In the last 500 million years, life has been on the brink of extinction five times. A journey through history analyzing the causes and consequences of the great mass extinctions.
Life is very fragile . And it is that both ourselves and the rest of living beings do not cease to be, despite the biological miracle that our existence represents, pieces of organic matter that inhabit a world full of geological and even astronomical dangers.
Therefore, it is not surprising that since the appearance of life on Earth some 3,500 million years ago, living beings have had to experience events that put them on the verge of disappearance. No matter how adapted we are to our world, we are nothing compared to the power of nature.
And this nature, both due to intrinsic events on Earth and devastating astronomical phenomena, has been responsible for at least five major mass extinctions. These extinctions were responsible for the death of millions of species and some even came close to making life disappear from the face of the Earth.
In today’s article, then, we will embark on a journey through history, going back some 500 million years, to discover the causes and consequences of the five great mass extinctions , events that, in part, made it possible for you to be today here reading these lines.
What is a mass extinction?
A mass extinction is a natural phenomenon whose development culminates in the disappearance of a significant number of species. In general terms, to speak of mass extinction, this disappearance must be of at least 10% of species over the course of a year or of more than 50% of species over a period of time between one and three and a half million years .
There is talk that we are currently at the gates of a sixth mass extinction. And this, despite the fact that it is totally true that human activity is wreaking havoc on the survival of other species (according to the UN, 150 species disappear every day), it continues to generate controversy within the scientific community.
And is that, really human beings are so powerful as to cause a mass extinction? The answer, surely, is no. The environmental impact of human activity is horrible, without a doubt, but to face a mass extinction, only the most devastating forces of nature can be the protagonists.
Meteorite impacts, climatic changes, rise and fall of the oceans, massive volcanic eruptions and even stellar explosions of stars located thousands of light years away in the form of a supernova.
Throughout the Phanerozoic Eon (one of the four eons in which the history of the Earth is divided from 541 million years in the past to the present) and according to what we have been able to rescue from the geological and biological history of the Earth , life has passed, as far as we know, through at least five periods of mass extinction .
Each of them took place at a specific moment in history, had specific causes, had a specific level of devastation and had specific consequences. So let’s start our exciting journey.
What have been the great mass extinctions?
Once we understand what a mass extinction is, we can now begin our journey through history to find them. The first great mass extinction took place about 445 million years ago, when life was still limited to the sea. And the last one, probably the most famous (but also the least devastating), was the one that happened 66 million years ago and that put an end to the age of the dinosaurs. Do you want to know the secrets of all? Let’s go there. We will indicate to the side the percentage of species that disappeared .
Ordovician-Silurian extinction: 85%
The first mass extinction on record. We have to go back to the Ordovician Period, an age of the Earth that began 485 million years ago and ended with this extinction. But let’s not get ahead of ourselves.
At this time, life only existed in the sea and was limited to brachiopods, bryozoans, trilobites, conodints, graptolites, bivalve molluscs, cephalopods, the first vertebrate fish, etc. Life was proliferating enormously. But nature showed him, for the first time, its strength.
But what happened? What was it that caused it? Well, there is no record of any meteorite impact or intense volcanic activity, but there is evidence of an ice age. This is the most accepted theory. Some say that it was caused by the arrival of gamma rays from a supernova on Earth, but this theory has few defenders.
This glaciation, surely, arose from the movements of the tectonic plates, which dragged the Gondwana supercontinent to the South Pole. This caused countless glaciers to form on the earth’s surface (where there was no life yet) and, therefore, as so much water solidified, the levels of liquid water in the oceans decreased.
This caused enormous changes in the marine currents, in the circulation of nutrients and in the oxygenation of the oceans. Species began to disappear out of control. And those that survived had to face a new extinction (this first mass extinction is the sum of two extinctions) caused by the displacement of the supercontinent towards areas of Ecuador, which caused the deglaciation of the glaciers and a new rise in the level of the sea.
These fluctuations in sea level caused that, in a period between 500,000 and 1 million years, 85% of the species of living beings disappeared , which makes this mass extinction the second most devastating in history. With it the Ordovician Period ends and the Silurian begins, hence its name.
Devonian-Carboniferous extinction: 82%
After this first mass extinction, the survivors (only 15% of the species that inhabited the Earth) proliferated and allowed life to make its way. The Devonian Period began 419 million years ago (after the Silurian) and it was in this age that life arrived on land. First the plants and then the arthropods.
