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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What's the secret behind TREES' LONGEVITY

The Llangernyw yew, spreading it's branches over a graveyard in Wales, saw Britain's Bronze Age. The Bristlecone pine known as Methuselah, in Califonia's Inyo Forest, is even older at 4,765 years, possibly the world's oldest individual tree. 

The Pando aspen colony in Utah makes them look like springs, however . Considered a single living organism, because its genetically identical stems spring from a single root system, the aspen colony is at least 80,000 years old. By some estimates, it may be as much as one million years old.

How do trees defy the aging process that all life should be heir to? According to scientists, they have advantages the human body lacks. Their genes don't seem to mutate or become damaged over timer, they retain stem cell-like cells with each growth cycle; their vascular system allow a portion of the tree to survive if another part dies; they can replace damaged organs; and some can form clones, as in the case of the Pando

Aspens. Why can't researchers be definite about the Pando Aspens colony's age? Lacking tree rings, observers make estimates based upon what they know of aspen growth rates. Other, older aspens colonies may yet be found in western United States. Scientists are also learning to regenerate ancient plants- in 2012, a Russian team reported that it had grown a delicate Siberian Flower from 32,000 years-old seeds.

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