Tuesday, August 18, 2009

75,000 years of Fired Tools

The antiquity of the use of fire by our hominid ancestors is truly astonishing and plausible evidence as quoted here is for 800,000 years. That is certainly ample enough to allow mankind to lose the robust jaw bones needed to rend meat of a bone and generally change out to modern dentition. That also allowed for the development of an enlarged brain case as part of a protracted juvenile phase.

The question of tool use was much trickier and had to surpass the obvious use of a stick and hand stone any primate might use. I had already surmised in my manuscript several years ago using scant evidence that the likely transition time was at least 70,000 years ago. Here we have specific confirmation that that was in fact true.

I also proposed a development niche that sped this development prior to this particular evolution of full tool use. That probably lasted for much of the preceding 100,000 or so years and both developed tool use and large social groupings, both unique to humanity.

Once this level of tool use and tool modification arose, then largely fully modern man spread out into every available valley and island on Earth. Some cut off populations still reflect that ancestry, but even they are fully modern humanity.

This aggressive socially organized hunting machine swept aside any competitors and dominated several niches and has also created many unique additional niches.

This clearly pins down the time of true emergence as around 75,000 years ago. The expanding population would have penetrated everywhere inside of a couple of thousands of years in the old world. We now know that this also likely include Australia.

The Americas were still much later but still plausibly as soon as 40,000 years ago and certainly no later than around 20,000 thousand years ago.

This starts off with a report from LiveScience and then we have the original release from Arizona State

Fire Used to Make Better Tools 75,000 Years Ago

Clara Moskowitz, LiveScience Staff Writer

posted: 13 August 2009 02:04 pm ET


Fire pit and sand both used for heat treatment experiments. Silcrete is placed beneath a layer of sand and then a fire is built over the top. The temperature is gradually increased and then slowly decreased to avoid cracking the stone. Credit: © Science/AAAS

Experimentally replicated blade tools produced with heat treated silcrete. Some of these tools may have been mounted unto a wood handle to create a tool with disposable blades, as pictured above. Credit: © Science/AAAS

Early humans crossed a threshold around 75,000 years ago, when they started painting symbols, carving patterns and
making jewelry. A new study found they also began to use fire to make tools around that time.

Until now, this complex, multi-step process for tool making was only known to occur as recently as 25,000 years ago in Europe. But the new findings show this breakthrough occurred much earlier,
and in Africa, not Europe.

By heating up stones in a fire before chipping away at them to make blades, early humans could make tools sharper and produce them more efficiently.

Scientists think this advancement represents a link between the earlier use of
fire for cooking and warmth, and the later production of ceramics and metals.

"Around 800,000 years ago we see some of the first evidence for hominid controlled use of fire," said study leader Kyle Brown, a graduate student in archaeology at the University of Cape Town in South Africa and at Arizona State University. "And then at about 10,000 years ago we see evidence for production of ceramics. And at about 5,000 years ago we see metal working."

"The heat treatment of tools is sort of a bridging technology," he said.

The development of this skill may represent a level of
complex cognition that was just beginning in humans at this time.

Brown and colleagues discovered the remains of tools that had been made using fire at archaeological sites in South Africa. The tools were made out of a stone called silcrete. Some of the earliest examples could date back to 164,000 years ago, and the researchers found that by 72,000 years ago this technique was seemingly common for silcrete tools.

The heat-treated tools look almost like stone razor blades, and are small enough that they could have been set into a handle.

"It’s a big debate to figure out what people were doing with these things," Brown told LiveScience.

"Some people argue that they are the first arrowheads. Other people argue that they were set in a handle and used as knives."

To make the tools, early humans would have had to bury the stone beneath a fire, then slowly heat it up, keep it at a high temperature for hours, and then let it cool. The process was complicated and could take one to two days of continuous heating.

The heat transforms the stone so that it's harder and more brittle, which allows it to be more easily chipped away into a sharper edge. It also gives the stone a special sheen, which helped the archaeologists identify the tools as resulting from fire treatment.

