Radio Carbon Dating
Radio Carbon Dating is one arguably the most exciting method of dating objects which are less than 50,000 years old.
How does it work ?
When cosmic rays strike Nitrogen 14 in the upper atmosphere, radio-active Carbon 14 results, which is absorbed by plants. Any animal that eats the plant will absorb the Carbon 14 into their bodies. When that animal dies, it stops eating plants, and the amount of Carbon 14 in that animal starts to reduce as it reverts back to Nitrogen 14. It takes 5730 years for an amount of decaying Carbon 14 to halve ( termed the "half-life" ), so we can measure the amount left in the animal and work out how much time would have elapsed since the animals death. Obviously as the animal gets older, the amount left in the body gets smaller and smaller, and it becomes more difficult to date it accurately - for this reason we can't accurately date objects older than about 35,000 years old.
Radio Carbon dating is based on a couple of key assumptions. One of these is that the amount of Carbon 14 produced is constant. In fact, this is not the case as the amount of cosmic rays bombarding our atmosphere is related to the strength of the earth's magnetic field which changes over time. Secondly, nuclear testing has released more Carbon 14 into the atmosphere. Nevertheless, it is still the major method of testing, and the accuracy is improved by using other dating techniques such as Dendrochronology (tree-ring dating), Varve-dating (looking at silt deposits in rivers which are laid down every year) and ice-dating (looking at layers in ice-flows).
Pictographs can be dated by looking for organic materials in the "paints", such as blood, pollen etc.
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