And that’s because the uranium and thorium have different solubilities.
So uranium is very soluble, which means it gets dissolved up by these waters. The 238-uranium, which is the isotope at the beginning of decay chain we are interested in, has a half-life of about 4 and 1/2 billion years.
You were looking at crusts that had formed on top of them. So these crusts are made from calcium carbonate and they’re essentially tiny speleothem. And when it percolates through the limestone below, it dissolves up small amounts of calcium.
So secondary carbonate formations along the lines of stalagmites and stalactites. Rain water passes through the soil profile above a cave. When this water enters the cave below, the carbon dioxide is released.
CHRISTOPHER STANDISH: Well this is for a different motif to the ones that we have the minimum ages of 64,000 years.
Hands stencils and general patches of pigment on stalagmitic formations.
IRA FLATOW: Give us an idea of how you dated the paintings.
Researchers could only speculate: Were the symbolic masterpieces created by early modern humans or were they done by the hands of Neanderthals? That’s changing now because new research makes exactly that claim for Neanderthals.
Could these stencils be evidence of Neanderthals’ cognitive abilities? A research team from University of Southampton and the Max Planck Institute for Evolutionary Anthropology studied red and black pigmented cave art—from animals, geometric patterns, and hand stencils—in three of the caves in a grotto in Southern Spain. A team of scientists are using uranium dating of tiny calcite crusts over cave paintings in Spain to say that these paintings had to be older than 60,000 years. Christopher Standish, a co-author on that paper and an archaeologist at the University of Southampton in the UK. IRA FLATOW: So how sophisticated is the art in these caves?