"The most noticeable thing about heat-treated stone is that it has a luster or a gloss to it that’s fairly distinctive," Brown said. "A stone that's heated will only show that gloss if it's been flaked after it's heated."

The researchers then confirmed that the tools had been warmed in a fire with a technique called archaeomagnetics, which measures the realignment of iron particles in stone that results from heating. Another chemical process called thermoluminescence provided further proof that the stones had been heated.


Early modern humans use fire to engineer tools


Evidence reported in the Aug. 14 issue of the journal Science shows that early humans living on the southern coast of Africa 72,000 years ago used a complex heat treatment process to manufacture blades and bifacial tools. Unheated silcrete (left) can show dramatic changes in color and texture after heating and flaking (right). An international team, including three researchers from the Institute of Human Origins at Arizona State University, note that silcrete is not found closer than 5 kilometers from their excavation at Pinnacle Point, Mossel Bay, South Africa, and that most pieces found are extensively flaked. (Photo by Kyle Brown/South African Coast Paleoclimate, Paleoenvironment, Paleoecology, Paleoanthropology Project)

Discovery places complex cognition at 72,000 years ago, and perhaps far earlier

Evidence that early modern humans living on the coast of the far southern tip of Africa 72,000 years ago employed pyrotechnology – the controlled use of fire – to increase the quality and efficiency of their stone tool manufacturing process, is being reported in the Aug. 14 issue of the journal Science. An international team of researchers, including three from the Institute of Human Origins at Arizona State University, deduce that "this technology required a novel association between fire, its heat, and a structural change in stone with consequent flaking benefits." Further, their findings ignite the notion of complex cognition in these early engineers.

"Our illumination of the heat treatment process shows that these early modern humans commanded fire in a nuanced and sophisticated manner," says Kyle Brown, the lead author and a doctoral candidate at the University of Cape Town, and field and lab director in Mossel Bay, South Africa, for ASU's Institute of Human Origins.

"We show that early modern humans at 72,000 years ago, and perhaps as early as 164,000 years ago in coastal South Africa, were using carefully controlled hearths in a complex process to heat stone and change its properties, the process known as heat treatment," Brown says.

"Heat treatment technology begins with a genius moment – someone discovers that heating stone makes it easier to flake," says Curtis Marean, the project director and a co-author on the paper. Marean is a paleoanthropologist with the Institute of Human Origins and a professor in the School of Human Evolution and Social Change at Arizona State University's College of Liberal Arts and Sciences.

"This knowledge is then passed on, and in a way unique to humans, the technology is slowly ratcheted up in complexity as the control of the heating process, cooling and flaking grows in sophistication," Marean says.

This creates a long-chain technological process that the researchers explain requires a complex cognition, and probably language, to learn and teach.

The heating transformed a stone called silcrete, which was rather poor for tool making, into an outstanding raw material that allowed the modern humans to make highly advanced tools.

The eureka moment

The focus of Brown's research involves experimentally replicating the types of tools and production debris found at African archaeological sites to understand how and why people made and used these tools.

"In numerous field surveys with co-author David Roberts, who is a leading expert on silcrete formation, we were unable to locate stone outcrops with material that matched the fine-grained texture and often reddish color of the silcrete artifacts we excavated at Pinnacle Point," Brown says. "The silcrete we had collected was just not suitable for tool production."

Most of the silcrete they found was intensively flaked. It was unusual to find a piece larger than a few centimeters. However, one day in 2007, while Brown and Marean were at the Pinnacle Point Site 5-6 (PP5-6) they found a huge flake of silcrete embedded in ash – the largest piece of silcrete they had ever seen on an archaeological site, nearly 10 centimeters in diameter.

"It looked like it had been accidentally lost in a fire pit," Brown says. He recalls how many of the silcrete tools from the site had a sheen or gloss that reminded him of tools he had examined in North American collections that were heat-treated.

"That is when we developed the heat treatment idea," Marean says. "The co-association of the ash cemented to the silcrete, the red color of the silcrete, and its inexplicably large size was the genesis conditions of our eureka moment."

