Radiocarbon, or carbon 14, is an isotope of the element carbon that is unstable and weakly radioactive. Carbon 14 is continually being formed in the upper atmosphere by the effect of cosmic ray neutrons on nitrogen 14 atoms.It is rapidly oxidized in air to form carbon dioxide and enters the global carbon cycle.Radiocarbon dating was invented in the late 1940s, and within a few decades, it was discovered that while the dates retrieved from the method have a sound, repeatable progression, they are not a one-to-one match with calendar years.Most importantly, researchers discovered that radiocarbon dates are affected by the amount of carbon in the atmosphere, which has fluctuated greatly in the past for both natural and human-caused reasons (such as the invention of iron smelting, the Industrial Revolution and the invention of the combustion engine). The problem is, of course, that CE and BCE still use the putative date of the birth of Christ as the reference points for its numbering system: the two years 1 BCE, 1 CE are equivalent to 1 BC, 1 AD.Plants and animals assimilate carbon 14 from carbon dioxide throughout their lifetimes.When they die, they stop exchanging carbon with the biosphere and their carbon 14 content then starts to decrease at a rate determined by the law of radioactive decay. Ninety-five percent of the activity of Oxalic Acid from the year 1950 is equal to the measured activity of the absolute radiocarbon standard which is 1890 wood.
BP was first established as a way to clarify the relationship between calendar years and radiocarbon dates. C., with their explicit references to Christianity, or to use the alternatives C. At the same time, atmospheric nuclear testing, which throws huge amounts of carbon into our atmosphere, was begun in the 1940s.One advantage to using BP is it avoids the occasionally ire-filled philosophical debate about whether, in this multicultural world of ours, it is more appropriate to use A. Radiocarbon dates after 1950 are virtually useless unless and until we can figure out a way to calibrate for the excessive amount of carbon still increasing in our atmosphere.Nonetheless, 1950 is a very long time ago now--should we adjust the starting point to 2050?This is calculated through careful measurement of the residual activity (per gram C) remaining in a sample whose age is Unknown, compared with the activity present in Modern and Background samples. Thus 1950, is year 0 BP by convention in radiocarbon dating and is deemed to be the 'present'.You can get an idea of the relationship between C14 and age at the Carbon Dating calculator page. 1950 was chosen for no particular reason other than to honour the publication of the first radiocarbon dates calculated in December 1949 (Taylor, 19).