A revolutionary dating technique developed at the University of Wales, Aberystwyth has revealed that two pieces of ochre discovered by archaeologists working in South Africa are probably the earliest known works of art.

The two abstract representations engraved on pieces of red ochre were recovered from the Middle Stone Age layers at Blombos Cave on the southern Cape coast of the Indian Ocean in South Africa, 200 kms east of Cape Town by Prof Chris Henshilwood. Luminescence dating has shown that they are approximately 77,000 years old.

The findings are published in this weeks (Jan 10) on-line edition of Science - the journal of the American Association for the Advancement of Science.

Prior to this discovery by Prof. Chris Henshilwood and his team the earliest forms of art were thought to be cave paintings in southern France and northern Spain which are dated to 35,000 years ago. The engravings discovered in South Africa support the idea of the emergence of modern human behavior in the region at least 35,000 years earlier than in Europe.

The team from the Aberystwyth Luminescence Laboratory led by Dr Geoff Duller visited Blombos Cave in February 2001 and collected samples of sand from a dune which had formed over the layers containing the ochre.

Working in the laboratories at Aberystwyth under dark room conditions (usually associated with the development of photographic films), the team used optically stimulated luminescence which enabled them to calculate when a particular grain of sand was last exposed to light. Zenobia Jacobs, a doctoral student on the project, measured over 1800 individual grains of sand.

Once buried, grains of sand are exposed to natural radiation and part of the energy of this radiation is stored in the grains. The amount of energy absorbed is calculated by stimulating the grain of sand with a green laser, which in turn releases the energy in the grain as ultraviolet light. By measuring the intensity of this light the team are able to date the time at which each grain of sand was buried.

According to Dr Duller, the layer of sand in the cave where the ochres were discovered was probably due to the sand being blown in from the nearby beach.

“By dating the sand in the dune overlying the layers where the artefacts were discovered we have been able to give a minimum age for the time when they became buried. It follows therefore that any artefacts below this level are probably older.

“Thermoluminescence dating of burnt rock fragments from within these lower levels by a French group have confirmed this,” he said.

“The project presented a number of challenges as we needed to ensure that the sand grains being dated were all of the same age. The cave itself is developed in aeolianite (a type of sandstone) and, over a period of time, grains of sand from the caves roof might have become mixed up with the sand which was blown in. Grains from the roof would have given misleading dates, so the team has worked painstakingly to ensure that no such grains were used in the age analysis,” he added.

Such detailed studies were made possible by cutting-edge equipment that Dr Duller and his team at Aberystwyth have pioneered in collaboration with a Danish group. This equipment, funded by NERC, enables the luminescence signal from each grain of sand to be measured in rapid succession. Prior to this development, the process was very time consuming.

“The next phase of the work is to analyse samples taken from the layers where the ochres were discovered. Analysing the first set of data has taken a full year, and we estimate that it will take possibly a year and half to sample, test and analyse the 1m deep occupation layers in the cave,” said Dr Duller.

• Story originally published by:
NewsWales / Wales - Jan 11.02

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