Potassium argon radioactive dating works because

“A round [stone] covered the opening of one of the shells, and underneath it was absolutely bright red,” said study leader Christopher Henshilwood, an archaeologist at the University of Bergen in Norway and the University of the Witwatersrand in South Africa.In addition to the shells, the team also found grindstones, hammerstones, the remains of a small fire pit, and animal bones that were used to transfer small amounts of the paint.They do this at a constant rate called an isotope’s “half-life”.Most carbon comes in the stable forms of carbon-12 (six protons, six neutrons) or carbon-13, but a very small amount (about 0.0000000001%) exists as the radioactive carbon-14 (six protons, eight neutrons).“The mixture was very gently stirred, and you can see the traces of the stirring [done by fingers] on the bottom surface of the abalone shell,” Henshilwood said.It’s not clear what the ochre paint was later used for, but Henshilwood said it’s easy to imagine early humans using the substance to decorate their bodies or cave walls.Previously, the earliest evidence of abstract art came mainly in France from the Eurasian Palaeolithic period less than 35,000 years ago.

The abstract art was found on two pieces of ochre in a cave on the southern Cape shore of the Indian Ocean.There is a system to the patterns.””We don’t know what they mean, but they are symbols that I think could have been interpreted by those people as having meaning that would have been understood by others.”The engraved ochre pieces were recovered from Middle Stone Age layers at Blombos Cave, 290 kilometres (180 miles) east of Cape Town, and are at least 70,000 years old.Dr Henshilwood says more than 8,000 other pieces of ochre were found in the cave, many of which had been rubbed smooth as if to make pigment powder.Ochre, a form of iron ore, is frequently found in Stone Age deposits less than 100,000 years old.It may have been used as a body or decorative paint.These different forms of an element—called isotopes—are inherently stable or unstable.The latter are called radioactive isotopes, and over time they will decay, giving off particles (neutrons or protons) and energy (radiation) and therefore turn into another isotope or element.Blombos Cave has been inhabited off and on by humans for at least 140,000 years, but the ochre-paint studio seems to have been active about 100,000 years ago.Prior to the new discovery, the earliest known ochre-making workshop was 60,000 years old, Henshilwood said.The powder was found inside two shells in Blombos Cave near Still Bay, South Africa.The substance is the dried remains of a primitive form of paint made by combining colorful clay called ochre, crushed seal bones, charcoal, quartzite chips, and a liquid, such as water.

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