But in the midst of this age of biological explosion, the second big bump for life took place. 359 million years ago, the second great mass extinction in the history of the Earth occurred, which mainly affected marine species (like the first), being especially devastating for reefs and many other animals (fish, trilobites, cephalopods, sponges, etc.). brachiopods, foraminifera…) that inhabited the oceans, especially the most temperate ones.
It is not very clear what geological event drove this great extinction, but there are different theories. That of global cooling is the most accepted. And it is that a proliferation of organisms adapted to low temperatures is observed, the oxygen data reveal that the temperatures at that time decreased, there are changes in the carbon cycle… But there are also indications of intense volcanic activity and even meteorite impact , although these do not coincide exactly with the time of extinction.
Be that as it may, this second mass extinction, surely caused by a cooling of the waters of the oceans, was responsible for, in the course of three million years, the disappearance of 82% of the species of living beings, which makes it the third most devastating. It marks the border between the Devonian and Carboniferous Periods.
Permian-Triassic extinction: 96%
The most devastating extinction in Earth’s history took place 250 million years ago. Life was about to disappear. And it is that only 3% of the species that inhabited the planet survived it. After the second mass extinction, life proliferated a lot.
In fact, it was in the Permian Period (after the Carboniferous) that life on land began to grow, expand and diversify. The great amphibians arose and the reptiles appeared. Land animals colonized the world and marine animals continued to expand.
But 250 million years ago, the greatest mass extinction in history took place, which is known as “The Great Dying” . His name says it all. Therefore, devastating climatic phenomena had to occur.
Although the causes are not completely clear, we have evidence that a massive meteorite hit Antarctica at that time, that intense volcanic activity took place and that large amounts of hydrogen sulfide, a highly toxic substance, were emitted into the sea.
These three events, together, explain why, in the course of 1 million years, 96% of the species on Earth disappeared , being especially devastating in the living beings of the oceans. Life was about to be completely exterminated. This extinction ends the Paleozoic Era and marks the beginning of the Mesozoic.
Triassic-Jurassic Extinction: 76%
Following this devastating Permian extinction, life recovered and continued to proliferate . In fact, mass extinctions are actually an opportunity for the survivors to shape the biological future of the Earth.
It was precisely in the Triassic Period, which began 251 million years ago, that both mammals and dinosaurs emerged, which began to establish themselves as the dominant animals on Earth. At the same time, Pangea already formed a single supercontinent.
But this golden age for life would end with the fourth mass extinction. About 200 million years ago, Pangea began to fragment and break up into the current continents. This caused enormous climatic changes that, together with an age of intense volcanic activity added to the impact of meteorites, caused the disappearance of an enormous number of species.
In the course of 1 million years, 76% of the species of living beings disappeared, affecting both terrestrial and aquatic organisms. Therefore, the fragmentation of Pangea, the volcanism and the impact of meteorites promoted the fourth great mass extinction , the one that would mark the end of the Triassic Period and the beginning of the Jurassic.
Cretaceous-Tertiary extinction: 75%
After the fourth extinction, life proliferated like never before. The great dinosaurs arose and became the undisputed kings of the Earth. The Cretaceous began 145 million years ago (after the Jurassic) and represented an age of enormous biological diversification.
But all kingdoms have an end. And the dinosaurs were not going to be an exception. 66 million years ago, a 12 km diameter meteor impacted what would now be the Gulf of Mexico. And from here, the rest is history.
This meteorite impact caused the fifth mass extinction in history, responsible for the disappearance of 75% of species on Earth and the total annihilation of the dinosaurs. But without them, mammals had a chance to proliferate. That we are here today is, without a doubt, thanks to the impact of this meteorite. If it had passed by, who knows what life would be like today?
Be that as it may, it is not known exactly how long the extinction lasted, but we do know that the consequences of the impact were devastating. The Earth was covered by a cloud of dust that remained in the atmosphere for 18 months and that prevented plants from having sunlight to photosynthesize.
And from here, the food chain collapsed (besides the amounts of carbon dioxide and oxygen were altered). The herbivores had no plants to feed on, so they died. And the carnivores, the same. Virtually no large land animals survived.
Not to mention that the average temperature of the Earth could increase by up to 14 °C, which caused the sea level (due to the melting of the glaciers) to rise more than 300 meters, which not only altered the ocean currents and the circulation of nutrients (greatly damaging sea life), but left much of the continents inundated.
We began the article by saying that life was very fragile. And now, coming to the end, perhaps we should modify this statement. It is living beings that are fragile. Not life. No matter what happens. She always finds a way .