Cave paintings (also known in archaeology as "parietal art") are paintings found on cave walls and ceilings, and especially those of prehistoric origin, which date back to some 40,000 years ago (around 38,000 BCE) in both Asia and Europe. The exact purpose of the Paleolithic cave paintings is not known. Evidence suggests that they were not merely decorations of living areas since the caves in which they have been found do not have signs of ongoing habitation. They are also often located in areas of caves that are not easily accessible. Some theories hold that cave paintings may have been a way of communicating with others, while other theories ascribe a religious or ceremonial purpose to them. The paintings are remarkably similar around the world, with animals being common subjects that give the most impressive images. Humans mainly appear as images of hands, mostly hand stencils made by blowing pigment on a hand held to the wall.