The starter: an introduction to the mass extinction

What is a mass extinction? 

The definition should include three parts as following:

1. It  must be an event happening within a geologically short time period (usually varies from a few hundred thousand to a couple million years).

2. In this period, a significant part (above 75%) of all life on earth became extinct.

3. The extinct life forms should have belonged to different phyla and lived in different places with different habitats in the whole world.

In the year 1982, Jack Sepkoski and David M. Raup identified the world had suffered five major mass extinctions (can be named as "big five") in the past 540 million years in a landmark paper.

(The graph above shows the timeline and the highlighting points are the major mass extinctions)

The "big five" events:

1. Ordovician-Silurian extinction event

450 to 440 million years ago which killed about 27% of all families and 57% of all genera.

2. Late Devonian extinction event

375 to 360 million years ago. 19% of all families, 50% of all genera and 70% of all species on earth became extinct.

3. Permian-Triassic mass extinction event 

251 million years ago. Only 4% of species survived on Earth.

4. Triassic-Jurassic mass extinction event

205 million years ago. 23% of all families and 48% of all genera died out. 

5. Cretaceous-Paleogene extinction event 

65.5 million years. 17% of families, 50% of all genera and three quarters of all species went extinct. 

(The figure shows the time and types of species went extinct in those major mass extinction events)

I will then introduce those big five mass extinction events in details and analyze what are the causes of mass extinctions in this blog. After that, based on the research of this area, I will develop whether our Earth will suffer the six mass extinction and whether the anthporocene will accelerate the event.

Reference:

http://mindblowingscience.com/science-by-numbers/the-5-major-mass-extinction-events/

http://www.bbc.co.uk/nature/extinction_events