EXTINCTION EVENTS

A mass extinction event is denoted as such when there is a sharp decrease in the number of species over a relatively short period of time.
Over 97% of species that ever lived on planet Earth are now extinct, with many endangered species today on the brink of extinction. However, todays endangered species are not due to a mass extinction event, but due more to natural selection.

There are five recognised "Big Events", although there could have been others in earlier times when the fossil record was not so complete.
Spanning the last 540 million years they occurred at the end of the Ordovician, the Late Devonian, the end of the Permian, the end of the Triassic, & the end of the Cretaceous.

Ordovician/Silurian Extinction (440m to 450m yrs) - 27% of all families & 57% of all genera died out.

Late Devonian Extinction (360m to 375m yrs) - 70% of all species dissappeared off the face of the Earth. The extinction lasted up to 20m yrs.

Permian/Triassic Extinction (251m yrs) - 90% of all marine species & 70% of all land species died out. A decimation of living creatures.

Trissic/Jurassic Extinction (205m yrs) - 20% of all marine families became extinct, as well as the large amphibians, and therapsids.

Cretaceous Tertiary Extinction K-T (65m yrs) - 75% of living species became extinct. This is probably the best known of all as it ended the regn of the Dinosaurs, and allowed mammalians and birds to become the dominant creatures.

It is considered that the extinctions were due to huge volcanic eruptions, falling sea levels, and asteroid impacts.
All would create huge climatic change, with acid rain, atmospheric dust particles, and in the case of falling sea levels, oversedimentation.
Dust in the atmosphere would inhibit photosynthesis, with the ultimate collapse of the food chain.

Our tenure of this planet is currently very short. The dinosaurs managed 160 million years.
In part, thanks to these Extinction Events, humankind has become the dominant species.

But, for how long !