Today's selection — from The Horse by Wendy Williams. Climate change has varied widely through time. The temperature increase during the Paleocene-Eocene Thermal Maximum (PETM) of 56 million years ago, in which global temperatures rose at least 5°C for 200,000 years, may have helped lead to the rise of mammals: “[During the PETM] it was hot. … In fact, it was as though there was a sudden explosion of heat, as remarkable in its own way as the fall of the asteroid had been 10 million years earlier. Curiously, this explosion of heat also marks the appearance of Polecat Bench, [Wyoming's] horses and primates. This was a time when temperatures in some places shot up by 6 or 8 degrees Celsius in a very short time period, lingered at those heights, then, almost as suddenly, dropped back down. The cause of this heat spike remains elusive, but it may have been due to large bursts of methane that bubbled up from the deep ocean.
…”It's hard for us to imagine in our twenty-first-century world, where we accept the cruel reality of sweltering summers and freezing winters, but for a good deal of Earth's history, including most of the Eocene, the planet enjoyed fairly uniform temperatures. For example, during the Eocene, the world north of the Arctic Circle was so warm that crocodiles flourished there. There were no ice caps, of course, and so much freshwater flowed into the Arctic Ocean that a layer of freshwater sat like a lens over the salt water. The freshwater Azolla fern was plentiful. Forests of redwoods and walnut trees grew there. Paleontologists have found the remains of giant ants usually associated with the tropics.”