Carbon 14 dating denotes amount

The half-life () is the name given to this value which Libby measured at 556830 years. After 10 half-lives, there is a very small amount of radioactive carbon present in a sample.

At about 50 - 60 000 years, then, the limit of the technique is reached (beyond this time, other radiometric techniques must be used for dating).

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Renfrew (1973) called it 'the radiocarbon revolution' in describing its impact upon the human sciences.

Oakley (1979) suggested its development meant an almost complete re-writing of the evolution and cultural emergence of the human species.

"Everything which has come down to us from heathendom is wrapped in a thick fog; it belongs to a space of time we cannot measure.

We know that it is older than Christendom, but whether by a couple of years or a couple of centuries, or even by more than a millenium, we can do no more than guess." [Rasmus Nyerup, (Danish antiquarian), 1802 (in Trigger, 19)].

They exist in equilibrium with the C14 concentration of the atmosphere, that is, the numbers of C14 atoms and non-radioactive carbon atoms stays approximately the same over time.

As soon as a plant or animal dies, they cease the metabolic function of carbon uptake; there is no replenishment of radioactive carbon, only decay.

The 14C formed is rapidly oxidised to 14CO2 and enters the earth's plant and animal lifeways through photosynthesis and the food chain.

The rapidity of the dispersal of C14 into the atmosphere has been demonstrated by measurements of radioactive carbon produced from thermonuclear bomb testing.

Once an organism is dead, however, no new carbon is actively absorbed by its tissues, and its carbon 14 gradually decays.

Libby thus reasoned that by measuring carbon 14 levels in the remains of an organism that died long ago, one could estimate the time of its death.

A technique for measuring the age of organic remains based on the rate of decay of carbon 14.

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