All living beings we know today -including us- they represent only a small part of everything that has ever existed. It is estimated that 99% of the species that have inhabited the planet in the last 3,500 million years they have disappeared.
Fossil and geological records have provided scientists with enough evidence to identify five of the events responsible for such a high mortality rate. These are massive extinctions, that is, the disappearance of at least 75% of the planet’s species in the blink of a geological eye, which can range from thousands to millions of years.
Each mass extinction ended a geological period of the planet with a sequence of deadly calamities. The surviving species, in turn, thrived on what was left, exploding in diversity and territory. We are the result of this process.
Discover the five mass extinction events known to scientists:
1 – Late Ordovician
Occurring 443 million years ago, the event happened thanks to two major planetary climate changes. First, The polar ice caps advanced, drastically altering ocean currents and creating a harsh climate in the equatorial and mid-latitude regions.
The species that managed to survive the first blow succumbed to the second: a flash melt, causing another severe change in ocean circulation and global climate. 86% of the species and 57% of the existing genera are extinct.
2. The end of the Devonian
Not all mass extinction events are fast. this took 20 million years to occur. Between 359 and 380 million years ago, a series of unexpected climate changes occurred on the planet, including the so-called Hangenberg crisis.
The cause of these changes is uncertain, and although the most accepted explanation is related to high volcanic activity, there are hypotheses that it could even be the result of a supernova (star explosion) near the solar system. About 75% of species and 35% of genera are extinct.
3. Late Permian
251 million years ago, another event could have been triggered by intense planetary volcanic activity, particularly in Siberia. The eruptions spewed out toxic gases, acidified the oceans and destroyed the ozone layer, letting in deadly solar radiation.
This event is believed to have occurred over a period of 50,000 years and to 96% of species and 56% of genera have disappeared. The forests were so destroyed that for a long time there was no material to burn, creating a “coal hole” in the geological record.
4. The end of the Triassic
Volcanoes are relentless. Again, 201 million years ago, massive eruptions in a region that would become the Atlantic Ocean caused climate change on the planet, eliminating about 80% of the species and 47% of the genera.
This episode allowed the surviving dinosaurs to explode in diversity, just like their closest species, and completely dominate the planet for the following ages.
5. The end of the Cretaceous
Finally, 65 million years ago, the famous meteorite impact occurred in the Yucatan Peninsula, Mexico. As if that were not enough, it is assumed that this event triggered intense volcanic activity on the planet.
An increase in carbon dioxide emissions and a drop in oxygen levels in the ocean were followed by rapid post-impact cooling. Around 76% of species and 40% of genera went extinct, ending the reign of the dinosaurs.
After this event, mammals quickly adapted to exploit the newly occupied ecological niches, as did a unique branch of dinosaurs, better known today as birds. It also made possible the advent of mankind.
6. Sixth mass extinction?
Speaking of humanity, human activity could be the catalyst for the sixth mass extinction. A 2015 study in Science Advances estimated that the current rate of species extinction could be up to 100 times higher than the normal rate estimated by geological studies.
The main agents of this increase They are the growth of the human population, the increase in the consumption of resources and the climate change caused by human action. Over time, extinct species reduce biodiversity, destabilize ecosystems and cause more extinctions, creating an ever-growing tide that cannot be easily stopped.
In the end, humanity he may well be not only the agent of the Sixth Extinction, but also one of its victims. Only time will tell if we will survive.