A N A T U R A L - A N D U N N A T U R A L - P R O C E S S
The world is, and always has been, in a state of flux. Even the land beneath our Feet is constantly on the move. Over hundreds of millions of years, continents have broken apart, oceans appeared, mountains formed and worn inexorably away.
These processes continue, barely discernible over a single human life-time. With geological change come changes in living things: species, populations, and whole lineages disappear, and new ones emerge.
The entire basis of organic evolution is underpinned by the appearance of some species and the disappearance of others; extinction is therefore a natural process
According to the fossil record, no species has yet proved immortal; as few as 2-4% of the species that have ever lived are believed to survive today. The remainders are extinct, the vast majority having disappeared long before the arrival of humans
Extinctions caused by humans are generally considered to be a recent, modern phenomenon. However, humanity's first significant contribution to the rate of global extinction may have occurred during the past 100,000 years, when North and South America and Australia lost 74 to 86% of the genera of "megafauna" - mammals greater than 44 kg
In Australia, where the earliest human remains are dated to approximately 64,000 years, the great majority of the 22 identified genera of large land animals disappeared between 30,000 and 60,000 years ago.
In the Americas, almost 80% of large-bodied genera became extinct. Extraordinary creatures, such as sabre-toothed cats, mammoths, giant armoured glyptodonts and giant ground-sloths, all disappeared some time between 11,000 and 13,000 years ago, coinciding with the dates of the first clear evidence of a human presence there.
Island megafaunas - like giant birds known as moas in New Zealand, the dodo on Mauritius, giant lemurs and the extraordinary elephantbird in Madagascar, or large rodents and ground-sloths in the Caribbean - survived until much more recently than the continental faunas. All seem to have disappeared within a few hundred years after the arrival of humans - in the case of the moas within the last 300 years.
source : http://www.countdown2010.net/documents/Extinction_media_brief_2004.pdf
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