At the time of the third of the Big Five extinctions, the Permian-Triassic, there was only one massive continent and one massive ocean, conditions that disrupted ocean circulation and inhibited oxygen circulation in an already warm world, according to Lee Kump, a geoscientist at Pennsylvania State University. That set the stage for the ultimate trigger, a series of massive volcanic eruptions in Siberia.
The eruptions pumped massive amounts of carbon dioxide into the atmosphere. This warmed the ocean further, exacerbating its oxygen problem. Meanwhile, more storms on land washed more oxygen-eating nutrients into the ocean. Bacteria began producing hydrogen sulfide, which was ultimately expelled into an atmosphere already toxic with carbon dioxide, according to Kump.
A comparison of carbon dioxide release then versus now is telling, Kump said. Siberian volcanoes emitted tens of thousands of gigatons of carbon dioxide into the air over what was probably thousands of years. Humans currently are producing 9 gigatons per year from fossil fuel reservoirs that contain up to 4,000 gigatons.
The rate of carbon dioxide release matters, Kump said, because life has to have time to adapt.
"It's: Would you rather be squeezed or punched?" Kump said. "The Permian extinction was a squeeze that gradually got tighter and tighter … It may ultimately have been more fatal than the punch we are going to get, but the punch is going to hurt more."
Crumbling at the base
The parallel in ocean chemistry between the past and present isn't limited to oxygen depletion. The Permian ocean became more acidic as the climate changed, just as the modern ocean is doing.