Massive extinctions took place millions of years ago, so long ago that life had time to start again from zero, leaving behind creatures that were lost forever in the transformations suffered by a young, inexpert and changing. We are the most efficient agent of a phenomenon which is as old as life itself: the extinction of species. But we are becoming so efficient in our role as destroyers that, as we begin to understand the interdependent mechanisms of life on earth, we are realising that perhaps our own activities could end up leading our species along the road to extinction.
Since the first animal fossil register, approximately 800 million years ago, the Earth has suffered at least twelve massive extinctions, of which five were of truly gigantic proportions.
Millions of species disappeared forever in these periods of massive deaths. When we hear of extinctions in pre-history, we tend to think of the time when the Earth was inhabited by fabulous animals: the dinosaurs.
The dinosaurs dominated the zoology of our planet for one hundred and forty million years, a period which, in comparison with the history of our species, makes them almost eternal.
A medium-sized meteorite crashed into the Earth. It was neither the largest nor the most devastating of the many that have impacted against our planet, but the power of the impact was the equivalent of 10,000 times the detonation of all the nuclear weapons in the world.
Another of the great agents of extinction came with the evolution of the Earth itself.
Since life began, continental drift and fragmentation have brought brutal changes in all land and marine ecosystems. The movement of the tectonic plates changed currents, winds, river courses; it changed the land relief, the coasts, the islands. The structure of the world was radically altered.
Sixty million years ago, the supercontinent Gondwana broke apart, giving rise to new, powerful oceans.
Tectonic movements and the climatic repercussions they bring with them have been responsible for the disappearance of many species. In fact, the first great extinction, 440 million years ago, was due to the southward drift of the supercontinent Gondwana, which gave rise to a prolonged ice age in which around 75% of all the species on the planet were wiped out.
The appearance of man would change the planet forever. Man became sedentary and learnt to cultivate the land from which he would obtain so much food that he could store the surplus for consumption during the unproductive months.
We have become an agent of extinction just as devastating as the drift of continents or the impact of meteorites.The consequences of our actions have become global ecological problems. We are changing the climate of the entire earth and the first signs can be seen where we might least expect it.
We are the cause of the sixth massive extinction, an extinction that is taking place today, right now.
Scientists calculate that in the next one hundred years half of all the living beings on the planet will be in danger of extinction. A ridiculously short period on the scale of extinctions, where time is measured in millions of years.
The Earth has already survived changes similar to those we are bringing about, massive extinctions that led to the disappearance of 95% of all species. It, therefore, will survive all this alarming damage. And life, almost certainly, will return to the Earth. But unless we are capable of avoiding it, our species, like the dinosaurs, the marsupial tigers or the ichthyosauruses, will be merely a memory of an insignificant instant in the long life of the planet Earth.