Month: February 2024

Neanderthals and the earliest ‘plastic’ handles

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February 2024 was a notable month for discoveries about ancient technology: first that of an ancient tool probably used in rope making and now signs of the use of a composite ‘plastic’ material in stone-tool hafts. Both are from Neanderthal sites in France, the first dated around 52 to 41 ka and the second in the Le Moustier rock shelters of the Dordogne – the type locality for the Mousterian culture associated with Neanderthals (Schmidt, P. et al. 2024. Ochre-based compound adhesives at the Mousterian type-site document complex cognition and high investment. Science Advances, v. 10, article ead10822; DOI: 10.1126/sciadv.adl0822), dated at around 56 to 40 ka. The second discovery resulted from the first detailed analysis of unstudied artifacts unearthed from Le Moustier in 1907 by Swiss archaeologist Otto Hauser that had been tucked away in a Berlin Museum.

Patrick Schmidt of the University of Tubingen in Germany and colleagues  from Germany, the US and Kazakhstan identified stone artifacts that show traces of red and yellow colorants. At first sight it could be suggested that they are decorations of some kind. However, they coat only parts of the stone flakes and are sharply distinct from the fresh rock surface and the sharpest edges. Another feature discovered during chemical analysis is that the colour is due to iron hydroxides (goethite) but this ochre is mixed with natural bitumen: the coating is a composite of an adhesive and filler not far different from what can be purchased in any hardware store.

LEFT: Stone flake from the Le Moustier site in France, partly coated with a reddish iron-rich colorant. RIGHT: Experimental stone flakes with 55:44 mix of goethite and bitumen (top) and pure bitumen (bottom) being handled. (Credit: Schmidt et al. Figs 1A, 3).

The authors tested the properties of the mixtures against those of bitumen alone – an adhesive known to have been used along with various tree resins to haft blades to spears in earlier times. In particular they examined the results of ‘cooking’ the substances. Whether unheated or ‘cooked’ a mixture of ochre and bitumen is up to three times stronger than pure bitumen. A further advantage is that the mixed ingredients are not sticky when cooked and cooled, whereas bitumen remains sticky, as the illustration clearly shows. Anyone who has handled a stone blade realises how sharp they are, and not just around the cutting edges. So Schmidt and colleagues tried to use the composite material as a protective handle when stone flake tools were gripped for cutting or carving. The composite handles worked well on scrapers and blades, even in the softer, ‘uncooked’ form

Similar composite adhesives are known from older sites in Africa associated with anatomically modern humans, but not for this particular, very practical use. It is perhaps possible that the use of bitumen mixed with ochre was brought into Europe by AMH migrants and adopted by Neanderthals who came into contact with them. Yet the limestones of the Dordogne valley yield both bitumen in liquid and solid forms, and ochers are easily found because of their striking colours. Long exposure of petroleum seeps drives off lighter petroleum compounds to leave solid residues that can be melted easily to tarry consistency. So there is every reason to believe that Neanderthals developed this technology unaided. As Schmidt has commented, “Compound adhesives are considered to be among the first expressions of the modern cognitive processes that are still active today”.

Changing Atlantic Ocean currents may threaten Gulf Stream warming of Europe

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Climate during the last Ice Age was continually erratic. Generally fine-grained muds cored from the floor of the North Atlantic Ocean show repeated occurrences of layers containing gravelly debris. These have been ascribed to periods when ice sheets on Greenland and Scandinavia calved icebergs at an exceptionally fast rate, to release coarse debris as they melted while drifting to lower latitudes. These ‘iceberg armadas’ (known as Heinrich events) left their unmistakable signs as far south as Portugal. Their timing correlates with short-lived (1 to 2 ka) warming-cooling episodes (Dansgaard-Oeschger events) recorded in Greenland ice cores that involved variations in air temperature of up to 15°C. The process that resulted in these sudden climate shifts seems to have been changing ocean circulation brought about by vast amounts of fresh water flooding into the Arctic and North Atlantic Oceans. This lowered seawater density to the extent that its upper parts could not sink when cooled. It is this thermohaline circulation that drags warmer surface water northwards, known as the Atlantic Meridional Overturning Circulation (AMOC), part of which is the Gulf Stream. When it fails or slows the result is plummeting temperatures at high latitudes. The last major AMOC shutdown was after 8 ka of warming that followed the last glacial maximum. Between 12.9 and 11.7 ka major glaciers grew again north of about 50°N in the period known as the Younger Dryas, almost certainly in the aftermath of a flood to the Arctic Ocean of glacial meltwater from the Canadian Shield. Around 8.2 thousand years ago human re-colonisation of Northern Europe was set back by a similar but lesser cooling event.

