Earth may be in the midst of the greatest extinction ever, according to a new mass extinction scoring system.

"The current extinction resembles none of the earlier ones, and may end up being the greatest of all," write Istanbul Technical University researchers A. M. Celal Sengor, Saniye Atayman and Sinan Ozeren.

Their system, published today in the Proceedings of the National Academy of Sciences, attempts to quantify those periods when more than half of all species disappeared. In addition to the current mass extinction, this has happened at least five times: the End Ordovician, Late Devonian, End Permian, End Triassic and End Cretaceous. The latter – marking the end of the Age of Dinosaurs – receives the most attention, but scientists have been unable to decide which extinction was most significant.

That debate may finally be settled, though the answer is unsettling.

"If unchecked, the current extinction threatens to be the greatest killer of all time," write the researchers.

By multiplying the number of organismal groups that went extinct with the time it took, they arrived at a metric called

"greatness." According to this, the dinosaur-ending End Cretaceous event, possibly caused when asteroid strikes or volcanic explosions sheathed the Earth in ash, was twice as great as any previous extinction.

The Permian extinction event, caused 250 million years ago by the formation of the Pangea supercontinent and volcano-induced oceanic poisoning, placed third on the researchers' rankings – and it still encompassed the loss of 96 percent of Earthly life.

According to the researchers, the current global die-off combines elements of both the End Cretaceous and the Permian.

The global dominance of humans "represents a virtual Pangea formation,"

and human activities are a "global annihilating agent" comparable to any asteroid.

The International Union for the Conservation of Nature estimates that 800 plant and animal species have gone extinct in the last 500 years, with more than 16,000 currently threatened with extinction – and those lost or threatened organisms come the from mere 41,000 species so far assessed by science. More than a million have been described but remain unstudied.

The most troubling figures, however, come not from the total species lost but the rate at which they're vanishing: 1,000 times faster than usual. But even that alarming rate may be too conservative. According to a paper recently published in Nature, modeling errors led scientists to grossly underestimate the survival chances of threatened species.

"The older models could be severely overestimating the time to extinction," said University of Colorado ecologist and Nature study co-author Brett Melbourne to the Guardian. "Some species could go extinct 100 times sooner than we expect."

A scale of greatness and causal classification of mass extinctions: Implications for mechanisms [PNAS] [not yet online]

Image: Blu

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