To test their theory, Brown placed some of the silcrete stone beneath their fire pit one evening, building a hot fire over the top.

"When I returned to dig the stone out the following day, the results were amazing. After heating, the silcrete became a deep red color and was easily flaked. Most importantly, it looked exactly like silcrete from site PP5-6. Using heated silcrete we were then able to produce realistic copies of the actual silcrete tools," Brown says.

Barbequing rocks

"Here are the beginnings of fire and engineering, the origins of pyrotechnology, and the bridge to more recent ceramic and metal technology," Brown says.

According to Marean, the silcrete bifaces are re-usable tools with many potential functions: effective hunting weapons, excellent knives and items of value for exchange.

"This explains why people would invest so much effort at wood collection and heat treatment for their production," Marean says.

And, the hearths used to test their theory "were designed to mimic what people in the past may have done. So, not only did we heat silcrete, but we barbecued (a ‘braai' in South Africa) steaks and chops at the same time as measuring the temperature profiles with our thermocouple," Marean says.

Symbolic behavior and modern human origins

"Our discovery shows that these early modern humans had this complex cognition," Brown says. "This expression of cognitive complexity in technology by these early modern humans on the south coast of South Africa provides further evidence that this locality may have been the origin location for the lineage that leads to all modern humans, which appeared between 100,000 and 200,000 years ago in Africa," Marean says.

"There is no consensus as to when modern human behavior appears, but by 70,000 years ago there is good evidence for symbolic behavior," he says. "Many researchers are looking for technological proxies for complex cognition, and heat treatment is likely one such proxy.

"Prior to our work, heat treatment was widely regarded as first occurring in Europe at about 25,000 years ago," Marean says. "We push this back at least 45,000 years, and, perhaps, 139,000 years, and place it on the southern tip of Africa at Pinnacle Point."

The African location was at the center of another discovery by Marean – the documentation of the earliest evidence for exploitation of marine foods and modification of pigments - reported in the Oct. 17, 2007, journal Nature.

"Combined, these results sharply advance our knowledge of modern human origins, and show that something special in human cognition was happening on the coastline of South Africa during this crucial final phase in human origins," Marean says.

He adds that some time around 50,000 to 60,000 years ago, "these modern humans left the warm confines of Africa and penetrated into the colder glacial environment of Europe and Asia, where they encountered Neanderthals.

"By 35,000 years ago these Neanderthal populations were mostly extinct, and modern humans dominated the land from Spain to China to Australia," Marean says.

"The command of fire, documented by our study of heat treatment, provides us with a potential explanation for the rapid migration of these Africans across glacial Eurasia - they were masters of fire and heat and stone, a crucial advantage as these tropical people penetrated the cold lands of the Neanderthal," says Marean.

NSF, others fund SACP4

Other members of the research team and co-authors of "Fire As an Engineering tool of Early Modern Humans," include David Baun, University of Cape Town; Andy I.R. Herries, University of New South Wales and University of Liverpool; Zenobia Jacobs and Michael C. Meyer, University of Wollongong, Australia; Changal Tribolo, CNRS-University of Bordeaux, France; David L. Roberts, Council for Geoscience, Republic of South Africa; and Jocelyn Bernatchez, Institute of Human Origins, ASU.

They work together on the South African Coast Paleoclimate, Paleoenvironment, Paleoecology, Paleoanthropology Project, known as SACP4, which is directed by Marean, funded by the
National Science Foundation and the Hyde Family Foundation, and supported by Arizona State University research and academic units including the Institute of Human Origins, Institute for Social Science Research, and School of Human Evolution and Social Change in the College of Liberal Arts and Sciences.

"Our team, working at Pinnacle Point near Mossel Bay, is a leader in revealing the process of how we became who we are today, and we are doing this with state-of-the-art fieldwork and laboratory analysis at this locality," Marean says.

He notes the specifics of the discovery involved combining thermoluminescence, magnetic analysis, optically stimulated luminescence dating, experimental stone tool production, mechanical testing, and field archaeology.

Carol Hughes,


College of Liberal Arts and Sciences

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