Origin

The current Biodiversity, resulting from a long process of evolution initiated some 3-8 billion years ago, arose from primitive forms of life which slowly diversified occupying all the available environments and adapting themselves to the numerous climate changes throughout the eras.
As a consequence of natural disasters or very drastic climate changes, some species have disappeared. Species extinction, which may occur when the given environment where these species live changes drastically, is however a natural, very slow phenomenon counterbalanced by the appearance of new species, better adapted to live in the new conditions.

During the history of life on Earth we can distinguish two main ages, each with an appropriate biology and rhythm: the Pre-Cambrian, the age of the hidden life, a world of microorganisms which colonized the planet during the first 2-5 billion years; and the Phanerozoic, the age of the visible, dominated by small long-lived eucaryotes, which are adapted to live in the various environments formed during the Cambrian (550/600 million years).
The species of the Pre-Cambrian were tiny, asexual and prokaryotes, and the most important evolutionary changes were at the cellular and biochemical level. Massive extinctions were a rare event, concerning especially microalgae eucaryotes or voluminous cells, whereas the Cyanobacteria of the Pre-Cambrian adapted to various conditions because of their evolutionary fitness and longevity.

Plants and animals in the Phanerozoic were on the contrary, big, multicellular and specialized, several species having a relatively brief life. Therefore, the Phanerozoic was characterized by numerous episodes of extinction, but each followed by the success and the diversification of the surviving species through adaptative over millions of years. (Schopf J.W., 2003 dans Dallai R., 2005).

By analyzing the fauna of the past we can however conclude that biodiversity has always been increasing in spite of there having been five massive extinctions throughout the Ages.

In conclusion, there has been in the history of life on Earth an increase of biodiversity, especially as from the Cretacic, when the emerging lands, after their fusion and formation of Pangea and the successive fragmentations, and their subsequent drift to their current position, separated by wide marine basins.

The fauna and flora then evolved in conditions of isolation by generating a high diversity. During the Cenozoic, biodiversity will have reached its maximum, in which the number of marine and land species doubled and tripled, respectively
(Dallai R., 2005).