The Earth stands on the brink of its sixth mass extinction and the fault is ours

The rate at which vertebrate species are dying far exceeds the norm

Life on Earth is in trouble. That much we know. But how bad have things become - and how fast are events moving? How soon, indeed, before the Earth's biological treasures are trashed, in what will be the sixth great mass extinction event? This is what Gerardo Caballos of the National Autonomous University of Mexico and his colleagues have assessed, in a paper that came out on Friday.

These are extraordinarily difficult questions. There are many millions of species, many elusive and rare, and inhabiting remote and dangerous places. There are too few skilled biologists in the field to keep track of them all. Demonstrating beyond reasonable doubt that any single species is extinct is arduous and painstaking (think how long it took to show - to most people, at least - that Loch Ness probably does not harbour a large monster).