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.Fossil fuels such as coal and oil are made primarily of plant material that was deposited millions of years ago.
To determine the year age (absolute age) of an object, a number of chemical and radioactive techniques can be used.
Chlorofluorocarbons (CFCs) are fully halogenated paraffin hydrocarbons that contain only carbon, chlorine, and fluorine, produced as volatile derivative of methane, ethane, and propane.
They are also commonly known by the Du Pont brand name Freon.
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.