Over time there is a gradual decrease in the amount of Carbon-14 and the ratio of Carbon-14 atoms to other Carbon atoms declines. Therefore half of the Carbon-14 has decayed after 5730 years.
Half of the remaining Carbon-14 then decays over the next 5730 years leaving one fourth of the original amount.
Measurement of radiocarbon was originally done by beta-counting devices, which counted the amount of beta radiation emitted by decaying atoms in the sample and not just the few that happen to decay during the measurements; it can therefore be used with much smaller samples (as small as individual plant seeds), and gives results much more quickly.
The development of radiocarbon dating has had a profound impact on archaeology.
The resulting data, in the form of a calibration curve, is now used to convert a given measurement of radiocarbon in a sample into an estimate of the sample's calendar age.
Other corrections must be made to account for the proportion of throughout the biosphere (reservoir effects).
Radioactivity is the tendency of an atom to emit ionizing radiation in the form of ionizing particles, sich as alpha or beta particles, or even rays like gamma rays.
Higher radioactive substances are usually unstable isotopes, such as isotopes with a lot of neutrons in them.
Histories of archaeology often refer to its impact as the "radiocarbon revolution".The unstable Carbon-14 is transported down to the lower atmosphere by atmospheric activity such as storms.Carbon-14 reacts identically to Carbon-12 and is rapidly oxidised to form (Carbon-14)Dioxide.The method was developed in the late 1940s by Willard Libby, who received the Nobel Prize in Chemistry for his work in 1960.It is based on the fact that radiocarbon ( in a sample from a dead plant or animal such as a piece of wood or a fragment of bone provides information that can be used to calculate when the animal or plant died.Radiocarbon ages are still calculated using this half-life, and are known as "Conventional Radiocarbon Age".Since the calibration curve (Int Cal) also reports past atmospheric concentration using this conventional age, any conventional ages calibrated against the Int Cal curve will produce a correct calibrated age.For example, two samples taken from the tombs of two Egyptian kings, Zoser and Sneferu, independently dated to 2625 BC plus or minus 75 years, were dated by radiocarbon measurement to an average of 2800 BC plus or minus 250 years. Carbon dioxide produced in this way diffuses in the atmosphere, is dissolved in the ocean, and is taken up by plants via photosynthesis.Animals eat the plants, and ultimately the radiocarbon is distributed throughout the biosphere.The older a sample is, the less (the period of time after which half of a given sample will have decayed) is about 5,730 years, the oldest dates that can be reliably measured by this process date to around 50,000 years ago, although special preparation methods occasionally permit accurate analysis of older samples.Research has been ongoing since the 1960s to determine what the proportion of in the atmosphere has been over the past fifty thousand years.