But are those human hands?
The crusts incorporate small amounts of uranium, which decays into thorium over time.
Modern humans arrived in Europe from Africa some 41,500 years ago.
Another possibility is that the paintings werent made by humans at all, but by Neanderthals.
Many scientists had long doubted whether Neanderthals were capable of producing symbolic art.
It does however surprise archaeologists like Pat Shipman, who has spent a lifetime studying symbolic behavior.
She wonders why Neanderthals waited until about the time humans arrived to get the itch to paint.
Entrance to the cave of El Castillo.
Source:Scientific American/National Geographic/NPR/University of Bristol
