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A mass extinction are period on Earth’s history where an abnormally large number of species die out simultaneously or within a limited time period.

Here are the 5 biggest:

Ordovician-Silurian mass extinction:  During this time most life was in the ocean. Sea creatures like the trilobites, brachiopods and graptolites were wiped out. Almost 85% of them were completely gone. What happened was there was an ice age that caused a climate change. Sea levels fell and the chemistry of the ocean was messed up.

Late Devonian mass extinction: This was a series of extinctions over the course of a million years, and not a single event. Life in shallow seas were impacted. Much of the sea bed became devoid of oxygen. Changes in sea level, asteroid impacts climate change have also been blamed for this mass extinction.

Permian mass extinction: This mass extinction has been nicknamed the great dying. A staggering 96% of species have died out. All life on Earth today is the surviving 4%. There were at least two separate phases of extinction spread over millions of years. Marine creatures were particularly badly affected and insects suffered the only mass extinction of their history. Many causes have been proposed for the event: asteroid impact, flood basalt eruptions, catastrophic methane release, a drop in oxygen levels etc. 

Triassic-Jurassic mass extinction: Climate change, flood basalt eruptions and an asteroid impact have all been blamed for loss of life. Many types of animal died out, including lots of marine reptiles, some large amphibians, many reef-building creatures and large numbers of cephalopod molluscs. Roughly half of all the species alive at the time became extinct. Strangely, plants were not so badly affected.

Cretaceous- Tertiary mass extinction: This is famed for the death of the dinosaurs. Many other organisms perished however such as flowering plants & ammonites.This extinction was due to flood basalt eruptions affecting the world’s climate, combined with drastic falls in sea level. Then a huge asteroid or comet struck the seabed near the Yucatan Peninsula in Mexico. 

Many propose that the next big extinction won’t be because of natural disasters but because of man made ones. 

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