WHAT IS AN EXTINCTION?

Extinction is the process in which groups of organisms die out. If over an extended period of time the birth rate of a species is less than the death rate, then extinction will eventually occur.

Extinction is a natural phenomenon predicted by Darwin in his theory of evolution.  A species goes extinct if it is not able to adapt to changes in it's environment, or compete effectively with other organisms.

Over the history of the earth over 99% of all the species that have ever lived have gone extinct.

WHAT IS A MASS EXTINCTION? 

Mass extinctions are periodic rises in the extinction rate above the background level. They are events which are not caused by changes in habitat or competition but catastrophes.

Perhaps over 95% of all extinctions have occurred as background events, with the rest consisting of catastrophic events which:- 

• Were geologically rapid ( occurred within a few Million Years) 
• Occurred across the globe
• Had a large number of species going extinct in the same time period
• Spread across all the worlds ecosystems

These are the mass extinctions, they cause a dramatic decrease in the earth's biodiversity, and punctuate the earth's history, and are used by Geologists to break up geological time. Recent thinking has however been to class events by their ecological impacts, rather than by the number of species lost. Click HERE for a brief summary on this topic.

Five main extinction events have been recognized, these are known as the BIG 5.

1.  The late Ordovician event 438 million years ago, when 100 families went extinct
2. Late Devonian 360 million years ago, when 30% of families went extinct
3. End Permian 245 million years ago, the biggest extinction of all time when over 50% of all families were lost.
4. Late Triassic 35% of families died out
5. The Cretaceous  Tertiary (K-T) 65 Million years ago, which ended the reign of the dinosaurs

SEE TIMELINE