The Atlantic Meridional Overturning Circulation (AMOC). Red – warm surface currents; cyan – cold deep-water flow. (Credit: Stefano Crivellari)

Three researchers at Utrecht University, the Netherlands have issued an early warning that the AMOC may have reached a critical condition (Van Westen, R.M., Kliphuis, M & Dijkstra, H.A. 2024. Physics-based early warning signal shows that AMOC is on tipping course. Science Advances, v. 10, article adl1189; DOI: 10.1126/sciadv.adk1189). Previous modelling of AMOC has suggested that only rapid, massive decreases in the salinity of North Atlantic surface water near the Arctic Circle could shut down the Gulf Stream in the manner of Younger Dryas and Dansgaard-Oeschger events. René van Westen and colleagues have simulated the effects of steady, long-term addition of fresh water from melting of the Greenland ice sheet. They ran a sophisticated Earth System model for six months on the Netherlands’ Snellius super computer. Their model used a slowly increasing influx of glacial meltwater to the Atlantic at high northern latitudes.

The various feedbacks in the model eventually shut down the AMOC, predicted to result in cooling of NW Europe by 10 to 15 °C in a matter of a few decades. Yet to achieve that required the model to simulate more than 2000 years of change. It took 1760 years for a persistent AMOC transport of 10 to 15 million m3 s-1 to drop over a century or so and reach near-zero. That collapse involved around 80 times more melting of Greenland’s ice sheet than at present. Yet their modelling does not take into account global warming: including that factor would have exceeded their budgeted supercomputer time by a long way. Melting of the Greenland ice sheet is, however, accelerating dramatically

Van Westen et al. have shown the possibility that steadily increasing ice-sheet melting can, theoretically, ’flip’  the huge current system associated with the Atlantic Ocean, and with it regional climate patterns. The tangible fear today is of a more than 1.5°C increase in global surface temperature, yet a warming-induced failure of AMOC may cause local annual temperatures to fall by up to ten times that. Rather than the currently heralded disappearance of sea-ice from the Arctic Ocean, it may spread in winter to as far south as the North Sea. The only way of forecasting in detail what may actually happen – and where – is ever-more sophisticated and costly modelling of ocean currents and ice melting in a warming world. Uncertain as it stands, the work by van Westen and colleagues may well be ignored: perhaps as a ‘thing we dinnae care to speak aboot’.

See also: Le Page, M. 2024. Atlantic current shutdown is a real danger, suggests simulation. New Scientist, 9 February 2024; Watts, J. 2024. Atlantic Ocean circulation nearing ‘devastating’ tipping point, study finds. The Guardian, 9 February 2024.

Earliest evidence for rope making: a sophisticated tool

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Even at my age, if I rummage through pockets of various bits of outdoor clothing there’s a good chance I’ll find a handy length of string that I have scavenged at some time. It’s a just-in-case thing, which I learned from my father and grandad. One can hardly imagine a hunter-gatherer not having string or lengths of sinew for that very reason. Cordage has many other uses than merely securing something: bags, mats, nets, snares, fabric, baskets, huts made of sticks and fronds, and even watercraft. Yet archaeological evidence for twine is exceedingly rare. The oldest known string – made of bark fibres – was found wrapped around a stone tool at a 52 to 41 ka Neanderthal site in the Rhône valley 120 km north-west of Marseille. Rope is somewhat more difficult to make as it requires twisting together several lengths of simpler cordage. Once that skill is cracked a rope maker is on the verge of engineering!

The reassembled rope-making tool from Hohle Fels Cave (Credit: Conard & Rots, Fig 2)

In 2015 archaeologists unearthed several pieces of worked mammoth ivory from the Hohle Fels Cave in SW Germany. They were dated to between 40 to 35 ka and associated with Aurignacian stone tools made by modern humans. Fifteen pieces could be fitted together to yield a 20 cm long ‘baton’. First believed to be some kind of ritual object, the fact that 4 circular holes had been bored through the ‘baton’ suggested it must have had some practical use, perhaps for straightening wooden shafts. Then it became clear that each hole was surrounded by spirals of carefully carved, V-shaped notches. Nicholas Conard and Veerle Rots of the University of Tubingen realised that the object may have been used for making rope using a technique known from the Egyptian pharaonic period into medieval times (Conard, N.J. & Rots, V. 2024. Rope making in the Aurignacian of Central Europe more than 35,000 years ago. Science Advances, v. 10, article adh5217; DOI: 10.1126/sciadv.adh5217).

Frame from a movie showing how the tool may have been used to make ropes. The three ‘feeders’ twist foliage clockwise whereas the fourth pulls and imparts an anticlockwise twist to the three stands. (Credit: Conard & Rots, Supplementary material, Fig S15)

After a little practice, four people were able to make sturdy rope using a replica of the tool. Three twisted together fibrous materials, such as the stems and leaves of bulrushes (Typha), and pushed the rough cordage through the intact holes. A fourth person pulled the cordage through and counter-twisted the three strands into rope about 1.5 cm thick – thicker rope would also have required a tool with more holes and more operators. The spiral grooves maintained the initial clockwise rotation of each strand of cordage, so that when all three were twisted together in an anticlockwise sense the counter rotation held the rope together firmly. Remarkably, the small team were able to produce 5 m of rope in 10 minutes. Other common kinds of fibrous plant material, such as linden and willow were used successfully. Incidentally, the tool squeezed edible starch from the foliage of bulrushes. But it seems that this particular rope-making took only performed well for coarse materials. Making rope from finer firbres, such as animal sinew, nettle, flax and hemp would probably have required another design with smaller holes.

A movie of the manufacturing process can be downloaded.