Invisible to the human eye, cryptotephra is a fine volcanic glass that is blasted out of erupting volcanoes along with ash. It leaves behind a hidden layer, in the earth, which has now been detected, giving clues about why the Neanderthals died out.
About 40,000 years ago, a layer of cryptotephra particles carpeted a huge area of Central and Eastern Europe after a massive volcanic eruption in Italy called the Campanian Ignimbrite (CI). This eruption, and the resulting environmental and climatic disruption, has been suggested as a factor in the extinction of the Neanderthals.
Interaction with us, modern humans, is one of the other possibilities. Neanderthals, who were our closest relatives, had been living in Europe for hundreds of thousands of years. But all physical evidence of them disappears after about 30,000 years ago. Early modern humans were known to have arrived in Europe at least 35,000 years ago, having originated in Africa, but precise dates, and the length of time they overlapped with the last Neanderthals, are unclear.