Neanderthal and modern human cranial differences. On the left is a Neanderthal from France (cast of La Ferrassie 1) and on the right is a recent modern human from Polynesia.
A cave in the northern Caucasus Mountains may hold a key to the long-standing mystery of why the Neandertals, our closest relatives, went extinct. For nearly 300,000 years the heavy-browed, barrel-chested Neandertals presided over Eurasia, weathering glacial conditions more severe than any our own kind has ever faced. Then, starting around 40,000 years ago, their numbers began to decline. Shortly after 28,000 years ago, they were gone. Paleoanthropologists have been debating whether competition with incoming modern humans or the onset of rapidly oscillating climate was to blame for their demise. But new findings suggest that catastrophic volcanic eruptions may have doomed the Neandertals—and paved the way for modern humans to take their place.
Researchers led by Liubov Vitaliena Golovanova of the ANO Laboratory of Prehistory in Saint Petersburg studied the deposits in Mezmaiskaya cave, located in southwestern Russia. First discovered by archaeologists in 1987, the cave once sheltered Neandertals and, later, modern humans. Analyzing the various stratigraphic layers, the scientists found layers of volcanic ash that, based on the geochemical composition of the ashes, they attribute to eruptions that occurred in the Caucasus region around 40,000 years ago. Because the cave preserves a long record of Neandertal occupation preceding the ash layers but no traces of them afterward, the team surmises that the eruptions devastated the locals.
Read more here Scientific American