Tuesday, December 29, 2015

The Holocene Extinction

Since life evolved and developed, there have been five mass extinctions, the last being about 65 million years ago when a meteorite hit Earth and caused crap to be thrown into the sky that lasted fo years, killing all the dinosaurs. Such mass extinctions have each caused a loss of about 75% of all species.

Earth is now undergoing a sixth mass extinction, one that is known as the Holocene Extinction, this one being due to human impact on the environment. The latter is an aspect of the Anthropocene, or Age of Man. Tthe extinction is also known as the “Anthropocene defaunation.”

Some comments:

· The Holocene Epoch is the current geological epoch that began about 13,700 years ago. It is what gives the extinction event its name,

· Although 875 extinctions occurring between 1500 and 2009 have been documented by the International Union for Conservation of Nature and Natural Resources, the vast majority are undocumented and could be in the many thousands per year when in sects, bugs, plants etc are taken into account.

· The Holocene extinction includes the disappearance of large mammals known as megafauna, starting between 9,000 and 13,000 years ago, the end of the last Ice Age.

· The Holocene extinction continues into the 21st century, with overfishing, ocean acidification and the amphibian crisis (the increasing decline of amphibian populations) being a few broad examples.

· Anthony Barnosky, a palaeobiologist at the University of California, Berkeley, has predicted that if the current rates of extinction continue and the animals already threatened or endangered are wiped out this century, in around 300 years time, 75% of all mammal species will have disappeared from this planet. 

· Barnosky attributes the above to a combination of habitat encroachment and fragmentation, hunting, climate change, pollution, and the spread of disease and introduced species. Whereas extinction is a natural phenomenon that has been balanced by new species evolving, the current, human-caused extinction is happening so fast that evolution cannot keep pace. Barnosky estimates that the current rate is 1,000 times the natural rate, putting it easily on a par with the so-called “big 5” mass extinction events.

· The Age of Man, will be marked by a rapid decline in biodiversity as animals and plants disappear from the planet forever. It won't just be the individual creatures that vanish, but also their descendants on the evolutionary tree. The Anthropocene will also be notable for its homogeneity – what Barnosky describes as the "McDonaldization of nature".

· Not everyone accepts the Holocene extinction. As with climate change, there are those who deny its existence or downgrade the seriousness.

Some extinctions:

The dodo, a flightless bird of Mauritius, became extinct during the mid-late seventeenth century after humans destroyed the forests where the birds made their homes and introduced mammals that ate their eggs.

The quagga, a subspecies of zebra from South Africa, became extinct in 1870.

The Mexican grizzly bear became extinct in 1964.

The Thylacine, or Tasmanian Tiger, became extinct in 1936.

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