The Permian period was hot, hot, hot: Around 270 million years ago, air temperatures near the equator may have soared to almost 74º Celsius or 165º Fahrenheit, scientists report March 18 in Geology. That’s far hotter than anywhere on Earth today.
“I can’t even imagine what it would have been like,” says Neil Tabor, a sedimentary geochemist at Southern Methodist University in Dallas, who wasn’t involved in the research. The intense heat may explain why plants and animals vanished from parts of the tropics at this time, he says, a disappearance that preceded the mass extinction that ended the Permian period 252 million years ago. Only microbes that thrive under extreme conditions could have survived such temperatures.
Evidence for the sweltering heat comes from Kansas, which was near the equator during the Permian, when the continents fused to form Pangaea. Previous work showed that, in the middle Permian, western Kansas was a desert where lakes of brine repeatedly formed, evaporated and left behind salt deposits. Geologist Kathleen Benison of West Virginia University in Morgantown and a colleague had determined that air temperatures there reached 50º C, no hotter than California’s Death Valley today.
Benison and Jay Zambito, also of West Virginia, were surprised to find the even hotter temperatures while investigating another site in western Kansas. They looked at crystals of halite, or rock salt, which act as natural thermometers. As the crystals grow in evaporating lakes of brine, they trap microscopic bubbles of saltwater. In the lab, scientists can estimate the temperature at which the bubbles formed, thereby taking the temperature of the ancient brine itself. Each bubble, Benison says, “is a very specific snapshot for a single time and place.” Since the brine pools were only tens of centimeters deep, the bubbles are good proxies for air temperature, she adds.
The team collected almost 400 temperature readings across 15 layers in sediments buried roughly 600 to 800 meters deep. The whole record corresponds to about 270 million years ago, but how much time elapsed across the layers is unknown.
Near the beginning and end of the record, average air temperatures were in the 20s and 30s Celsius.Temperatures spiked in the middle layers to an average of almost 45º C, with daytime temperatures ranging from about 25º C to almost 74º C. Benison and Zambito plan to investigate temperatures over a larger geographic area to see whether the sizzling heat was a regional phenomenon.
But some researchers are not convinced that the team actually found such extreme temperatures. “It’s a question of whether or not they’ve measured the air temperature,” says geochemist Ron Spencer of the University of Calgary in Canada. In some modern salt pans, even shallow brine can be much hotter than the air because it retains heat better.
If the air temperatures are valid, they create a mystery. “It’s unclear at the moment how we could get such extreme conditions at this place,” Tabor says. Climate simulations can’t yet reconcile how the area could be that hot and still have liquid water at the surface.