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A couple of groups dug pits, filling them with coals and then lining them with either wet clay or a deer hide. Others poured water into birch bark or pig stomachs (procured from a Chinese supermarket). One group hung a deer hide from a tree and started heating small rocks in a fire—a technique inspired by the discovery of fire-cracked rocks in Paleolithic sites. These rocks had split and changed in distinct ways that suggested repeated heating and cooling. Archaeologists think that these stones were heated in fires and then dropped into water for cooking.

But you can’t use just any old rocks for boiling. “The stones are the most tricky part,” Langley says. Wet stones, such as those that have been sitting in a river bed, will explode when the water inside turns into steam. So will stones with air trapped inside them. “Things like granite and basalt are very good,” he says. For safety reasons, Langley provided the students with massage stones that he knew would not explode. Still, the students had to heat the stones gradually to make sure that they did not crack at all. They ended up slowly nudging the stones into the fire over the course of 10 to 15 minutes. Using multiple stones, they were able to get the water inside the deer hide to boil.

Another group was also attempting to boil water inside a deer hide hung directly over a fire—a technique admittedly less grounded in physical evidence from archaeological sites. In 2015, John Speth, a retired anthropologist at the University of Michigan, wrote a paper pointing out that you can actually boil water in a plastic water bottle. The paper, he was happy to explain to me, was inspired by watching the reality show Survivorman, in which the outdoor expert Les Stroud boils water in a plastic bottle, with his son. Speth quickly found YouTube videos and other evidence of people heating water in paper cups, coconut shells, bamboo tubes, wooden bowls, and even leaves. It turns out that as long as the cooking container is filled with water, it does not get hot enough to ignite.

But when Speth began talking with other archaeologists about this, he found that they had rarely thought about Paleolithic humans boiling water this way, using seemingly flimsy and flammable containers long before the introduction of pottery. However, ethnographers in the 19th and 20 centuries documented the Celts, Assiniboin, Cree, Ojibwa, and Blackfeet cooking without stones in birch bark, hides, and animal stomachs. These organic materials would have rotted, of course, leaving no artifacts for archaeologists to study. Speth wondered if humans could have boiled liquids this way long before the evidence showed up in the archaeological record.

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