Isotopes of carbon in the context of "Radionuclide"

Before Present (BP) or "years before present (YBP)" is a time scale used mainly in archaeology, geology, and other scientific disciplines to specify when events occurred relative to the origin of practical radiocarbon dating in the 1950s. Because the "present" time changes, standard practice is to use 1 January 1950 as the commencement date (epoch) of the age scale, with 1950 being labelled as the "standard year". The abbreviation "BP" has been interpreted retrospectively as "Before Physics", which refers to the time before nuclear weapons testing artificially altered the proportion of the carbon isotopes in the atmosphere, which scientists must account for when using radiocarbon dating for dates of origin that may fall after this year.

In a convention that is not always observed, many sources restrict the use of BP dates to those produced with radiocarbon dating; the alternative notation "RCYBP" stands for the explicit "radio carbon years before present".

Carbon (from Latin carbo 'coal') is a chemical element; it has symbol C and atomic number 6. It is nonmetallic and tetravalent—meaning that its atoms are able to form up to four covalent bonds due to its valence shell exhibiting 4 electrons. It belongs to group 14 of the periodic table. Carbon makes up about 0.025 percent of Earth's crust. Three isotopes occur naturally, C and C being stable, while C is a radionuclide, decaying with a half-life of 5,700 years. Carbon is one of the few elements known since antiquity.

Carbon is the 15th most abundant element in the Earth's crust, and the fourth most abundant element in the universe by mass after hydrogen, helium, and oxygen. Carbon's abundance, its unique diversity of organic compounds, and its unusual ability to form polymers at the temperatures commonly encountered on Earth, enables this element to serve as a common element of all known life. It is the second most abundant element in the human body by mass (about 18.5%) after oxygen.

Radiocarbon dating (also referred to as carbon dating or carbon-14 dating) is a method for determining the age of an object containing organic material by using the properties of radiocarbon, a radioactive isotope of carbon.

The method was developed in the late 1940s at the University of Chicago by Willard Libby. It is based on the fact that radiocarbon (
C) is constantly being created in the Earth's atmosphere by the interaction of cosmic rays with atmospheric nitrogen. The resulting
C combines with atmospheric oxygen to form radioactive carbon dioxide, which is incorporated into plants by photosynthesis; animals then acquire
C by eating the plants. When the animal or plant dies, it stops exchanging carbon with its environment, and thereafter the amount of
C it contains begins to decrease as the
C undergoes radioactive decay. Measuring the amount of
C 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. The older a sample is, the less
C there is to be detected. The half-life of
C (the period of time after which half of a given sample will have decayed) is about 5,730 years, so the oldest dates that can be reliably measured by this process date to approximately 50,000 years ago, although special preparation methods occasionally make an accurate analysis of older samples possible. Libby received the Nobel Prize in Chemistry for his work in 1960.

The Dresser Formation is a Paleoarchean geologic formation that outcrops as a generally circular ring of hills in the North Pole Dome area of the East Pilbara Terrane of the Pilbara Craton of Western Australia. This formation is one of many formations that comprise the Warrawoona Group, which is the lowermost of four groups that comprise the Pilbara Supergroup. The Dresser Formation is part of the Panorama greenstone belt that surrounds and outcrops around the intrusive North Pole Monzogranite. Dresser Formation consists of metamorphosed, blue, black, and white bedded chert; pillow basalt; carbonate rocks; minor felsic volcaniclastic sandstone and conglomerate; hydrothermal barite; evaporites; and stromatolites. The lowermost of three stratigraphic units that comprise the Dresser Formation contains some of the Earth's earliest commonly accepted evidence of life such as morphologically diverse stromatolites, microbially induced sedimentary structures, putative organic microfossils, and biologically fractionated carbon and sulfur isotopic data.

Carbon-12 (C) is the most abundant of the two stable isotopes of carbon (carbon-13 being the other), amounting to 98.93% of element carbon on Earth; its abundance is due to the triple-alpha process by which it is created in stars. Carbon-12 is of particular importance in its use as the standard from which atomic masses of all nuclides are measured, thus, its atomic mass is exactly 12 daltons by definition. Carbon-12 is composed of 6 protons, 6 neutrons, and 6 electrons.

See carbon-13 for means of separating the two isotopes, thereby enriching both.