The data of geology and paleontology tell us about the existence of about 60 species extinction crises since about 600 million years.
We do not know much about what happened before this period, the species of the time being very little fossilizable (in the absence of external and internal skeletons) and the traces possibly left having disappeared. Geochemistry, however, brings us valuable information, thanks to the world of bacteria and protists .
Since that time, the fossils found are well documented and allow us a more elaborate construction of the “tree of life”. The Earth is dated at 4.6 billion years and the appearance of life on Earth at more than 3.5 billion years . It has appeared in the ancestral ocean , either in the warm, shallow coastal environment or at greater depth around the hydrothermal vents, according to various theories.
Five major crises
Of these 60 crises, five were particularly highlighted by their scale; and they were the subject of a redefinition in an article published by the scientific journal Nature in 2011: these major crises concern the extinction of at least three quarters of living species, marine and continental, on a “short” time.
Immediately, the question arises: what is a “short” time? In geology, it is a time of the order of half a million years. Compared to the situation we have today, time scales are jostling!
Between the geopolitical time of humanity and the time of the Earth, the distances are dizzying. This is why the “Anthropocene era” can not enter the geological scale. It was in 2000 that this notion appeared, proposed by the Dutch Paul Crutzen (Nobel of chemistry in 1995): namely an “era” during which the most powerful factor of changes would be the human species. Crutzen started it with the industrial revolution, at the moment of the invention of the steam engine. Although the idea may seem attractive, it seems more prudent to keep it as an image.
Biodiversity extinction crises have always been multifactorial and have been used for various reasons, which can also often play in common: giant meteorite impact, explosion “close” super nova, brutal warming, collapse of content water and air in oxygen, intense volcanism and gigantic emissions of greenhouse gases, violent earthquakes and tsunamis, encounters of continents, prolonged freezing cold, darkening of the sunlight …
The current crisis
These different characteristics of major extinction crises must be taken into account when talking about the “current biodiversity crisis”. The detailed WWF report of October 2016 set the tone: its “living planet” index indicates a 58% “reduction” overall, for all ecosystems (marine and continental), over a very short period of time. years !
This index is calculated on the collapse of the number of individuals in vertebrate populations (more than 14,000 populations followed for 3,700 species). Some ecosystems are particularly affected, such as freshwater environments (-81%!) Or the Great Plains of Argentina.
It must be emphasized that we are talking about decreases in the number of individuals, not extinctions. They could, of course, happen eventually, but it takes a while. At the scale of a human life, extinctions are rare and linked to endemic species that are very rarely distributed, on islands for example.
The causes of this phenomenon of rapid erosion of biodiversity are well identified: massive destruction of ecosystems, widespread pollution – even in places where humans are not, like the poles) – anarchic spread of species (the “ecological roulette” – a link in this regard), overexploitation of species (fisheries and forests) and, finally, this current climate change much too fast that does not help things .
The loss, degradation and fragmentation of habitats are the main reason. Of course, these losses of biodiversity are very worrying for the services rendered by the ecosystems and many recent works insist on the structuring of the ecosystems to better resist the various current aggressions, triggered by the human activities.
This is the vicious circle in which we are engaged: ecosystems are all degraded and therefore less able to resist. Because of human pressure, in constant acceleration, natural capital decreases faster than it can regenerate. Human activities and the exploitation of resources have developed so much – in connection with the demographic pressure – that the ecological conditions that favored our development and growth are now starting to deteriorate .
The work of the group of researchers led by the Swedish climatologist Johan Rockström has defined planetary limits to our impacts and we announce that out of nine alterations of human origin that affect the Earth system, four have already exceeded thresholds “bearable”; these relate to nitrogen and phosphorus inputs into the biosphere, climate change and the collapse of biodiversity.
And in a much- published article published in May 2017, our Mexican and US colleagues are bouncing back with a long, well-researched study of accelerating biodiversity degradation. They even speak of “biological annihilation”, “defaunation” with catastrophic consequences, based on data from the International Union for the Conservation of Nature (IUCN)relating to 27,600 terrestrial vertebrate species: 32% of them declined in population and distribution.
They were particularly interested in 177 species of terrestrial mammals, showing that 30% of them lost at least 30% of their territory; more than 40% have lost at least 80% of their geographical distribution since 1900! They conclude that the sixth extinction crisis is underway and that the reality still exceeds the most pessimistic forecasts.
We must also mention a very recent study , published on 18 October 2017 in the journal PLoS One , about the decline of flying insects in the last thirty years in Europe.
Reduce our impact
How can the current situation be compared to the crises of the past? The real question can be formulated as follows: how long does it take to return to a state more or less close to the initial one, the one before the crisis?
The triggers of past crises have been analyzed; they are not involved in what is happening today. It is the human activities that are responsible for the present situation. After hundreds of millions of years during which the major factors of the environment – the temperature, the available oxygen, the salinity of the ocean, the composition of the air … – were the driving forces of the evolution of the life and its adaptive capacities, it is the human and its bubbling activities that have become the essential force!
By estimating rates of change, attempting to predict possible trajectories and planning mechanisms, we could undoubtedly greatly reduce our impact on species and ecosystems and thus seriously improve the economic and social costs of our nature activities. .
Also, must we change: we talk a lot about “resilience”, that is to say the capacity for an attacked ecosystem to find a situation of “maintenance of its qualities” more or less close to the stage before the aggression. But do not forget that for an ecosystem to be resilient, it must still not disappear!
He must first resist the aggression then, before risking a complete disappearance, he may be able to enter into resilience, which takes a while. It should also be noted that the situation of “ecosystem changeover” (which refers to the changeover to a totally different state irreversibly), which occurs beyond a certain threshold of disturbance, remains difficult to predict.
Is the state of structuring of our current ecosystems, marine and continental, sufficiently organized to resist? How far can we accept the degradation of species and ecosystems? In addition, it is now shown that abundant and functional biodiversity is generating more biodiversity. This is very important to consider.
It is high time to react and consider as important as accelerated climate change the loss of biodiversity. We consume only organic and cooperate only with organic! So we must admit once and for all our inseparable relationship to life on the planet and to biodiversity: every time we assault, we self-aggressively (and our economy toggle).
For a species that has chosen to be called sapiens , it seems stupid! During this century, let us deserve the term we have conferred on ourselves, we who have not yet passed the stage of Homo faber.