Dr. Dirk Hoffmann, researcher at the Centro Nacional de Investigación sobre la Evolución Humana (CENIEH), is a member of the team of scientists led by Dr Alistair Pike, from the University of Bristol, UK, who is this week Science`s front cover with a paper entitled "U-Series Dating of Paleolithic Art in 11 Caves in Spain", which places Europe's oldest rock art in El Castillo (Cantabria, Spain) with over forty thousand years of age, using the uranium-series dating method.
 
This method has succeeded in dating the rock art in Europe, and as Dr. Hoffmann explains, despite the great advances in dating techniques,” it is extremely difficult to determine the age of thin layers of pigment found in the caves”.
 
On the one hand, traditional methods, such as radiocarbon dating, do not work where there is no organic pigment, and on the other hand,  researchers are often limited to reconstruct the chronology by comparing the styles of the paintings and, when possible, relating them to human remains or artifacts found in the immediate environment.
 
 Rock art is usually found in carbonate terrains, which most of the caves around the world have developped. Stalagmites, stalactites and similar calcite formations, collectively known as speleothems, contain small amounts of uranium and are therefore susceptible to undergo this method of dating, "the most effective we have for this type of materials, "says Dr. Hoffmann.
 
Another advantage of this technique s is that it causes no damage to the paintings, "even though, removing these materials led to ha better view of the pigments. We could say that we clean them , "says this expert in the dating of speleothems.
 
"50 grains of rice"
Another key to the reliability of the results published in this work, which now appears on the cover of Science, is that it has improved the procedure used in both a qualitative and quantitative way. "The key development was our method to date tiny tiny calcium carbonate deposits similar to stalactites. We can now date samples of just 10 milligrams – about as small as a grain of rice.  This has allowed us to find samples that had formed directly on top of hundreds of paintings, whereas the larger stalactites were much less frequent”, explains Dr. Hoffmann
 
Finally, the large amount of material analyzed from different environments was essential: 50 samples from 11 caves in northern Spain, such as Cantabrian caves of Altamira and El Castillo and the cave of Tito Bustillo in Asturias. The quantity and variety of the samples ensure that the dating is significant.
 
Sapiens versus Neanderthals
According to the results of this project funded by the UK’s Natural Environment Research Council (NERC), the Paleolithic cave art in Europe began 10,000 years earlier, implying that the paintings of the three caves above mentioned  could have been made by early modern humans or even by the Neanderthals. 


This new date, which opens the way to speculation about the authorship of the first cave paintings, since the two species coexisted in Europe, “has encouraged us to prepare a new project involving Spanish caves and other ones in France, Italy and Portugal, although it will only be feasible if we get the necessary funding," concludes this German researcher who has worked in the CENIEH since 2009.