...First, the human fossils cannot be directly dated, since the site is a world heritage area and the fossils are protected by Laotian laws.Second, there are very few animal bones and no suitable cave decorations, either of which might be used for dating.And third, the entrance of the site is wide and steep. This means any charcoal found in the cave, which is useful for dating, may well have come from outside—so it has little relation to the age of the sediment inside.This means the backbone of the timeline must be established by the dating of the sediment itself using...