A new study has revealed that it took about 10 million years for Earth to recover from the greatest mass extinction of all time.
About 95 % of marine and 70 % of terrestrial life became extinct during what is known as the end-Permian, a time when continents were all one land mass called the supercontinent Pangea. It is currently much debated how life recovered from this cataclysm, whether quickly or slowly.
In the new research by Dr Zhong-Qiang Chen of the China University of Geosciences in Wuhan and Prof Michael Benton from the University of Bristol, the scientists find that recovery from the crisis lasted some 10 million years.
There were apparently two reasons for the delay, the sheer intensity of the crisis, and continuing grim conditions on Earth after the first wave of extinction.
The end-Permian crisis, by far the most dramatic biological crisis to affect life on Earth, was triggered 252 million years ago by a number of physical environmental shocks – global warming, acid rain, ocean acidification and ocean anoxia.
“It is hard to imagine how so much of life could have been killed, but there is no doubt from some of the fantastic rock sections in China and elsewhere round the world that this was the biggest crisis ever faced by life,” Dr Chen said.
Current study shows that the grim conditions continued in bursts for some 5 to 6 million years after the initial crisis, with repeated carbon and oxygen crises, warming and other ill effects.
Some groups of animals on the sea and land did recover quickly and began to rebuild their ecosystems, but they suffered further setbacks. Life had not really recovered in these early phases because permanent ecosystems were not established.
“Life seemed to be getting back to normal when another crisis hit and set it back again,” Prof Benton explained. “The carbon crises were repeated many times, and then finally conditions became normal again after five million years or so.”
Finally, after the environmental crises ceased to be so severe, more complex ecosystems emerged. In the sea, new groups, such as ancestral crabs and lobsters, as well as the first marine reptiles, came on the scene, and they formed the basis of future modern-style ecosystems.
“We often see mass extinctions as entirely negative but in this most devastating case, life did recover, after many millions of years, and new groups emerged. The event had re-set evolution. However, the causes of the killing – global warming, acid rain, ocean acidification – sound eerily familiar to us today. Perhaps we can learn something from these ancient events,” Prof Benton said.