Some science behind the scenes

Mass Extinction

In both biology and ecology, extinction is defined as the cessation on earth of a species or group of taxa. Thus the disappearance of the form on earth.  As most biologists and ecologists have no knowledge of the survival of function, the definition only applies to the decommissioning of form.  The moment of extinction is generally considered to be the death of the last individual of that species (although the capacity to breed and recover may have been lost before this point). 

There have been at least five mass extinctions in the history of life, and four in the last 3.5 billion years in which many species have disappeared in a relatively short period of geological time. The most recent of these, the Cretaceous–Tertiary extinction event 65 million years ago at the end of the Cretaceous period, is best known for having wiped out the non-avian dinosaurs, among many other species.

The classical "Big Five" mass extinctions identified by Jack Sepkoski and David M. Raup in their 1982 paper are widely agreed upon as some of the most significant: End Ordovician, Late Devonian, End Permian, End Triassic, and End Cretaceous.

Timeline of mass extinctions on
Earth within the past 500 million years




According to Wikipedia “ A typical species becomes extinct within 10 million years of its first appearance, although some species, called living fossils, survive virtually unchanged for hundreds of millions of years. Extinction, though, is usually a natural phenomenon; it is estimated that 99.9% of all species that have ever lived are now extinct.

But things have changed…..


Prior to the dispersion of humans across the earth, extinction generally occurred at a continuous low rate, mass extinctions being relatively rare events. Starting approximately 100,000 years ago, and coinciding with an increase in the numbers and range of humans, species extinctions have increased to a rate unprecedented since the Cretaceous–Tertiary extinction event.  This is known as the Holocene extinction event and is at least the sixth such extinction event.

According to a 1998 survey of 400 biologists conducted by New York's American Museum of Natural History, “nearly 70 percent believed the prediction that up to 20 percent of all living populations could become extinct within 30 years (by 2028)”. Biologist E. O. Wilson estimated in 2002 that if current rates of human destruction of the biosphere continue, one-half of all species of life on earth will be extinct in 100 years. More significantly the rate of species extinctions at present is estimated at 100 to 1000 times "background" or average extinction rates in the evolutionary time scale of planet Earth.


For iPad/iPhone users: tap letter twice to get list of items.