Two fascinating pieces of information come from a Nature article about the discovery of million year-old ash in a cave far beneath the ground.
1. Lightning could not have reached this part of the cave to start a fire of organic materials there, so the researchers surmise that ancestors of modern humans must have either created fire in the cave or transported fire to the cave. The implication of their discovery is that ancestors of modern humans already had some control over the use of fire one million years ago. Homo erectus, and perhaps other species of humans, were living at that time, but remains of Homo sapiens of anything close to that age have not been found.
2. One of the alternative explanations that researchers eliminated was that the fire could have started in a pile of bat guano. Apparently, piles of decomposing bat guano can become so hot that they light on fire all by themselves. No traces of bat guano were found on the site, however.