Carbon-14 Carbon-14 Carbon-14, (C), or radiocarbon, is a radioactive isotope of carbon with an atomic nucleus containing 6 protons and 8 neutrons. Its presence in organic materials is the basis of the radiocarbon dating method pioneered by Willard Libby and colleagues (1949) to date archaeological, geological and hydrogeological samples. Carbon-14 was discovered on February 27, 1940, by Martin Kamen and Sam Ruben at the University of California Radiation Laboratory in Berkeley, California. Its existence had been suggested by Franz Kurie in 1934. There are three naturally occurring isotopes of carbon on Earth: carbon-12, which makes up 99% of all carbon on
Stable-isotope probing organisms were consuming existing carbohydrates and which were using carbohydrates more recently produced from photosynthesis. When DNA is the biomarker, SIP theoretically can be performed using isotopically labeled C, H, O or N, though C is used most often. Cupples et al. (2007) demonstrated a weaker DNA buoyant density shift in when N- versus C-labeled substrates were used in pure culture, conversely a very strong buoyant density shift was observed when both labels were used. Stable-isotope probing Stable-isotope probing (SIP) is a technique in microbial ecology for tracing fluxes of nutrients in biogeochemical cycling by microorganisms. A substrate is enriched