Low-velocity spatter from the Neandertal palette

Paleolithic archaeology is the home of some of the best forensic work anywhere. I've often written about impressive analyses of stable isotopes, microscopic starch grains, phytoliths, and wear traces on artifacts. Among these, some of the most detailed studies involve the use of pigments by ancient people. Out of these, last week's paper by Wil Roebroeks and colleagues Roebroeks:ochre:2012 really stands out by wringing every drop of information out of an ancient archaeological horizon.

I wrote last fall about the pigment "workshop" at Blombos, South Africa, which is around 100,000 years old ("Blombos pigment workshop"). And some time ago I wrote extensively about pigment use among Mousterian-era Neandertals ("Pigment use and symbolic behavior in the Neandertals"). These kinds of studies face many challenges. If a mineral pigment has been used by ancient people, it will often exist in a site only in tiny pieces. At best, some accumulation of the mineral pigment might give an indication of intentional use by ancient people. In this case, the material was scattered in a dozen or so tiny droplets over a diameter of 15 meters.

Mineral pigments have uses other than decoration. Sometimes they were used as part of a formula to make glue, which we can find still adhering to the back end of stone points. Ochre may also have been used in the process of softening animal hides. These uses were reviewed by Lyn Wadley Wadley:replication:2005, who has done more than anyone to uncover the ways MSA people processed ochre in South Africa. Pigments were used by humans as early as 200,000 years ago in Africa, and earlier than 100,000 years ago in West Asia (Skhul and Qafzeh dErrico:Skhul:2010) and Europe.

The new study by Roebroeks and colleagues extends the time of pigment use in Europe to earlier than 200-250,000 years ago, which is newsworthy. It is notable that this time is early enough to suggest that the common ancestral population of European and African archaic humans may have also used pigment (or have been capable of learning to use it given the right cultural or ecological conditions). But to me, much more interesting is the way the red ochre was discovered in the archaeological site, and the experimental replication of the process by which it was deposited.

In the course of the archeological excavations, one of the sites, site C (excavated between 1981 and 1983), yielded 15 small concentrates of red material, with maximum size of 0.20.9 cm and 0.10.3 cm thick, with sharp boundaries to the sedimentary matrix (Figs. 1 and 2). The contrast in color between the bright- red concentrates and the yellowish-brown (Munsell soil color 2.5Y5/3) to grayish-olive (5Y5/3) sediment was striking (Fig. 2), facilitating recovery of these small, friable pieces at this site, excavated over an area of 264 m2 (Fig. 3). Although the red material has been interpreted as hematite (15, 23), these finds did not play a role in the history of ochre use, even though Maastricht-Belvdre became one of the flagship sites of Middle Paleolithic archeology, reviewed extensively in numerous textbooks (24).

These hematite features are pictured in several ways in the article and supplement. They are tiny: here is one of them, on a piece of sediment that was removed in total from the site:

Red ochre droplet from Roebroeks et al 2012 supplement

Detail of Figure S4 from Roebroeks et al. 2012 supplement, showing red hematite concentration upon sediment fragment removed from site.

It is simply remarkable to me that this excavation in the early 1980s uncovered an ancient sediment horizon using such great care that these tiny patches of red ochre were found. All were only a few millimeters in size. They were highly visible against the surrounding sediment, which helps to confirm that they don't belong there. Other aspects of the archaeology were likewise carried out meticulously. For example, the paper presents two refits of flakes and cores taken from the site, demonstrating that primary reduction of stone artifacts happened there with some products taken away from the site.

The paper notes the lack of hematite in local contexts where people might have found it, arguing that it must have been imported from a distance of at least 40 km from a natural source. The archaeological presence of contemporary tools taken in the opposite direction toward that hematite source helps support this argument. Forty kilometers isn't terribly far for hunter-gatherers, but it is interesting.

The experimental aspect of the paper is only sketched out in the text, and is described much more fully and illustrated in the supplement. Roebroeks and colleagues, looking at the small patches scattered across a diameter of 15 meters, guessed that they were a low-velocity spatter dropped from some kind of liquid. So they set out to reproduce it:

We hypothesize that the best explanation is that the fine hematite material was originally concentrated in a liquid solution, and that blobs of this ochre-rich substance became embedded in the sediments during use of the liquid,spilled on the soil surface. To test this interpretation, we performed an experiment to observe the impact of drops of a hematite-rich liquid on the site C sediment (SI Text). Despite the limitations of this experiment, the similarity of the experimentally produced concentrates to the archeological concentrates at both macroscopic and microscopic levels is remarkable (SI Text) and lend support to our interpretation of how the material entered the sediment.

The experiments are illustrated very nicely in the supplementary information for the paper. Here's one of the photos:

Red ochre droplet experiment, figure S10, B from Roebroeks et al 2012

Figure S10b from the supplement of Roebroeks et al. 2012. Original caption: "(A and B) Experimental hematite dots created on a 'smoothed' dry surface (50-cm height, 0.3-cm drops). The concentrates are within small craters produced during impact of the drops on the dry sediment."

Their "hematite liquid" consisted of ground mineral combined with rainwater, "launched" from a height of a half meter. Sounds like something that should be for sale in a natural cosmetics store.

What were these ancient people doing with liquid ochre? Good question. Given the unique care of excavation, the local context in which the mineral is highly visible in the fine sediment, I wonder how many other instances of similar deposits may have been lost over the years. It is sometimes excruciating to wait for results from an archaeological discovery, but the extremely slow and careful excavation methods do obtain results that could not be gotten any other way.

I was privileged to see some details from another excavation this week, where even greater care is being taken. It's totally remarkable some of the things that are out there waiting to be found.