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Sunday, December 26, 2010

Mass extinction of species through ages

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At the end of the International Year of Biodiversity, let us recall the role of nature in extinction. In the current era of extinction of species solely due to human activities, let us say shamelessly, that if nature itself is responsible for greater extinctions, humans should not be cursed for smaller crimes!

The term Mass Extinction refers to any episode of multiple losses of species of plants and animals. However, the term is often used for events of Global Extinction. Global Extinctions have been the disasters when intensive losses of species occurred in all the ecosystems on land and in the sea that affected nearly every part of the earth. Scientists recognize FIVE episodes of mass extinction during the past 500 million years –

First Mass Extinction: It occurred around 438 million years ago in the Ordovician Period during which more than 85 % of species on the earth became extinct. Second Mass Extinction occurred around 367 million years ago near the end of the Devonian period when about 82 % of species became extinct. The Third Mass Extinction occurred around 245 million years ago at the end of the Permian period when about 96 % of species became extinct. The devastation was so great that Paleontologists use this event to mark the end of ancient or the Paleozoic Era and the beginning of the middle or the Mesozoic Era. During this era many new groups of animals and plants evolved on the earth. The Fourth Mass Extinction occurred around 208 million years ago, near the end of the Triassic Period during which about 76 percent species had become extinct from the earth. The populations that had gone extinct during that period mostly belonged to amphibians and reptiles. The Fifth Mass Extinction occurred around 65 million years ago at the end of the Cretaceous Period when about 76 % of the species of the earth including Dinosaurs had gone extinct. It is supposed that this Mass Extinction occurred when one or more big meteorite(s) had struck the earth during the Mesozoic era. This era is also called as the era of reptiles.

Scientists are of the opinion that now the earth is facing the most severe episode of extinction since the extinction of dinosaurs. Biologists say that about 27,000 species are becoming extinct each year, which means: three species per year. The causes of the current mass extinction or the Sixth Mass Extinction are changes in the world climate and anthropogenic pressures. This has come to be known as the 6th mass extinction. The penguin like great auk, the Passenger Pigeon, the Balinese tiger, the quagga, and the moa etc. are the victims of the 6th mass extinction. The passenger pigeon were once abundant in many parts of the world but it became extinct in 1914 as a result of hunting and habitat destruction.

Key words : mass extinction, international year for biodiversity,hunting, habitat destruction

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