Skip to comments.Early Human Lessons: Hot Rocks Make Sharper Tools
Posted on 08/13/2009 6:28:59 PM PDT by BGHater
So, it's the southern tip of Africa, about 70,000 years ago, and some humans have built a fire. Maybe it's to keep warm, or to cook up some gazelle steaks. To kill time, they do a little flint knapping whacking one rock with another to chip off razor-sharp flakes. They use the flakes to cut meat or make spear points.
After the fire dies down, someone drags a big stone out of the embers and tries whacking that, and discovers that it makes really good flakes: it chips predictably and the flakes are symmetrical and sharp.
Eureka pyroengineering is born. "It's a real critical step in the evolution of technology," says Kyle Brown, a graduate student in archaeology at the University of Cape Town in South Africa. "Somewhere around 70,000 years ago it became very common."
The campfire scenario is based on Brown's own eureka moment.
Here's how it happened. Brown had noticed that many ancient tools found in South Africa were made from silcrete, a kind of rock notoriously difficult to work with. It's known that heating rock can improve stone for making tools, but it's thought to have been a more modern discovery; no one knew when or where the practice started.
So Brown tried heating some silcrete rocks himself, for 10 hours at a time.
"I did a lot of the early experiments with a fire pit in my yard," he recalls, "just sitting up making sure that the fire stayed hot and had enough wood on it."
His neighbors thought he was crazy. But Brown discovered that cooked rock was much easier to flake. "The stone becomes harder and stiffer," Brown says, "it basically becomes more brittle, which is great if you are breaking something you want it to break more easily."
The flakes were sharper too and they had a certain glossiness on the surface that the 70,000-year-old stone tools also had.
Writing in the journal Science, Brown says early humans must have done this intentionally. He doesn't think the flakes were made first and then dropped into a fire; he tried that and it didn't work. Further tests suggested that cooking the rock first, to about 600 degrees Fahrenheit, apparently alters its crystalline structure and gives it something knappers call "rebound hardness" so it will fracture more predictably.
Anthropologist Grant McCall from Tulane University, who studies and makes stone tools himself, says it seems to be part of the flowering of what scientists call "behavioral modernity" things that modern humans did that set them apart from their ancestors.
"The striking ones from elsewhere in southern Africa have to do with the manufacture of symbolic objects," he says. "So you have the manufacture of marine shell beads or engraved ochre fragments... that indicate that people were operating in a very symbolic way and that they possessed modern language in the way that modern humans do today."
This explosion of modern behavior including pyroengineering tools seems to have occurred earlier in southern Africa than in Europe or Asia. And it's possible pyroengineering began even further back. The scientific team has found the same kind of tools at other South African sites that appear to date back 165,000 years. That's long before so-called "modern" behavior emerged elsewhere, making the discovery even more... striking.
Early humans may have used cooking methods to transform silcrete (left) into sharp tools (right). And the ability to heat and carve rocks into tools shows they were thinking in complex and symbolic ways.
Deep down in layers of rock, paleoanthropologists dig up clues to ancient toolmaking.
The southern tip of Africa was home to the first human masters of fire, say paleoanthropologists. Their discovery of silcrete tools in ancient campsites has pushed hypothetical origins of pyrotechnology up at least 20,000 years in time.
OOA and Fire ping.
So we’ve finally moved beyond Douglas Adam’s exhortation to “keep banging the rocks together!”
What, no mention of “the obelisk”?
Is this an article about the Fox News Babes? Oh...my bad.
Old news. Heat treating makes for sharper, easier to flake, and usually more colorful tools but it also makes the material brittle, so it is not suitable for all tools.
Thanks BGHater for the ping and thanks decimon for the topic. :')
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· The Archaeology Channel · Excerpt, or Link only? · cgk's list of ping lists ·
Whoops! I take a couple of days off, and I have to be retrained!
Thanks BGHater for the topic as well as the ping. I had this one open in the adjacent tab, and got confused. Time for a vitamin water...
Evidence for Use of Fire Found at Peking Man Site
CRIENGLISH.com | Aug 11, 2009 | Unknown
Posted on 08/12/2009 12:16:08 PM PDT by decimon
Why are scientists routinely surprised when they discover that people who only had rocks, dirt, wood, plants, fungi, grasses and animal by-products found ways to use them that we, who don’t rely on these things, can imagine.
... Im one of those elusive guys that makes obsidian scalpels and would like to say a few words about them. Firstly, Ive been making them for a number of years now and can tell you that they ARE all theyre cracked up to be and more no kidding theyre sharp ultra-sharp. I make them to order, so each lot is a customized job for each customer and all made to the customers specifications. Each and every one of them is handmade using a technique called pressure flaking and I go to extremes to protect that edge as the blade is detatched from the core. As you can probably well imagine, I do not, nor will I ever mass produce them its a matter of quality over quantity.
Now about the blades. Like I said theyre ultra-sharp and Ill put them up against anything on the market. Coupled with that, theyre exceptionally delicate and have to be handled with care. They will not tolerate lateral pressure, but when used properly will perform flawlessly. They should only be used on soft tissue period.
Since I work with this material, I have been cut from time to time and by all rights ought to look like Ive been sorting out a bobcat fight, but thats not at all the case. I can safely say that every cut I ever suffered from an obsidian blade healed without any scaring whatsoever. It sounds amazing, but the cuts are so clean thats the way they heal.
For whatever reason, these blades arent approved by the FDA and this baffles the daylights out of me too. Nevertheless they are being used with great success (albeit in limited numbers and only by a handful of surgeons and researchers).
Sometimes rocks crack in fire - and it could have been noticed they produced sharp corners.
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