Remembering The Paleocene-Eocene Thermal Maximum For When It Comes Around Again
There was a time when alligators slid through weed-choked swamps near the North Pole. Some 55 million years ago—just around 10 million years after the mass extinction that killed T. rex and most of its kin—the average global temperature sat more than 20°F higher than it does today. Subtropical forests spread to northern latitudes, and mammals thrived in lush new habitats.
The toasty weather had nothing to do with the event that killed the dinos. The driver for the climatic shift came not from above, but from below—in Earth’s oceans. Paleontologists and geologists suspect that some amount of natural warming that took place during the Paleocene, or the period following the die-off, caused great deposits of crystallized methane to transform into gas. Seabeds belched the excess out into the water and the air, which was bad news for the planet: Methane is a greenhouse gas far more potent than carbon dioxide. The globe rapidly warmed in response—jumping about 10°F in less than 20,000 years—and held steady for some 70,000 more before starting a long and slow recovery. Paleontologists call this hot spot the Paleocene-Eocene Thermal Maximum (PETM). It’s a time when subtropical forests spread over the continents and new animals got to stake their claims on the planet, all thanks to an atmosphere and oceans in turmoil. This part of the fossil record is a remnant of the past, but it may also be a preview of our future.
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In a sense, the ocean is like a big conveyor belt. Typically, cold air and salty water mix in the Southern Hemisphere to create dense, cool “deep water,” which keeps things moving. The toastier PETM climate, though, caused more rain to fall at the North Pole, which weakened currents and shifted things around. In less than 5,000 years, cold air and salty oceans were instead mixing in the North Atlantic. The change in flow warmed the ocean even more. Higher temperatures increased the metabolisms of local critters and, as a result, their demand for food. But hotter water also holds less oxygen, so it’s not hard to see how the conditions of the PETM put marine life in an impossible situation: Animals needed more food to get by, while the lack of oxygen made the environment harsher and kept nutrients scarce.
The climate effects lasted 100,000 years, and some organisms couldn’t keep up with the change. Deep-sea varieties of so-called “armored amoebas” (aka benthic foraminifera or forams), a favorite of paleontologists studying evolution and extinction because of their abundance in the fossil record, suffered a major die-off. More than 35 percent of their species went extinct, marking their only significant crisis in the last 90 million years. Forams have long been a staple food of many small ocean creatures, so paleontologists suspect their absence made a big difference.
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https://www.popsci.com/environment/petm-climate-change/