E. Ancient extinctions and biodiversity
Biological diversity has not remained unaltered since life began on Earth over three billion years ago. The fossil record is incomplete, both in the time sequences as well as with types of organisms represented in it, but paleontologists generally accept that present times constitute the climax of the species richness of the planet. During the Cambrian Epoch they had the highest taxonomic levels in phyla - much higher than at present.
Five major extinction events have taken place in the last 600 million years. The most severe of them required some 100 million years for recovery. In stark contrast to those figures generated by natural causes, we are facing the gestation of a new extinction event due to humankind's economic activities that will turn out to be the most severe in the history of life on Earth. Even within the context of rather crude estimations of our absolute biological diversity, most biologists agree that rates of species loss due to human activity are several orders of magnitude faster than rates of production of new species, a process which is a fair amount.
Habitats all over the world are under threat. Almost all will suffer severe consequences for organisms living in them. Populations of species are diminishing or disappearing locally causing, in the end, the global extinction of an increasing number of groups. The invasive species, both introduced and opportunistic, become ever more common as a result of these changes.