All living things absorb both types of carbon; but once it dies, it will stop absorbing.The C-12 is a very stable element and will not change form after being absorbed; however, C-14 is highly unstable and in fact will immediately begin changing after absorption.Specifically, there are two types of carbon found in organic materials: carbon 12 (C-12) and carbon 14 (C-14).It is imperative to remember that the material must have been alive at one point to absorb the carbon, meaning that carbon dating of rocks or other inorganic objects is nothing more than inaccurate guesswork.
This rate of decay, thankfully, is constant, and can be easily measured in terms of ‘half-life’.
Since the universe is estimated to be millions of years old, it was assumed that this equilibrium had already been reached.
However, in the 1960s, the growth rate was found to be significantly higher than the decay rate; almost a third in fact.
By looking at other outcrops in the area, our geologist is able to draw a geological map which records how the rocks are related to each other in the field.
From the mapped field relationships, it is a simple matter to work out a geological cross-section and the relative timing of the geologic events.