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Friday, 17 July 2015

Measuring the sixth mass extinction


The Earth teeters on the edge of a sixth mass extinction – or so a recent study published in Science Advances has claimed.

Gerardo Ceballos from the National Autonomous University of Mexico and his colleagues calculated that by land clearing, hunting, introducing pests and burning fossil fuels humans have driven the extinction rate to 100 times the rate they believe it would be otherwise. And that’s a conservative estimate, they add.

But measuring extinction rates is not straightforward. The study only counted vertebrates – ignoring creatures such as the insects, spiders and crustaceans that make up 80% of the world’s animal species, not to mention plants, fungi and microbes.

No rule defines what constitutes a mass extinction. “The Earth’s history is punctuated with these extinction events, and we’ve known about them since the 1800s,” says Jessica Whiteside, a palaeobiologist at the University of Southampton in the UK. “But a ‘mass extinction’ is a loose term.

It’s generally defined as a loss of more than one major group of species, across marine and terrestrial environments, tied to a trigger like climate change.” All scientists do agree, though, that a mass extinction is an event where the extinction rate is much higher than the rate at which species die out naturally. 

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