Were There Five Mass Extinctions?

THIS ARTICLE in New Scientist questions whether there were five Mass Extinctions - end of the Ordovician (445 million years ago), the late Devonian (372 million years ago), the end-Permian (252 million years ago), the end-Triassic (201 million years ago) and the end-Cretaceous.

The evidence for mass extinctions is best seen in the marine environment, where fossil preservation is easier. On land preservation is more difficult. And so mass extinction is more difficult to prove. Or is it that mass extinction did not happen on land?

And if it did not happen on land, was it a mass extinction? On land, animals find it easier to move than sea creatures. Plants have seeds which can survive long after the parent dies. Insects, with there rapid regeneration times, seem to avoid extinction. (But have a poor fossil record.)

Much of the argument seems to come down to a matter of definition. Labelling the present day as the Sixth Mass Extinction might make conservation goals more difficult if it comes to arguing about definitions.