Scientists have discovered that prehistoric cave paintings took up to 20,000 years to complete. Rather than being created in one session, as archaeologists previously thought, many of the works discovered across Europe were produced over hundreds of generations who added to, refreshed and painted over the original pieces of art.
     Until now it has been extremely difficult to pinpoint when prehistoric cave paintings and carvings were created, but a pioneering technique is allowing researchers to date cave art accurately. Dr Alistair Pike, an archaeologist at Bristol University who is leading the research, said: "The art gives us a really intimate window into the minds of the individuals who produced them, but what we don't know is exactly which individuals they were as we don't know exactly when the art was created. If we can date the art then we can relate that to the artefacts we find in the ground and start to link the symbolic thoughts of these individuals to where, when and how they were living."
     Hundreds of caves have been discovered across Europe with elaborate prehistoric paintings and carvings on their walls. It is thought the designs were created up to 40,000 years ago. Traditional dating techniques have relied on carbon dating the charcoal and other pigment used in the paintings, but this can be inaccurate as it only gives the date the charcoal was created not when the work was crafted. "When you go into these caves today there is still charcoal lying on the ground, so the artists at the time could have been using old charcoal rather than making it fresh themselves," explained Dr Pike. "If this was the case, then the date for the painting would be very wrong. For carvings, it is virtually impossible to date as there is no organic pigment containing carbon at all."
     The scientists have used their technique to date a series of famous Palaeolithic paintings in Altamira cave near Santillana del Mar, northern Spain. The elaborate works there were thought to date from around 14,000 years ago, but Dr Pike discovered some of the paintings were between 25,000 and 35,000 years old. The youngest paintings in the cave were 11,000 years old. Dr Pike said: "We have found that most of these caves were not painting in one go, but the painting spanned up to 20,000 years. This goes against what the archaeologists who excavated in the caves and found archaeology for just one period.
     Dr Pike and his team were able to date the paintings using a technique known as uranium series dating, which was originally developed by geologists to date rock formations such as stalactites and stalagmites in caves. By comparing the ratio of uranium to thorium in the thin layers on top of the cave art, the researchers were able to calculate the age of the paintings. The researchers have also applied their technique to engravings found in rocks around Cresswell Crags in Derbyshire, which are Britain's only examples of ice age cave art. They proved the engravings were made at least 12,000 years ago.
     When combined with evidence from archaeology and other disciplines, the new dating technique promises to let researchers create a more robust and detailed chronology of how humans spread across Europe at the end of the last ice age. "It's a big step in understanding the timing of how cave art was produced," adds Pike. "It is also shedding light on the reasons for its production - why do you get a sudden flourishing of cave art at certain periods?" Last year the team visited around ten Spanish caves and took samples from four, ending up with 20 usable dates; a three-year research grant from NERC has now provided enough funding to get around 130 more dates. This would more than double the number of dates for cave art of this period for the whole of Europe.

Sources: Planet Earth Online, Telegraph.co.uk (5 October 2008), BBC News (7 October 2008)