Anoxic Waters Delay the Recovery of Life on Earth by 5 Million Years After the Mass Extinction

A new study revealed that oxygen-starved oceans, or a condition known as anoxia, delayed the recovery of life on Earth by five million years after the Permian-Triassic Boundary extinction 252 million years ago.

The Permian-Triassic Boundary extinction is the greatest mass extinction event of all time, wiping out 90 percent of marine life and two thirds of the animals living on land.

Previous study suggests that the delayed recovery of Earth was caused by the presence of anoxic waters that also contains high levels of harmful compounds known as sulphides. However, a new study published in the journal Nature Communication showed that iron-rich, low oxygen water is the major cause of the delayed recovery of marine life following the extinction event.

"We knew that lack of oxygen in the oceans played a key role in the extinction and recovery processes, but we are still discovering how exactly it was involved. Our findings about the chemistry of the ocean at the time provide us with a clearer picture of how this complex process delayed the recovery of life for so long," said Dr Matthew Clarkson, of the University of Edinburgh's School of GeoSciences and lead author of the study, in a statement.

For the study, the researchers analyzed rocks unearthed from six sampling sites in Oman, which was formed in an ancient ocean around the time of extinction, using precise chemical techniques.

The researchers discovered that water during the recovery period is indeed lacking oxygen. However, the researchers were not able to detect the toxic sulphide in their samples. Instead, they found out that the water is rich in iron during that time.

Furthermore, their analysis showed that oxygen levels varied at different depths of the ocean. Shallower waters contained oxygen for a short period of time, allowing the support of diverse marine life for a brief period of time. However, low oxygen levels were present at some depths, restricting the recovery of marine life.

Researchers are still unable to pinpoint the exact cause of the delayed recovery period, but they believe that the increased run-off from erosion of rocks on land due to high global temperatures likely triggered anoxic conditions in the ocean.