What is know, however, is that this mass extinction killed 22 percent of marine families and 57 percent of marine genera. Scientists have also suggested that meteorite impacts may have been possible agents for the Devonian mass extinction, but the data in support of a possible extra-terrestrial impact remains inconclusive, and the mechanisms responsible for the Devonian mass extinction are still under debate. Similarly to the late Ordovician crisis, agents such as global cooling and widespread lowering of sea-level may have triggered the late Devonian crisis. Thus this theory suggests that the extinction of the Devonian was triggered by another glaciation event on Gondwana, which is evidenced by glacial deposits of this age in northern Brazil. However, evidence supporting the Devonian mass extinction suggesting that warm water marine species were the most severely affected in this extinction event, has lead many paleontologists to believe that an episode of global cooling, similar to the event which that may have resulted in the Ordovician-Silurian mass extinction, may have lead to the Devonian extinction. T he Late Devonian extinction took place somewhere around 364 million years ago. During this extinction 25 percent of marine families and 60 percent of marine genera (the classification above species) were lost. T he Ordovician-Silurian extinction occurred about 439 million years ago due to a drop in sea levels as glaciers formed followed by rising sea levels as glaciers melted. Many species vanished in five cataclysmic mass extinctions and today, 99.9 percent of all species that have existed on Earth are extinct. These extinctions are quite different from the rate of extinction, which occurs even when the diversity of life is increasing. Time periods in the history of life on Earth during which exceptionally large numbers of species go extinct are called mass extinctions. Rediscovered Species Why Save Endangered Species? Extinct Species Extinct Species Charts Overall Extinct Species List Detailed List of Recent Extinct Species Threatened Species
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