The Earth stands on the brink of its sixth mass extinction

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?

Rather than the nine extinctions among vertebrates that would be expected to have occurred in normal geological circumstances since 1900, their conservative estimate adds in another 468 extinctions, spread among mammals, birds, reptiles, amphibians and fish.


NOT THE FIRST TIME: Previous mass extinctions

Geological history includes many periods when species have died in large numbers. In each of the following, more than half the Earth’s species disappeared:

1 End-Ordovician, 443 million years ago.

This coincides with very rapid glaciation; sea level fell by more than 100 metres, devastating shallow marine ecosystems; less than a million years later, there was a second wave of extinctions as ice melted, sea level rose rapidly, and oceans became oxygen-depleted.

2 Late Devonian, c 360 million years ago.

A messy prolonged event, again hitting life in shallow seas very hard, and an extinction that was probably due to climate change.

3 Permian-Triassic mass extinction, c 250 million years ago.

The greatest of all, ‘The Great Dying’ of more than 95% of species, is strongly linked with massive volcanic eruptions in Siberia that caused, among other effects, a brief savage episode of global warming.

4 Triassic-Jurassic mass extinction, c 200 million years ago.

This has been linked with another huge outburst of volcanism.

5 Cretaceous-Tertiary mass extinction 65 million years ago.

This killed off the dinosaurs and much else; an asteroid impact on Mexico probably did the damage, but the world’s ecosystem may have been weakened by volcanic outbursts in what is now India.

Prof Mark Williams, Leicester University
For more information:
http://www.theguardian.com/environment/2015/jun/21/mass-extinction-science-warning