http://en.wikipedia.org/wiki/Holocene_extinction_eventThe Holocene extinction event is a name customarily given to the widespread, ongoing mass extinction of species during the modern Holocene epoch. The large number of extinctions span numerous families of plants and animals including mammals, birds, amphibians, reptiles and arthropods; a sizeable fraction of these extinctions are occurring in the rainforests. Because the rate of this extinction event appears to be much more rapid than the "Big Five" mass extinctions, it is also known as the Sixth Extinction. Since 1500 AD, 784 extinctions have been documented by the International Union for Conservation of Nature and Natural Resources<1>. However, since most extinctions are likely to go undocumented, scientists estimate that during the last century, between 20,000 and two million species have become extinct, but the precise total cannot be determined more accurately within the limits of present knowledge. Up to 140,000 species per year (based on Species-area theory)<2> may be the present rate of extinction based upon upper bound estimating.
In broad usage, the Holocene extinction event includes the notable disappearance of large mammals, known as megafauna, by the end of the last ice age 9,000 to 13,000 years ago. Such disappearances have been considered as either a response to climate change, a result of the proliferation of modern humans, or both. These extinctions, occurring near the Pleistocene / Holocene boundary, are sometimes referred to as the Pleistocene Extinction Event or Ice Age extinction event. However the Holocene extinction event continues through the events of the past several millennia and includes the present time.
The observed rate of extinction has accelerated dramatically in the last 50 years, to a pace greater than the rate seen during the Big Five. There is no general agreement on whether to consider more recent extinctions as a distinct event or merely part of a single escalating process. Only during these most recent parts of the extinction have plants also suffered large losses. Overall, the Holocene extinction event is most significantly characterised by the presence of man-made driving factors and its very short geological timescale (tens to thousands of years) compared to most other extinction events.