A study conducted at Stanford University in the United States concluded that the first mass extinction on Earth decreased the oxygenation of the oceans for more than 3 million years.
This extinction occurred at the end of the Ordovician period, 444 million years ago. At that time, the continents had not yet separated and formed Pangea, and life was mostly marine. It is estimated that 85% of the species did not survive the event.
At that time, the world temperature dropped and an ice age began. When temperatures rose again, sea levels increased and water oxygenation decreased, causing what scientists call "anoxia".
Other mass extinctions have had similar effects, but not for so long. "For marine life, it was really a very bad time to be alive," says Erik Sperling, assistant professor of geological sciences at Stanford and one of the study's authors.
The research also states that anoxia contributed to a second mass extinction.
The study of ocean conditions in the past can help scientists understand the climate change we are experiencing – studies show that the level of oxygen in the oceans has already decreased by about 2%.
"There is no possibility that this low oxygen level will not have a severe effect on diversity," says Richard George Stockey, who also participated in the study.