The torch marks on the walls of Hourglass Cave are not simply interesting as human artifacts.

They are potentially datable evidence — and understanding how researchers use them as evidence requires understanding what they are and how they form.

When an ancient torch — made from organic material that burns with a sooty flame — passes close to a cave wall, carbon particles from the combustion deposit on the wall surface.

These deposits are usually black or dark brown, and under the right conditions they can adhere to cave surfaces for very long periods.

The same basic principle accounts for the survival of lamp soot in the painted caves of Europe, where charcoal and grease lamp marks have persisted for tens of thousands of years on cave walls that were otherwise undisturbed.