The planet we live on, Earth, is over 4500 billion years old , and after all these years it is not surprising that living beings have had to suffer events in which their life was on the verge of disappearing.
Nature is everything compared to us, and it is nature that, through various events, whether intrinsic to the Earth or devastating astronomical phenomena, is responsible for some of the mass extinctions we know today.
These extinctions, which we will discuss in this publication, are the cause of the death and disappearance of a large number of species , even almost wiping out life on the planet.
In this article, we will begin a journey through history to discover what some of the most remembered mass extinctions were, their causes, and their consequences.
What are mass extinctions?
To begin to understand everything surrounding these events, the first thing we must know is what mass extinctions are.
This phenomenon we're discussing occurs naturally and culminates in the death and disappearance of a large number of species . An extinction is considered mass extinction when at least 10% of species disappear within a year or when more than 50% disappear over a period of one to three million years.
Many professionals in the sector warn that we may be on the verge of a new extinction, since it is we human beings who are causing damage to the survival of other living beings.
The damage we're talking about can be seen in the horrific environmental impact we're causing . But it takes even more devastating forces of nature to reach the point of a mass extinction.
According to many studies on life on Earth, there have been at least five periods of mass extinctions throughout one of the four eons into which the planet's life is divided, the Phanerozoic Eon.
Each of these five mass extinctions occurred at a specific point in Earth's history . The causes, the degree of devastation, and the subsequent consequences were different in each case.
What are the five great mass extinctions?
When we are clear about what mass extinctions consist of, we are going to address what were the mass extinctions that have occurred throughout history.
Ordovician – Silurian
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We are talking about the first recorded mass extinction ; we have to go back to the Ordovician Period more than 480 million years ago.
During this historical period on planet Earth, life existed only in the sea ; all complex organisms lived in that environment. This life was limited to beings such as bivalve mollusks, cephalopods, graptolites, brachiopods, bryozoans, and others.
The exact cause of this mass extinction is unknown , but the most widely accepted theory is that a gamma ray struck the Earth's atmospheric layer, destroying it and allowing ultraviolet rays to penetrate without any barrier.
This led to the disappearance of plankton, phytoplankton, and some of the organisms that lived within them due to food scarcity. The death of eggs and larvae from ultraviolet radiation and warming also contributed to the problem. All of this caused ocean currents to stagnate, preventing nutrients from being distributed throughout the sea and reaching other living organisms.
After all this, there was a major glaciation . This first extinction event was caused by a gamma-ray burst at the beginning of an ice age. It affected many of the areas where most of the organisms mentioned earlier lived.
The glaciation arose from tectonic plate movements that caused the supercontinent Gondwana to drift towards the South Pole . This led to the formation of countless glaciers on the Earth's surface, causing ocean levels to drop as vast quantities of water solidified.
Ocean currents underwent significant changes , affecting oxygen levels in the seas and the circulation of food. This led to the rapid disappearance of many species.
The few species that managed to survive had to adapt to new conditions, but later, they suffered a second mass extinction at the end of the ice age we are talking about.
The supercontinent once again shifted southward, causing glaciers to melt and sea levels to rise . These changes in the sea led to the death and extinction of 85% of species.
Devonian–Carboniferous
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Following the mass extinction of the previous period, life managed to recover and be reborn; first plants emerged, and later arthropods. This period began approximately 419 million years ago, after the Silurian period.
This second mass extinction mainly affected marine species, reefs, and other living organisms that lived in the aquatic environment, such as fish, cephalopods, sponges, etc.
The global cooling theory is the most widely accepted by experts to explain the causes of this extinction. Ocean waters cooled, causing approximately 82% of the species that existed at that time to disappear over a period of 3 million years.
Permian–Triassic
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Approximately 250 million years ago, hostile conditions on Earth led to the worst mass extinction known to date. Experts estimate that around 95% of marine species and 75% of terrestrial life became extinct.
During this period, land areas began to grow, expand, and diversify. Geologists suspect that this mass extinction was caused by intense volcanic activity and the subsequent release of methane into the sea.
Over the years, and with the help of fossil remains, a group of researchers has reconstructed the events and it appears that it wasn't methane emissions that caused this disaster, but rather large magma emissions . This led to global warming and a chain of catastrophes that turned the planet into a desert.
This achievement of events that occurred over a million years explains why about 95% of the species that inhabited the Earth disappeared.
Triassic – Jurassic
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As has happened after a great mass extinction, life clung on and recovered as best it could. This fourth extinction occurred about 200 million years ago at the end of the Triassic Period and marked the beginning of the Jurassic Period.
During this period, different mammals and dinosaurs were allowed to thrive and establish themselves as the dominant species on the planet at that time.
The lives of these marvelous beings would end with a fourth mass extinction . Pangaea was already a single supercontinent, but it began to fragment and divide into the continents we know today.
This process caused climate change which, combined with intense volcanic activity and meteorite impacts , led to the extinction of many species. Several different hypotheses exist about what actually caused this extinction, and they all ultimately conclude that it was a series of events.
Nearly 76% of the species of living beings that inhabited the earth disappeared over the course of a million years.
Cretaceous – Tertiary
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It is also known as the Cretaceous-Paleogene period and was a time of mass extinctions that occurred approximately 66 million years ago. During this stage of Earth's history, the great dinosaurs emerged , becoming the undisputed rulers of the planet.
As we have discussed, approximately 66 million years ago, a large meteorite impacted the Earth, and from there a new extinction began in history.
This extinction event was responsible for the disappearance of numerous species from Earth and all the dinosaurs . The exact duration of this extinction is unknown, but the devastating consequences of the meteorite impact are well documented.
One of the most negative consequences was that this impact created a dust cloud that settled in the atmosphere. This prevented sunlight from penetrating, thus hindering plant growth and preventing photosynthesis. Furthermore, CO2 and oxygen levels were disrupted.
All of this triggered a series of negative consequences for the species that managed to survive. Herbivores had no plants to eat, and carnivores had no food either. So, practically no living thing on land managed to survive.
As we have been able to verify in each of these 5 periods of mass extinctions, the living beings that inhabited the earth were very fragile. But life managed to recompose itself and period after period arose from nothing and managed to create new species.