Limitations of radiocarbon dating
You have to know what the atmospheric carbon level (the radiocarbon 'reservoir') was like at the time of an organism's death, in order to be able to calculate how much time has passed since the organism died.
The half-life of an isotope like C14 is the time it takes for half of it to decay away: in C14, every 5,730 years, half of it is gone.It uses the fact that natural carbon contains a known ratio of ordinary carbon and the radioactive isotope carbon-14, and that this mix is reflected in carbon taken up by living organic materials such as wood, shells and bones.When organisms die, the carbon-14 begins to decay at a known rate.Shy of a date stamp on an object, it is still the best and most accurate of dating techniques devised.All living things exchange the gas Carbon 14 (C14) with the atmosphere around them—animals and plants exchange Carbon 14 with the atmosphere, fish and corals exchange carbon with dissolved C14 in the water.A number of methods are used, all of which have their advantages, limitations and level of accuracy.
Complex dating problems often use a variety of techniques and information to arrive at the best answer.
Four main methods have been used in Willandra archaeology.
This well known method was the first technique that became available for accurate dating of old materials.
So, if you measure the amount of C14 in a dead organism, you can figure out how long ago it stopped exchanging carbon with its atmosphere.
Given relatively pristine circumstances, a radiocarbon lab can measure the amount of radiocarbon accurately in a dead organism for as long as 50,000 years ago; after that, there's not enough C14 left to measure. Carbon in the atmosphere fluctuates with the strength of earth's magnetic field and solar activity.
Dates above and below a location provide minimum and maximum age determinations according to the law of superimposition.