Species diversity, also referred to as biodiversity, is an essential part of proper ecosystem structure and functioning and ecosystem services.
Speciation, the formation of new species, and extinction, the permanent loss of species, are the major components of changes in the earth's biological diversity.
Over the entire period of life on earth, a few billion years, some plant and animal species have disappeared and new species have appeared as a result of natural evolutionary processes.
The background rate of extinction (or normal extinction rate) is a measure of the rate of species disappearance due to natural processes operating under normal conditions.
The rate has been determined to approximately five extinctions per year on average over geological time. Much greater rates of extinction have occurred during specific periods in earth's history.
These events, called mass extinctions, took place approximately 440, 360, 250, 200, and 65 million years ago. The causes of these extinction events were natural factors such as volcanic eruptions and asteroid impacts.
These natural processes produced major changes in climate and habitats to which many species could not adequately adapt. These events are estimated to have caused the extinction of 50 to 96 % of species present at each time.
The current extinction rate is estimated to be anywhere from 10 to 1000 times the background rate of extinction, with the rate varying across taxonomic groups.
This is the result of a myriad of human activities and their impacts over and above natural factors. The current climate change scenario is changing and accelerating the rate of species extinction by reducing the time plants and animals have to adapt to changes in ecosystem conditions.
Further complicating this issue is the fact that biodiversity is unevenly distributed across the planet, where more than 1/3 of the known land plants and vertebrates confined to 2% of the planet surface, the so called, biodiversity hotspots.
Dinosaurs disappeared from the planet Earth during the mass extinction event of:
