New studies in South Africa examine early stone tools to suggest that ancient humans did choose stones according to rock properties, rather than solely accessibility.
What was the first science in history? Astronomers, biologists, mathematicians, chemists, and physicists each have their preferred answer to this question. But the studies and stories shared in this edition of Core Elements indicate that geology was probably the first science, and our stone-tool-making ancestors were the first geologists.
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Rasoul Sorkhabi
Editor, Core Elements
Selecting Stones for Early Tools in South Africa
Photo by Food Impressions/Shutterstock.com
A recent paper at the Proceedings of National Academy of Sciences investigates stone tools found at an archaeological site in South Africa and infers that ancient humans selected and utilized these tools with some knowledge of rock type and properties.
The site:
Diepkloof Rock Shelter is located in Western Cape, South Africa with archeological materials dating back 129,000 years (Late Pleistocene).
The site was first excavated in 1973.
This year, it was recognized as a World Heritage Site by UNESCO.
The people and stones: Researchers studied stone tools used by two different communities of Middle Stone Age:
The Still Bay community, which existed some 71,000 years ago
The Howiesons Poort community, which existed about 65,000 years ago
The major type of rocks at Diepkloof are hydrothermal quartz, quartzite, hornfels, and silcrete.
New study: Researchers from the University of Tübingen collected eight samples from each of the rock types at Diepkloof and measured each sample’s mechanical properties, including density, fracture toughness, elastic or Young’s modulus, Vickers hardness, strength, and Weibull modulus (fracture variability).
These data were compared to stone tools from Diepkloof to understand how ancient peoples selected rocks for toolmaking.
Findings:
The Diepkloof inhabitants tested various rocks available to them but selected specific rock types for tools.
In addition to material availability and accessibility, ancient humans seem to have also considered fracture behavior, workability, and other properties of stone during toolmaking.
For example, hornfels were the least-used option for stone tools, because this rock’s fracture behavior is the least-predictable during knapping.
The Still Boy occupants used mainly coarse-grained quartzite from the site’s shelter wall.
This metamorphosed sandstone is hard and fractures well. It has the most homogenous fracture behavior (indicated by highest Weibull modulus).
Still Boy points are long, double-edged points likely used as spear tips and for cutting.
Quartzite accounted for 71 percent of bifacial stone tools.
The later Howiesons Poort community preferred fine-grained silcrete, an indurated soil layer cemented by silica, for stone tools.
These inhabitants made small blades for arrowheads, spearpoints, and backed stones tools.
Silcrete accounted for 69 percent of all blades and bladelets.
Some of the silcrete tool stones were transported from areas up to 70km away from Diepkloof.
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In an article in GSA Today, Jon Spencer of the University of Arizona discusses how the use of stone tools by hominins was probably responsible for the rapid rate of evolutionary brain growth also known as encephalization.
Definition: Encephalization is the measure of brain size relative to body size for a given species.
The great brain gain: As we go back in time, it is difficult to precisely differentiate hominins (human lineage species) and hominids (ape-lineage species, including humans).
The oldest fossils of “hominins” Sahelanthropus tchadensis (7 Ma), Ardipithecus ramidus (4.4 Ma), and Australopithecus anamensis (4.2 Ma) have endocranial (“inside the skull”) volumes similar to that of chimpanzees.
Beginning at about 3.5 Ma, rapid encephalization of humans took place and continued all the way until the emergence of homo sapiens.
Spencer estimates that this “great acceleration” of brain volume was 4.2 percent per 100,000 years, or about 0.001 percent per generation.
Rapid encephalization was associated with several changes including:
Use of spears for hunting and defense
Use of sticks for digging
Discovery of fire for cooking
Development of stronger and more dexterous thumbs
Invention of language
Development of complex social relationships and community size
Spencer suggests that while all these factors have been influential, “stone tools appear to have been foundational in triggering 3.5 m.y. of rapid evolutionary brain growth.”
Oldest stone tools ever found:
By 3.4 Ma, hominins used stone tools to butcher animals as is evidenced by animal bones with scrapes and cut marks.
The oldest stone tools—probably used for chopping and crushing—date back 3.3 Ma. These tools were found on the west side of Lake Turkana in Kenya and are basaltic rocks.
The Oldtown stone tools, named for Tanzania’s Olduvai Gorge, are very abundant and have been dated between 2.6 and 1.6 Ma. They were first recognized by Louis Leakey in the 1930s.
Why it matters:
Human evolution and use of stone tools took place in East Africa.
This region is an active continental rift system that has produced large volumes of basalts and volcanic glasses (obsidian).
Thank you all for submitting your answers to our weekly quiz!As a reminder, the question asked was:Define, and give examples of, the difference between terrain and terrane?
There were several great and correct responses. I’ll share one here:
“Terrain is the topographic manifestation in an area: Hills, valleys, rivers, mountains etc. Terrane refers more to a geologic province: Basin and range, high-altitude plateau, fold and thrust belt, Deccan Traps, or large igneous province”—Brian Horn
I will add that the distinction between “terrain” and “terrane” became prominent in the 1970s when geologists discovered that the northwestern part of the North American Cordillera (the Pacific Northwest) was a mosaic of different “terranes” accreted over tens of millions of years. In this new definition, a terrane is a fault-bounded continental fragment with a distinct geologic history and rock formations.
Now, here’s the question for this week:
What is the difference between Early Jurassic and Lower Jurassic or Late Cretaceous and Upper Cretaceous? Give examples of how you would use these terms.
Please email your response by October 3 to editorial@aapg.org (subject line: Core Elements Quiz) for a chance to be featured in next week's edition!
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