…How do historians date these works?
There are two main methods to determining the age of the cave art. The first is to use the surrounding earth layer to arrive at a date (chemically test how old the dirt is). The second is to use a process called radiocarbon dating, and it examines organic (once-living) objects found near the artifact. In principle, I'm told it works this way: basically all living organisms contain a certain amount of Carbon 14. After an organism dies, the Carbon 14 loses its radioactivity at a known rate. By finding how much radioactivity is left in the charcoal, or carbonized bones, etc., one can arrive at an estimate of how old it might be. As I mentioned earlier, these paintings survived throughout history because of their safe, protected location in the backs of caves, away from the harmful effects of wind and rain.