Life has evolved over billions of years, creating an incredible variety of increasingly diverse and complex life forms. It is estimated that the number of species currently inhabiting the Earth could be on the order of 8.7 million.
Biodiversity is not evenly distributed over the surface of the planet. It will not go unnoticed that rainforests or coral reefs contain a greater number of species than sandy deserts or deep ocean abyssal plains.
It is also not surprising that it is said that the most diverse ecosystems are, in part, because they have a greater quantity of resources (water, electricity, food, etc.). Resources are essential, but at the same time limited. For this reason, scientists have debated for decades whether or not there is an equilibrium level above which the number of species cannot continue to grow. In other words, is there a maximum number of species the Earth can support? And, if it exists, has it already been made?
The balance of biodiversity
The concept of balance has its analogy in many areas of science and society. Market equilibrium, for example, a concept widely used in economics, occurs when supply and demand tend to equalize. The increase in supply drives prices down. Falling prices trigger demand. The increase in demand again increases prices and so on, giving rise to a feedback system that keeps the market in equilibrium.
Suppose for a moment that the surface of the Earth is a closed system, that is to say that there has been no exchange of matter and energy between the surface of the planet, its interior and exterior space. If so, one would expect biodiversity to have increased over time until it reached the equilibrium level. The question is: were 3.8 billion years enough to achieve this balance?
Answering this question requires reconsidering the assumption that the Earth’s surface is a closed system. It is not, and as such has suffered environmental disturbances that have caused the extinction in a relatively short time of at least half of the species that inhabited the planet.
The five great mass extinctions
To our knowledge, the increase in volcanic activity, resulting from the radioactive energy accumulated inside the Earth, and the impact of extraterrestrial bodies were the main triggers of the mass extinctions. In both cases, these disturbances have led to changes in climate, increases in the atmospheric concentration of lethal gases, ocean acidification and widespread anoxia, variations in sea level or long periods of planetary darkness that have interrupted vital activity and accelerated the extinction of species.
Of the five major mass extinctions that occurred in the Phanerozoic, that is, during the last 541 million years of Earth’s history, the one that occurred at the end of the Permian, there about 250 million years ago, was the deadliest. everything. This mass extinction event wiped out over 90% of the planet’s species, leaving ecosystems on the brink of collapse.
Today, 250 million years later, Earth’s biodiversity is greater than it has ever been.
The most diverse world
In a recent study published in the journal Naturewe show how the frequency of mass extinction events that took place in the Paleozoic (between 541 and 252 million years ago) prevented marine ecosystems from reaching the balance of diversity.
In contrast, the environmental stability that followed the Paleozoic era allowed the formation of biodiversity hotspots; regions characterized by the fact that they harbor extraordinarily diverse biological communities. These regions, found today in the shallow seas of Indonesia, the Caribbean and Madagascar, may have reached a peak of diversity for the first time in the history of life.
Towards the sixth great extinction
Since the Industrial Revolution, the burning of fossil fuels has transferred large amounts of carbon from the geological reservoir to the atmosphere and oceans. This disturbance, caused by man, alters the natural functioning of ecosystems. The sixth great mass extinction is already underway.
According to the United Nations, over the past century as many species have disappeared as there would have been in 10,000 years in a normal scenario. In addition, 25% of the species assessed by the International Union for Conservation of Nature They are now in danger of extinction.
Biodiversity hotspots are particularly vulnerable regions and their conservation must therefore be a priority. Preventing its deterioration is the best way to stop the accelerating extinction of species, each of which has millions of years of evolutionary success. A treasure, biodiversity, which, if current trends continue, will take millions of years to recover. Most likely beyond our own existence as a species.