Sparks and Stone Tools
I am still hung-up on the earlier posts in this thread, regarding whether the sparks from impacted stones can reliably initiate combustion. Someone earlier had pointed out the effect of piezo-electric qualities of crystaline SiO2 (megacrystalline quartz), but I doubt that the thermic effect of impacting quartz on quartz is enough to produce the combustion temp required for cellulose. Nor is the spark burn-time long enough to transmit enough heat to the tinder. The reason that sparks caused by metal-on-metal impact can cause fires is because the metal flakes are being slowly oxidized by the air, providing more time to transmit the heat to the tinder on which the spark lands. Also, the exothermic output of oxidizing iron is much greater than the thermic output of impacted silicon dioxide crystals. The silicon dioxide in stone is already as oxidized as it is going to get, and therefore, the spark is mostly light, and very little heat is produced.
The dominant cutting-rock types used in the earliest tools are of the following two classes:
The microcrystalline (cryptocrystalline) forms of SiO2 are flint and chert, which are structurally very different from megacrystalline quartz, and I bet they behave differently when struck together to make sparks.
The other variety of silicon-oxygen containing rocks in paleolithic cultures is obsidian, which isn't even crystalline at all---it's a glass. It would have spark qualities different from flint/chert and quartz. But again, the spark temperature and spark duration may not be enough to ignite surrounding tinder. I would be interested to hear of any research that has been done on the comparative fire-starting properties of flint vs. obsidian, compared to the traditional and tried and true wood-on-wood friction method.
The dominant aboriginal method of producing combustion on all continents is the familiar rotational-friction method of wood-on-wood. This method obviously produces fire by plan, not by accident, and it is doubtful that the friction method was an early hominid development around 3 m.y.a
I can't imagine how the earliest hominids created fire; maybe they saved fire that had already been started by nature, and kept it going for their own use. (maybe one member of the hominid group was selected as the official "fire-tender", who did nothing but keep the communal fire going).
Phillip Bigelow
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