In a stratigraphical context objects closer to the surface are more recent in time relative to items deeper in the ground.
Although relative dating can work well in certain areas, several problems arise.
Radiocarbon is then taken in by plants through photosynthesis, and these plants in turn are consumed by all the organisms on the planet.
So every living thing has a certain amount of radiocarbon within them.
Therefore, radiocarbon dates need to be calibrated with other dating techniques to ensure accuracy.
Plants are not the only organism that can process Carbon-14 from the air.
Rodents, for example, can create havoc in a site by moving items from one context to another.
Natural disasters like floods can sweep away top layers of sites to other locations.
An extensive tree-ring sequence from the present to 6700 BC was developed in Arizona using California bristlecone pine (), some of which are 4900 years old, making them the oldest living things on earth. In fact, levels of Carbon-14 have varied in the atmosphere through time.One good example would be the elevated levels of Carbon-14 in our atmosphere since WWII as a result of atomic bombs testing.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.Looking at the graph, 100% of radiocarbon in a sample will be reduced to 50% after 5730 years.