Science has proven that the risk of extinction is real and in fact There have been five such global extinctions over 4.5 billion years.that is, as soon as the Earth starts to spin.
While the idea that a giant space rock could destroy the planet in minutes is shockingly threatening, there are many other reasons that could lead to the complete collapse of fragile life on Earth. Some are related to the dynamics of our planet; as glaciations, climate changes or sudden changes in sea level, as well as the activation of large volcanoes. Other potential threats relate to changes in ecosystems; such as when an epidemic spreads or when different species fight for survival in the same area.
After five previous extinctions (including the famous extinction of the dinosaurs 65 million years ago), the planet is now facing the sixth: the human-made one in several ways.
These have been five extinctions on our planet.
Ordovician-Silurian Extinction (439 million years ago)
It is considered It was the second most intense of the five mass extinctions ever recorded, but the first in chronological order. In this period, which lasted between 500,000 years and 1 million years, 85% of species extinct, all in the seas. Brachiopods and bryozoans were among the hardest hit, along with the trilobite, conodont, and graptolite families. Although there were two theories trying to explain what was happening on the planet at the time, the causes are still being investigated so much flora and fauna saw its end.
The oldest and most accepted of the theories, The great supercontinent Gondwana began to move aimlessly around the planet.. In this extinction with two phases, there was a first moment when the supercontinent could move from Ecuador to the South Pole. Glaciers formed on it, which lowered the sea level. The freezing of the earth caused changes in currents that stopped feeding the seas as before.
The second phase of this mass extinction occurred at the end of this ice age, when the supercontinent moved towards the equator again, melting the glaciers, changing sea currents once again, and once again changing the level of the seas.
However, in recent years there has been talk of another theory to look at an extraterrestrial phenomenon. According to this theory, the explosion of a nearby supernova and the corresponding pulse of gamma rays could have swept the Earth for about ten seconds, depleting some or all of the ozone layer and killing aquatic life. .
Devonian-Carboniferous Extinction (367 million years ago)
The Devonian was a period of great diversity and prosperity in the oceans, during which numerous marine species emerged. In terrestrial waters, jawed fish such as the fearsome 10-metre-long Dunkleosteus, some sponges, many mollusks and bivalves or large coral reefs began to swim. It is not in vain that this period is also known as the “Age of Fishes”, since it was an absolute reign that lasted for 70 million years.
But this explosion of decent life also brought its end. 83% of species extinct in 3 million years. It mainly affected marine species (like the first).
This extinction is different because there was an extreme mortality in benthic marine organisms, lasted for a long time – about 20 million years – and did not occur in a single event, but split into two, more commonly known as the Kellwasser event and the Hangenberg. Activity.
It is believed that it may have been caused by climate change, which caused different phases of warming and cooling.as well as changes in ocean composition. On the other hand, it is believed that the cause may be a complex event of volcanism. The impact of meteorites cannot be ruled out, as several impact craters have been found to coincide with the period.
Permian-Triassic extinction (251 million years ago)
If there was a devastating mass extinction, it was in the Permian.. At this stage of life, large amphibians and the first reptiles appeared. For the first time, land animals colonized the world, and sea animals were once again in full swing. But in just a million years, everything changed. Only 3% of species survived ecological collapse. in it About 95% of marine species and about 70% of terrestrial vertebrate species disappeared. Due to the resulting low biodiversity, it took a long time for life to recover from this disaster.
The causes of biological hekatom are still unknown. At the moment, Several hypotheses are competing: extreme volcanism, the impact of a large asteroid, and the release of large amounts of greenhouse gases. Trapped on the ocean floor in the form of methane hydrates.
Meanwhile, there is evidence that a large meteorite hit Antarctica, intense volcanic activity occurred, and large quantities of highly toxic hydrogen sulfide were released into the sea. Together, these three events explain the origin of this mass extinction. The liberation of many ecological niches allowed dinosaurs to assume the dominant role in the later Jurassic period.
Triassic-Jurassic extinction (210 million years ago)
Thousands of sea and land species (including the ancestors of dinosaurs) were accustomed to navigating the great continent of Pangea. However, the pieces of this continent puzzle began to separate to set course towards different parts of the planet, and massive volcanic activity emerged from the depths of the Earth.
Intense eruptions at that time may have caused climate change that killed 76% of species. about the planet.
And big eruptions would have ejected enormous amounts of greenhouse gases such as sulfur dioxide (SO2) or carbon dioxide (CO2) that would quickly and devastatingly change the global climate. But the sudden change may have been towards cold rather than warming, because the ejected aerosols could have reached the troposphere, completely blocking the Sun’s light and preventing the Earth from warming.
Experts agree that this mass extinction event is actually a combination of smaller periods of mass extinctions that have occurred over the past 18 million years. The disappearance of most species allowed dinosaurs to flourish and take over the planet.
Cretaceous-Paleogene extinction (65 million years ago)
This is extinction Best known for killing dinosaurs 66 million years agoWhen an asteroid with a diameter of 12 kilometers struck what is now the Gulf of Mexico.
The impact of this meteorite was responsible for the extinction of 75% of the species on Earth. and the complete extermination of the dinosaurs. But when these large reptiles disappeared, mammals had the opportunity to multiply. The effects of the collision lasted for a month, but the extinction took much longer. The Earth was covered with a dust cloud that remained in the atmosphere for 18 months and prevented plants from performing photosynthesis by taking sunlight.
The trophic chain then collapsed, Because herbivores had no plants to feed on. and therefore carnivores had no way of surviving either. It also didn’t help that the Earth’s average temperature rose by 14 degrees Celsius, which caused sea level to rise more than 300 meters (due to melting glaciers), which not only changed ocean currents and the circulation of nutrients (which greatly harms life at sea), but it flooded most of the continents.
Towards the sixth extinction, the first of which was man-made
Man has completely changed the planet for his own benefit. His high stamina combined with his mechanical abilities gave him the ability to survive almost anywhere on the planet. But to achieve this, it did not hesitate to cause irreparable harm to the rest of the species living within it.
For now, large mammal species or megafauna have been the hardest hit. with this new extinction, because at the end of the last ice age, 80% of species weighing more than 1,000 kilos had disappeared. Today, it is estimated that one in eight bird species, one in four mammal species, one in three amphibians and 70% of all plants are endangered due to human activities and anthropogenic climate change.
The difference between the current era and the other five mass extinctions that the Earth has suffered is speed. normally as these events occur over thousands of years.
At the current rate, 18% to 35% of 1,103 animal and plant specimens could be extinct by 2050By the end of the century, extreme living conditions could have caused the extinction of more than half of the species on our planet.
Contact address of the environment department: [email protected]