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Earth may be on the brink of a sixth mass extinction on the scale of the apocalyptic event that wiped out the dinosaurs, a study claims.
The researchers say that unless action is taken now to reverse the harmful effects of human activity on eco-systems, a full-blown mass extinction could occur within a few centuries.
Recovery from such an event, which could eradicate more than three-quarters of all life on Earth, may then take millions of years.
Only five previous mass extinctions have occurred in the last 540million years.
They are classified as the Ordovician event (443million years ago); the Devonian event (359million years ago); the Permian event (251million years ago); the Triassic event (200million years ago) and the Cretaceous event (65million years ago).
The last mass extinction, thought to have been triggered by a meteor impact in Mexico, was marked by the loss of 76 per cent of species including the dinosaurs.