18 October 2011

Ochre find reveals ancient knowledge of chemistry

The oldest ochre-processing toolkits and workshop ever found have been unearthed in South Africa, indicating that as far back as 100,000 years ago, humans had an elementary understanding of chemistry.
Ancient ochre processing tools

Abalone shell, Tk1-S1, in laboratory after removal of the quartzite grinder cobble and some of the ochre rich deposit. The cut sand area is where a sample was removed for analysis.
Credit: Science/AAAS

Ancient ochre processing tools

The Tk1 toolkit with abalone shell, Tk1-S1 in situ and before excavation from the 100,000 year old Middle Stone Age levels at Blombos Cave, South Africa.
Credit: Science/AAAS

SYDNEY: The oldest ochre-processing toolkits and workshop ever found have been unearthed in South Africa, indicating that as far back as 100,000 years ago, humans had an elementary understanding of chemistry.

South Africa’s Blombos Cave lies within a limestone cliff on the southern Cape coast, 300 km east of Cape Town. It’s known for its 75,000-year-old rich deposits of beads, bone tools and ochre engravings. Some engravings date to 100,000 years ago.

Archaeologist Christopher S. Henshilwood from the University of Witwatersrand in Johannesburg and University of Bergen, Norway has been excavating at the site since 1992, and has reported the discovery of a mixture, rich in ochre, stored in two abalone shells, dating to the Middle Stone Age 100,000 years ago, in the current issue of Science.

Made from an array of materials, this mixture, which could have been used for wall, object and skin decoration or skin protection, indicates the early technological and behavioural developments that occurred in the people that originally used the site.

“[Judging from] the complexity of the material that has been collected from different parts of the landscape and brought to the site, they [the people] must have had an elementary knowledge of chemistry to be able to combine these materials to produce this form. It’s not a straightforward process,” said Henshilwood.

An ancient pigment

Ochre is a term used to describe an earth or rock containing red or yellow oxides or hydroxides of iron. It can be used to make pigments ranging from golden-yellow and light yellow-brown to a rich red. Its use spans the history of humans from those living more than 200,000 years ago to modern indigenous communities.

The Blombos Cave discovery is the earliest known example of a pigment-producing workshop. The two toolkits were discovered in situ, and they included an array of objects including samples of ochre, bone and charcoal, as well as grindstones and hammerstones.

They were buried within quartz sediments, which researchers at Wollongong University dated to 100,000 years ago using a technique known as Optically Stimulated Luminescence dating.

Complicated process

Judging by the toolkits, which show signs of wear, Henshilwood and his team were able to extrapolate the process used to produce the ochre mixture.

First pieces of ochre were rubbed on quartzite slabs and crushed to produce a fine, red powder. This was combined with fatty, crushed-up mammal bone, the traces of which show signs that it was heated before being crushed.

The ochre powder and the bone pieces were mixed with charcoal, stone chips, quartz grains and a liquid, perhaps water, which was poured into the abalone shells to be gently stirred before being ready for application.

According to Henshilwood, this complex process, involving several components that had to be sourced from different places, indicates that humans 100,000 years ago had an elementary understanding of chemistry and the ability for long-term planning.

Investment of time and energy

“Archaeologists are always looking for signatures of symbolism and the beginnings of modern behaviour, and we’re fixed on ochre as an indication of art and other symbolic productions,” said Peter Hiscock from the Australian National University in Canberra, who was not involved in the research.

“What’s interesting about this is the scale of ochre processing. The date is not so surprising, because we’ve found earlier hints, but this indicates that there’s a whole craft of production in place here.”

Hiscock added that sites from the Middle Stone Age are comparatively rare in the archaeological record, so it follows that if this workshop was an incredibly rare type of site, it’s unlikely that it would have been uncovered. “This is sufficiently common, if we’re finding it,” he said.

“What it signals is an intense vocation of ochre use that obviously became very common. We’re seeing all these discoveries [of ochre use], so this vocation must have intensified in the sense that people are really investing their time and energy in procuring the ochre, collecting the objects [for processing] and so on.”


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