Plankton absorbs, Carbon-14 from the ocean much like terrestrial plants absorb Carbon-14 from the air.Since plankton is the foundation of the marine food chain, Carbon-14 is spread throughout aquatic life.Radiocarbon is then taken in by plants through photosynthesis, and these plants in turn are consumed by all the organisms on the planet.
After an organism dies, the radiocarbon decreases through a regular pattern of decay. The time taken for half of the atoms of a radioactive isotope to decay in Carbon-14’s case is about 5730 years.
Half-lives vary according to the isotope, for example, Uranium-238 has a half-life of 4500 million years where as Nitrogen-17 has a half-life of 4.173 seconds!
There are two techniques for dating in archaeological sites: relative and absolute dating.
Relative dating stems from the idea that something is younger or older relative to something else.
In a stratigraphical context objects closer to the surface are more recent in time relative to items deeper in the ground.