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Analytical Chemistry

Neanderthals May Have Been Cave Artists

Uranium-to-thorium decay method identifies age of calcite deposits on top of Paleolithic cave art in Spain

by Sarah Everts
June 18, 2012 | A version of this story appeared in Volume 90, Issue 25

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Credit: Pedro Saura
This cave art was made around 37,300 years ago, when both Neanderthals and humans inhabited Europe.
Ancient cave art possibly made by Neanderthals, or the earliest humans
Credit: Pedro Saura
This cave art was made around 37,300 years ago, when both Neanderthals and humans inhabited Europe.

Scientists spelunking in 11 Spanish caves have used an uncommon radioactive-decay method to date Paleolithic wall art, showing that some of the paintings may have been made by either Neanderthals or the earliest humans in Europe (Science, DOI: 10.1126/science.1219957). The dating method uses mass spectrometry to measure trace levels of uranium and thorium found in thin crusts of calcite that build up on the cave art, explains Alistair W. G. Pike, a radioisotope specialist at the University of Bristol, in England, who led the study. The water that deposited this calcite contained trace amounts of dissolved uranium but no thorium. Thus, any thorium present in the calcite is the result of uranium’s radioactive decay into thorium. By comparing ratios of thorium and uranium in calcite crusts on the art, the team was able to establish minimum ages for some 50 Spanish cave paintings. In three cases, the art was dated to between 35,600 and 40,800 years ago. Neanderthals were present in Europe during this era, and modern humans likely appeared there around 41,000 to 42,000 years ago, says João Zilhão, a Neanderthal expert at the University of Barcelona who was involved in the study.

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