Radio active dating
Scientists find the ratio of parent isotope to daughter isotope.
By comparing this ratio to the half-life logarithmic scale of the parent isotope, they are able to find the age of the rock or fossil in question.
The parent isotope is the original unstable isotope, and daughter isotopes are the stable product of the decay. In the first 5,730 years, the organism will lose half of its C-14 isotopes.
Half-life is the amount of time it takes for half of the parent isotopes to decay. In another 5,730 years, the organism will lose another half of the remaining C-14 isotopes.
CEA Radioactive hourglasses are used to date the relics of bygone civilizations, by measuring the amount of Carbon-14, whose decay rate allows for precise age calculations.
The older the sample, the more carbon 14 will have decayed and the emptier the hourglass will be.
Some corrections are necessary, since the amount of carbon 14 present in the atmosphere has varied over the last 40,000 years.
Other dating methods (using the uranium-thorium ratio, for example) reveal the amount by which the carbon 14 results need to be corrected.
For instance, the correction is an approximate 3,000 years increase, for ages of the order of 20,000 years,.