He Anthropocene was established in 2016 As a new geological epoch, this is happening with the Holocene that began in the mid-20th century. This new era would be marked by an accelerated mass extinction of species that has been described as the sixth mass event of this type, and the first caused by one of those species: humans. What were these other events like?

0. The big oxidation

Although not usually included in the five great extinctions, it was undoubtedly the first major reversal in biological evolution: between 2,400 and 2,050 million years ago, in the Paleoproterozoic Era, the atmosphere and the surface of the oceans began to fill with oxygen , a gas until then very rare on Earth. It is believed that photosynthetic microorganisms were responsible for this phenomenon known as the Great Oxidation, although whether the main culprits were cyanobacteria or other more primitive microbes is still debated, as are the causes of this drastic drift.

1. Ordovician-Silurian Extinction

For more than 2,000 million years of life on Earth, only unicellular creatures existed, until about 575 million years ago when the first multicellular organisms began to appear, a phenomenon called the Avalon explosion. It was at this point that the main major lineages of fauna were born, from which most of today’s animals descend, although life at that time was still confined to the water and its banks. But about 443 million years ago, and almost suddenly in geological time, 85% of the planet’s species disappeared. One of the theories is a major ice age in the southern supercontinent.

2. Devonian extinction

The Devonian began 419 million years ago, known today as the Fish Age, when these animals grew and diversified until they colonized all aquatic environments. It was also when the earth turned green: plants covered the landscape, forming large forests populated by invertebrates such as millipedes, arachnids, and the first insects.

At the end of the Devonian, a series of extinctions that lasted millions of years began, which together wiped out up to 75% of all species. The gradual nature of the second major extinction in Earth’s history has given rise to multiple hypotheses about its causes, including the usual ones such as volcanism or the impact of a space object.

3. Triassic-Permian Extinction

252 million years ago, which is considered the greatest extinction in Earth’s history, so extensive that it marks the death of one era, the Paleozoic, and the birth of another, the Mesozoic, that we know today as the reign of the dinosaurs. The large amounts of CO2 that caused catastrophic global warming, although the possible impact of a space object is not ruled out. The result was the extinction of more than 85% of marine species in just 100,000 years. And while it marked the final end for some emblematic animals of the Paleozoic Era, such as the few trilobites that had survived the two previous extinctions, the extinction on land could have lasted longer and affected 70% of the fauna, including countless reptiles, amphibians and insects. .

According to a 2021 study, the extinction was followed by a proliferation of bacteria and algae in the water, turning them into a poisonous and uninhabitable soup for hundreds of thousands of years; It took Earth 4 million years to recover, and coral reefs wouldn’t return to their former splendor until 14 million years later. The study’s authors warned that the same thing is happening in the current climate crisis: The excessive discharge of nutrients and the warming of the seas are causing this eutrophication that consumes oxygen from the water, creating dead zones and releasing large amounts of N2O into the water. atmosphere. , a greenhouse gas.

4. Triassic-Jurassic Extinction

The Triassic, the first period of the Mesozoic Era, is a period of 50 million years flanked by two of the great terrestrial extinctions. It was not until the middle of this period that life began to recover the diversity it had before the catastrophe at the end of the Permian. However, another volcanic disaster in the area of ​​what is now the Atlantic Ocean released massive amounts of CO2, leading to global warming and ocean acidification, which were devastating to the biosphere.

5. Cretaceous-Tertiary Extinction

The last of the five great extinctions is undoubtedly the most widely known, as it marked the end of the age of the dinosaurs. However, it’s not entirely accurate to say that the dinosaurs went extinct, as not all of them did. All current birds originated from the group of avian dinosaurs, smaller animals that survived the catastrophe.