In the last 500 million years life has had to recover from five catastrophic blows. More than 99% of all organisms that have ever lived on the Earth are extinct. At least a hadfull of times in the last 500 million years 75 to 90% of all species on Earth have disappeared in a geological blink of an eye in catastrophes we call mass extinctions.
Top 5 worst mass extinction
1. The ordovician-Silurian extinction
439 million years ago
During the ordovician period most life on Earth lived in the sea. A Sudden dropping see levels occurred as glaciers formed and was sudden rise in sea levels occurred as glaciers melted. This dramatically impacted sea dwelling creatures, causing about 25% of marine families and 60% of marine genera to die.
2. The late devonian extinction
364 million years ago
During this extinction event much of the seabed became devoid of oxygen making if inhospitable for anything except bacteria. Scientists think that new plant species caused the climate to change which significantly contributed to the massive loss of life. Notably, the event may have been characterized by a series of extinctions over several million years, rather than a single event. Three quarters of all species died.
3. The Permian-Triassic extinction
251 million years ago
The Permian mass extinction has been nicknamed "The Great Dying," since a staggering 96% of species disappeared. This means that all life on Earth is discended from the 4% of species that survived. Although direct evidence has yet to be found, the primary hypothesis is that an impact event caused dust to cover the Earth, which caused a significant loss of oxygen.
4. The end Triassic extinction
199-214 million years ago
Scientists assert that this event was most likely caused by massive flood of lava eruption from the central Atlantic magmatic province, triggering the breakup of panga and the opening of the Atlantic Ocean. The volcanism may have led to deadly global warming.
5. The creataceous tertiary Extinction
65 million years ago
Also known as the K/T extinction, this is the famed event that led to the death of the dinosaurs. However, many other organisms also perished at the end of the creataceous, including the ammonites, many flowering plants and the last of the pterosaurs. It was caused by the impact of a several kilometer wide asteroids which created the chicxulub creater that is on the Yucatan peninsula and beneath the Gulf of Mexico.
Causes of mass extinction
1. Mass extinction are associated in time with major environmental change.
2. Impact or a series of impacts of extraterrestrial derived objects.
3. Volcanism.
4. Lowering of sea level, which reduces available habitats for marine species.
5. Anoxia, especially transgressive spread of deep anoxic waters on to the continental shelves.
6. Methane hydrates release resulting in extreme global warming.
