Thursday, July 02, 2015
Several times in the history of the earth, "mass global extinctions" have occurred, when virtually all species disappeared. Each such event occurred over a vast spectrum of time, and it then took perhaps millions of years to rediversify. Here is an excerpt and the conclusion to an article which (in full) presents detailed scientific information about what is going on now in our own biosphere that makes it likely that if current trends continue, our planet will undergo mass global extinction within three lifetimes.
"Our results indicate that modern vertebrate extinctions that occurred since 1500 and 1900 AD would have taken several millennia to occur if the background rate [rate of earlier extinctions] had prevailed. The total number of vertebrate species that went extinct in the last century would have taken about 800 to 10,000 years to disappear under the background rate of 2 E/MSY (Fig. 2). The particularly high losses in the last several decades accentuate the increasing severity of the modern extinction crisis."
"The evidence is incontrovertible that recent extinction rates are unprecedented in human history and highly unusual in Earth’s history. Our analysis emphasizes that our global society has started to destroy species of other organisms at an accelerating rate, initiating a mass extinction episode unparalleled for 65 million years. If the currently elevated extinction pace is allowed to continue, humans will soon (in as little as three human lifetimes) be deprived of many biodiversity benefits. On human time scales, this loss would be effectively permanent because in the aftermath of past mass extinctions, the living world took hundreds of thousands to millions of years to rediversify. Avoiding a true sixth mass extinction will require rapid, greatly intensified efforts to conserve already threatened species and to alleviate pressures on their populations—notably habitat loss, overexploitation for economic gain, and climate change (31–33). All of these are related to human population size and growth, which increases consumption (especially among the rich), and economic inequity. However, the window of opportunity is rapidly closing."
(See http://advances.sciencemag.org/content/1/5/e1400253 for the full article, which was then (I believe) reprinted in the Huffington Post)