What do 20,000-year-old footprints in Tibet mean?

Scientists have discovered footprints and handprints made 20,000 years ago, high on the Tibetan Plateau, during the Ice Age. Previous researchers believed that this area was covered with a thick glacier at that time and that humans only settled there about 4,000 years ago. In fact, a very hot spring situated 85km from Lhasa, the capital of Tibet, would have made it habitable – as the footprints prove.

The spring water is rich in minerals and gases which precipitate out to form a soft mud. This then solidifies, forming a hard limestone called travertine. Nineteen hand and footprints have been found in the resulting marble-like rocks.

Quartz gives off light in proportion to the time that has passed since it was last exposed to sunlight – this is called thermoluminescence. In this case, grains of quartz trapped in the travertine containing the footprints indicated that the area was inhabited some 16,000 years earlier than previously thought.

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