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!
Limitations and calibration: When Libby was first determining radiocarbon dates, he found that before 1000 BC his dates were earlier than calendar dates.
He had assumed that amounts of Carbon-14 in the atmosphere had remained constant through time.
As long as there is organic material present, radiocarbon dating is a universal dating technique that can be applied anywhere in the world.
It is good for dating for the last 50,000 years to about 400 years ago and can create chronologies for areas that previously lacked calendars.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.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.Shellfish remains are common in coastal and estuarine archaeological sites, but dating these samples require a correction for the “reservoir effect” a process whereby "old carbon" is recycled and incorporated into marine life especially shellfish inflating their actual age in some cases several centuries.In recognition of this problem archaeologists have developed regional reservoir correction rates based on ocean bottom topography, water temperature, coastline shape and paired samples of terrestrial and marine objects found together in an archaeological feature such as a hearth.When it comes to dating archaeological samples, several timescale problems arise.For example, Christian time counts the birth of Christ as the beginning, AD 1 (Anno Domini); everything that occurred before Christ is counted backwards from AD as BC (Before Christ).The Mayan calendar used 3114 BC as their reference.More recently is the radiocarbon date of 1950 AD or before present, BP.