The site is too far inside a cave for the ash to be caused by a lightning strike and the spontaneous combustion of bat guano was ruled out.
Evidence is quite thin on the ground, but for example, researchers found evidence of ash as well as burnt bone fragments in a one-million-year-old sediment layer in the Wonderwerk Cave in South Africa. The site is too far inside a cave for the ash to be caused by a lightning strike and the spontaneous combustion of bat guano was ruled out.