Life on Earth is hurtling towards extinction levels comparable to those following the dinosaur-erasing asteroid impact of 65 million years ago, propelled forward by human activities.
Scientists from the University of California, Berkeley, believe that if current extinction rates continue unabated, and vulnerable species disappear, Earth could lose three-quarters of its species as soon as three centuries from now.
''That's a geological eyeblink,'' said Nicholas Matzke, a graduate student at UC Berkeley and author of a paper presenting the doom-and-gloom scenario. ''Once you lose species, you don't get them back. It takes millions of years to rebound from a mass extinction event.''
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This means that not too far in the future, backyards might not be buzzing with bees, bombarded by seagulls or shaded by redwood trees. And while that might seem far off, species already are disappearing on a global scale.
In recent history, we've lost the dodo bird and the passenger pigeon, the Javan tiger and the Japanese sea lion. Amphibians, mammals, plants, fish - none are immune to going the way of the dinosaurs, courtesy of the human impact on fragile ecosystems.
Such enormous losses have occurred only five times in the past half-billion years, during events known as ''mass extinctions''. The best-known of these occurred 65 million years ago, when an asteroid collided with Earth, sending fiery dust into the atmosphere and rapidly cooling the planet.
These ''Big Five'' events set the extinction bar high: to reach mass wipe-out status, 75 per cent of all species need to disappear within a geologically short time frame, meaning that Earth is currently on the brink of the sixth mass extinction.
To determine whether current losses could equal these mass extinction rates, scientists compared recent rates with species die-offs during the Big Five, taking into account currently endangered species.
They found that while rates are dramatically higher than expected, the percentage of vanishing species is not elevated - yet.
''The good news is, we still have most of what we want to save,'' said Berkeley palaeontologist and lead study author Anthony Barnosky. ''But things are clearly going extinct too fast today.''
The paper, published in this week's issue of Nature, resulted from a graduate seminar that Professor Barnosky organised in autumn 2009.
Focusing on our milk-bearing relatives, mammals, he and students used fossils to compare extinction rates with more modern data, wanting to answer whether we really are seeing the sixth mass extinction.
Stanford University biologist Paul Ehrlich, who was not involved in the study, said evidence of the sixth extinction is all around. For years, he studied the Bay Checkerspot butterfly on Stanford's campus - but then, more than a decade ago, the butterfly disappeared from the campus.
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Posted by Dinosaurs World at 9:58 PM