Carbon 14 radioactive dating used
When much later, an archaeologist examines the remains (fireplace ashes, bones, plant remains), he can date the fossil by comparing the fraction of remaining radiocarbon nuclei to the fraction existing at the time the organism stopped absorbing carbon.
The fundamental hypothesis in these estimations is that the rate of radioactive carbon existing when the organism was living would have been the same as the rate in a similar organism alive today.
One naturally assumes that the cosmic bombardment responsible for this transmutation remains constant over the millennia.
The rate of cosmic rays which hit the Earth depends on two very slowly changing factors: the solar activity and the Earth's magnetic field.
This latter serves as a shield against all cosmic radiation - when its strength goes down, the bombardment increases, as does the number of carbon 14 atoms.
The estimation assumes that the rate of formation of atmospheric carbon 14 has not changed since the days when the fossil was alive.After death the amount of carbon-14 in the organic specimen decreases very regularly as the molecules decay.Carbon-14 has a half-life of 5,730 ± 40 years, meaning that every 5,700 years or so the object loses half its carbon-14.It has been replaced since 2004 by Artemis, a mass spectrometer capable of dating each year 4,500 samples of less than a milligram. Love-hungry teenagers and archaeologists agree: dating is hard.