The Great Dying

At the end of the Permian Period, which also is the end of the Paleozoic Era about 252 million years ago, approximately 95% of the species known from fossils went extinct. This is the same time, with very little uncertainty, as the greatest volcanic outpouring on Earth in the last 500 million years.

The rise in CO₂ from the volcanic eruptions caused warming. (Volcanoes generally cause cooling over short times, such as their role in causing the Little Ice Age of a couple centuries ago, but volcanoes raise temperatures over longer times, such as their role in warming the end of the Permian.

Do you want to learn more?
Read the Enrichment titled Volcanoes Cool and Warm, without Doubletalk.

The volcanic eruptions are estimated to have raised CO₂ much more slowly than humans are doing, but the volcanoes didn't run out of CO₂ as rapidly as we will run out of fossil fuels, so the event back then lasted longer. Our understanding indicates that the extra warmth from the CO₂ accelerated rock weathering, providing extra fertilizer reaching the ocean. This would have helped make extensive “dead zones” as parts of the ocean ran out of oxygen, aided by the lower oxygen level in the water caused by the higher temperature. Sediments from that time contain special “biomarker” molecules made by green sulfur bacteria that photosynthesize with the poisonous-to-us gas hydrogen sulfide, indicating loss of oxygen and rise of hydrogen sulfide in the ocean. New data also suggest the Earth became so hot that the few remaining large creatures could not live in the tropics immediately after the extinction, but only closer to the poles.

Trilobites (specimen from the Grand Canyon) and eurypterids (the State Fossil of New York) lived for well over 100 million years, but did not survive the great dying at the end of the Permian.

Source: Pictures from the US National Park Service, trilobite and eurypterid.

We do not expect the warming in our near future to produce anything nearly so bad, but fertilizer runoff from our fields and warming from our CO₂ can contribute to oceanic “dead zones”. And, we cannot rule out the possibility that beginning or near the end of this century, we could make the Earth so hot that living unprotected in the tropics becomes difficult or even impossible for us and some other large creatures.