What cause MASS EXTINCTIONS???

EXTINCTIONS, The disappearance of a species from the living world, is a natural event. But at five times in Earth's history, at least 50 percent of all species have died out in the mass extinction events. What causes these catastrophes? Are we in the middle of a sixth wave? 

The five great extinctions, in chronological order, were:

Ordovician-silurian (About 440 million years ago): 85 percent of marine species. Cause unknown: possibly the migration of the super-continent Gondwana.  

Late Devonian (359 Mya): 75 percent of species, particularly corals. Cause unknown: possibly a comet or asteroid impact.




Permian (266-251mya): 95 percent of marine species and 70

percent of land species. Causes unknown: possibly impacts from space or volcanic eruptions.







End-Triassic (200 mya): 76 percent of all species . Cause unknown: possibly huge volcanic eruptions.





Cretaceous-Tertiary (65 mya): 80 percent of all species, including

dinosaurs. Cause probably an Asteroid impact.

Most biologist agree that we are now in midst of a sixth great extinction, with a rate up to 80 times higher than normal. If unchecked, 75 percent of earth's species are on track to become extinct within the next 300 years. The cause this time? loss of habitat, pollution, introduction of nonnative species, and climate change are top factors, all linked to human activity.

"At least 50 percent of all species have died out in mass extinction events."



The giant CHELONOIDIS ABINGDONI TORTOISE "Lonesome

George" may have been the last of his kind when he died in 2012.











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