Figuring out when humans first arrived in a location is surprisingly tricky. Sometimes, you find a nice chunk of pottery or something, but oftentimes artifacts aren't as easy to find. Predators can leave bones that look a lot like ones that a human might butcher, and a natural fire leaves coal much the same as a human one does. So what do humans leave behind everywhere that's unique to them? Poop. Well, human poop, anyway.
A new piece of research in PNAS reveals a biomarker unique to human feces — which in turn offers evidence for when people arrived at Lake Liland in the Lofoten Islands in northern Norway. Using sediment cores from the bottom of the lake, the researchers were able to create a continuous record of 7,000 years thanks to radiocarbon dating and known volcanic events.
However, a bit more than 2,000 years ago, coprostanol first turns up in the core. That's a molecular marker formed by the digestion of cholesterol in the human stomach, and it showed up alongside similar markers that come from sheep and cattle. Since fecal matter tends to make its way into local bodies of water, it settled at the bottom, and became part of the sediment. Combine that with signs of large scale fires, and you have early evidence of humans.