by asteroids and volcanic activity, the biological crisis devastated oceans and lands. Some scientists believe it lasted millions of years, while others believe it lasted only 200,000 years.

It was the only time the insects were massively missing. The last surviving species of trilobites, as well as some species of sharks and fish, also disappeared. On the continent, exterminated by others and by the mosquitoes, more than a meter of reptiles of the herbivores.

The next was the "Trieste-Jurassic extinction" and the disappearance of 70% to 80% of the species due to numerous and not fully explained reasons. According to one theory, the trigger was a massive lava eruption due to the collapse of the Pangeia supercontinent, which was accompanied by the release of large amounts of carbon dioxide that led to rapid climate change. Although some scientists also suspect asteroids, no crater has been found so far.

At the transition of the Triassic period in June, numerous species of large land animals disappeared, including the largest number of archosaurs, dinosaur ancestors and current birds and crocodiles. Most giant amphibian species were exterminated.

For the time being, the last and probably most widely known mass extinction occurred at the end of the Cretaceous period, 66 million years ago, by chance, thanks to the asteroid that hit the area of ​​the current Mexican peninsula of Yucatan and left a huge crater. All non-mobile dinosaurs died, but the largest number of mammals, turtles, crocodiles, toads and birds survived on earth. Sharks, starfish and hedgehogs survived on the seas.

The disappearance of the dinosaur allowed the dissemination of mammals, which led to the formation of homosapiens, a species responsible for a certain sixth mass extinction.

In Paris, a meeting of scientists and diplomats from more than 130 countries is under way, and after 15 years has been making a global assessment of the ecosystem.

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