The history and future of mass extinctions

prehistoric carnivore

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Speciation and extinction are ordinary processes in the natural world. In speciation, new species evolve that are adapted to a particular ecological niche. In extinction, species are lost for good, often because changes in the environment deprive them of the food or habitat to which they are adapted.

Normally the two processes roughly balance each other. But fossil evidence shows that on five occasions, mass extinctions have occurred. They were caused by massive changes in conditions on Earth, like glaciation, widespread volcanic activity, or an asteroid strike. In each mass extinction, more than 75 percent of existing animal species were lost. The most recent one happened 65 million years ago.

Recently, biologists have become concerned that we have entered a Sixth Mass Extinction. Studying both the magnitude and rate of extinctions during the past 500 years, and comparing this information to the paleontological record, they have confirmed that current extinction rates are much higher than in the geologic past. Current extinctions are driven by factors like land development, which leads to habitat destruction, and climate change.

Why should we be concerned? Because ecosystems and their inhabitants make life on earth comfortable for humans. A landscape without bats would be filled with mosquitoes. Without pollinators like bees, our fruit and nut crops would be decimated. Animals of all kinds make our soils fertile.

It is not a stretch to imagine a world so depleted of biodiversity that the very existence of humans would be threatened.



Photo, taken on January 4, 2012, courtesy of Michael Shehan Obeysekera via Flickr.


Earth Wise is a production of WAMC Northeast Public Radio.  Support for Earth Wise comes from the Cary Institute of Ecosystem Studies in Millbrook, NY, with partial support from the Field Day Foundation.


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