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Monday, April 4th, 2011 . 12:09 pm | No Comments

Are we entering the Earth’s sixth mass extinction?

In the Earth’s past, there have been five mass extinctions, defined as times when 75% of the number of species are lost over a relatively short amount of time.  ANTHONY D. BARNOSKY, professor at the University of California, Berkely, has found in the present case, however, the rate of species loss is faster than it ever has been over evolutionary history, especially if the species currently listed as “threatened” aren’t rescued.

Anthony Barnosky
ANTHONY D. BARNOSKY, source: University of California, Berkely

Mass extinctions for amphibians could take as little as 240 years, 540 years for birds, and 330 years for mammals.  Mass extinctions seem especially hard on larger animals.  There is also the problem of “shifting baselines”, where it depends on what we are comparing present conditions to.  We may consider species richness to be quite normal now, when it is in fact very low, compared to pre-human times, based on the fossil record.

The range of grizzlies has been dramatically shrinking, and they are found in much fewer regions than they were in the past. © Antony D. Barnosky

The Big Five extinctions are characterized by factors such as climate conditions and ecological stressors, which can act together to dramatically worsen the problem.  Ecological stressors today, such as pollution, high carbon dioxide levels, too many humans, habitat loss, and overfishing, are more serious than current species have ever experienced.

If we work intensively now to prevent the extinction of species listed as “critically endangered”, “endangered”, and “vulnerable”, this looming sixth mass extinction event could still be avoided.

For more information, refer to the newscenter of UC, Berkeley or read the abstract of the recent Nature paper.

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