The early age of mammals came at a chaotic time in the development of the Earth: The planet was still struggling with the disappearance of the dinosaurs and the newest crater was a smoldering system of hydrothermal vents at the time, writes The Atlantic.
Eventually, life settled into a rhythm, and mildly modern mammals started to appear. Within a few million years, mammals began to evolve, like when the first lemur-like primates leapt from the treetops or when early whales walked on all fours.
But The Atlantic writes that the most astonishing thing about this early age of mammals is that it was unbelievably hot, so hot that around 50 million years ago there were crocodiles, palm trees and tiger sharks in the Arctic Circle. There were potentially even dead zones spanning the tropics, where it was too hot for animal or plant life of any sort. The ancient atmosphere was around 1,000 parts per million (ppm) of carbon dioxide.
And there are disturbing parallels to the climate trends today.
Last week, David Naafs, an organic geochemist at the University of Bristol, and his colleagues released a study that reconstructs temperatures on land during this time of ancient high-CO2. According to The Atlantic, Naafs and his team The team found that in the ancient U.K., Germany, and New Zealand, life endured mean annual temperatures of 23–29 degrees Celsius (73–84 degrees Fahrenheit) or 10–15 degrees Celsius (18–27 degrees Fahrenheit) warmer than modern times.
“These wetlands looked exactly how only tropical wetlands look at present, like the Everglades or the Amazon,” Naafs said to The Atlantic. “So Europe would look like the Everglades and a heat wave like we’re currently experiencing in Europe would be completely normal. That is, it would be the everyday climate.”
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