The most famous mass extinction is the one that ended the dinosaurs and some 50 percent of life on Earth about 65 million years ago. The culprit was mostly the impact with a large asteroid, about seven miles across, that hit the Yucatán Peninsula in Mexico. I wrote about some of the scary details a couple of months ago.
But the Yucatán event pales in comparison with the mass extinction that happened 252 million years ago, at the end of the Permian period. Scientists estimate that about 95 percent of all marine species, and an unknown "but probably comparable percentage of land species, went extinct in a geological heartbeat," as Alanna Mitchell reported recently in The New York Times.
Although an impact has been proposed as a possible culprit, recent work suggests that the vast die off was related to a lack of oxygen in the water, coupled to an excess of carbon dioxide, which implied in an increase in ocean acidity and water temperatures. A nonlinear feedback from these effects amplified the damage. Corals and sea sponges were devastated, and trilobites were gone.
In a paper for Annual Reviews of Earth and Planetary Sciences, Jonathan Payne, from Stanford University, and Matthew Clapham, from the University of California at Santa Cruz, suggest that the catastrophe coincided with one of Earth's largest continental flood basalt provinces, the Siberian Traps. In other words, a gigantic volcanic eruption launched enormous amounts of gases into the atmosphere, compromising global ocean chemistry, causing climate change and, possibly, the destruction of the ozone layer, which would explain the land extinction. In studying the climate change in the past or present, the coupling of the oceans with the atmosphere is crucial.
The extinction serves as a laboratory to what is going on now, as even larger amounts of CO2 are being launched into the atmosphere, causing the rapid acidification and warming of the oceans. In 1996, Andrew Knoll, a Harvard geologist, and collaborators suggested that increases in atmospheric CO2 had severe consequences for marine life in the late Permian Earth. "Today, humans turn out to be every bit as good as volcanoes at putting carbon dioxide into the atmosphere," he said to the NYT's Mitchell.
Of course, we are not at the late Permian, a time when all continents were united as one, Pangea, and the ocean's chemistry was different. But the lesson is loud and clear for those who choose to hear it: increased concentrations of atmospheric CO2 acidify the oceans and kill marine life. The key difference is that now we are the main culprits and can take measures to attenuate the ensuing changes.