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Carbon Carbon (from la, carbo "coal") is a chemical element Image:Simple Periodic Table Chart-blocks.svg, 400px, Periodic table, The periodic table of the chemical elements In chemistry, an element is a pure substance consisting only of atoms ...
(6C) has 15 known
isotope Isotopes are variants of a particular chemical element which differ in neutron number, and consequently in nucleon number. All isotopes of a given element have the same number of protons but different numbers of neutrons in each atom. The term ...
s, from to , of which and are
stable A stable is a building in which livestock Livestock is commonly defined as domesticated Domestication is a sustained multi-generational relationship in which one group of organisms assumes a significant degree of influence over the reprod ...
. The longest-lived
radioisotope A radionuclide (radioactive nuclide, radioisotope or radioactive isotope) is an atom that has excess nuclear energy, making it unstable. This excess energy can be used in one of three ways: emitted from the nucleus as gamma radiation; transferred ...
is , with a
half-life Half-life (symbol ''t''1⁄2) is the time required for a quantity to reduce to half of its initial value. The term is commonly used in nuclear physics to describe how quickly unstable atoms undergo radioactive decay Radioactive decay (al ...
of years. This is also the only carbon radioisotope found in nature—trace quantities are formed
cosmogenic Cosmogenic nuclides (or cosmogenic isotopes) are rare nuclide A nuclide (or nucleide, from nucleus, also known as nuclear species) is a class of atoms characterized by their number of proton A proton is a subatomic particle, symbol or , with a ...
ally by the reaction + → + . The most stable artificial radioisotope is , which has a half-life of . All other radioisotopes have half-lives under 20 seconds, most less than 200 milliseconds. The least stable isotope is , with a half-life of .


List of isotopes

, - , , style="text-align:right" , 6 , style="text-align:right" , 2 , ,
[] , proton emission, 2p , Subsequently decays by double proton emission to for a net reaction of → + 4 , 0+ , , , - , rowspan=2, , rowspan=2 style="text-align:right" , 6 , rowspan=2 style="text-align:right" , 3 , rowspan=2, , rowspan=2, , β+, p (61.6%) , Immediately decays into two atoms for a net reaction of → 2  + + , rowspan=2, 3/2− , rowspan=2, , rowspan=2, , - , β+,
α
α
(38.4%) , Immediately decays by proton emission to for a net reaction of → 2  + + , - , , style="text-align:right" , 6 , style="text-align:right" , 4 , , , β+ , , 0+ , , , - , rowspan=2, Used for labeling molecules in
PET scans Positron emission tomography (PET) is a functional imaging Functional imaging (or physiological imaging), is a medical imaging technique of detecting or measuring changes in metabolism, blood flow, regional chemical composition, and absorption ...
, rowspan=2 style="text-align:right" , 6 , rowspan=2 style="text-align:right" , 5 , rowspan=2 , , rowspan=2 , , β+ (99.79%) , , rowspan=2 , 3/2− , rowspan=2 , , rowspan=2 , , - ,
EC
EC
(0.21%) , , - , style="text-indent:1em" , , colspan=3 style="text-indent:2em" , , , p , , 1/2+ , , , - , , style="text-align:right" , 6 , style="text-align:right" , 6 , 12 exactlyThe
unified atomic mass unit The dalton or unified atomic mass unit (symbols: Da or u) is a unit Unit may refer to: Arts and entertainment * UNIT, a fictional military organization in the science fiction television series ''Doctor Who'' * Unit of action, a discrete piece of ...
is defined as 1/12 the mass of an unbound atom of carbon-12 at ground state
, colspan=3 align=center, Stable , 0+ , ref name="Atomic Weight of Carbon">
, - , Ratio of 12C to 13C used to measure biological productivity in ancient times and differing types of
photosynthesis File:Photosynthesis equation.svg, upright=1.8, Overall equation for the type of photosynthesis that occurs in plants Photosynthesis is a process used by plants and other organisms to Energy transformation, convert light energy into chemical energ ...

photosynthesis
, style="text-align:right" , 6 , style="text-align:right" , 7 , , colspan=3 align=center, Stable , 1/2− , ref name="Atomic Weight of Hydrogen">
, - , Has an important use in
radiodating Radiometric dating, radioactive dating or radioisotope dating is a technique which is used to date materials such as rocks A rock is any naturally occurring solid mass or aggregate of minerals or mineraloid matter. It is categorized by the ...
(see
carbon dating Radiocarbon dating (also referred to as carbon dating or carbon-14 dating) is a method for Chronological dating, determining the age of an object containing organic material by using the properties of carbon-14, radiocarbon, a radioactive Isotopes ...
)
, style="text-align:right" , 6 , style="text-align:right" , 8 , , , β , , 0+ , TracePrimarily
cosmogenic Cosmogenic nuclides (or cosmogenic isotopes) are rare nuclide A nuclide (or nucleide, from nucleus, also known as nuclear species) is a class of atoms characterized by their number of proton A proton is a subatomic particle, symbol or , with a ...
, produced by
neutron The neutron is a subatomic particle, symbol or , which has a neutral (not positive or negative) charge, and a mass slightly greater than that of a proton. Protons and neutrons constitute the nuclei of atoms. Since protons and neutrons behav ...

neutron
s striking atoms of ( + → + )
, <10−12 , - , style="text-indent:1em" , , colspan="3" style="text-indent:2em" , , , IT , , (2−) , , , - , , style="text-align:right" , 6 , style="text-align:right" , 9 , , , β , , 1/2+ , , , - , rowspan=2, , rowspan=2 style="text-align:right" , 6 , rowspan=2 style="text-align:right" , 10 , rowspan=2, , rowspan=2, , β, n (99.0%) , , rowspan=2, 0+ , rowspan=2, , rowspan=2, , - , β (1.0%) , , - , rowspan=2, , rowspan=2 style="text-align:right" , 6 , rowspan=2 style="text-align:right" , 11 , rowspan=2, , rowspan=2, , β (71.6%) , , rowspan=2, 3/2+ , rowspan=2, , rowspan=2, , - , β, n (28.4%) , , - , rowspan=2, , rowspan=2 style="text-align:right" , 6 , rowspan=2 style="text-align:right" , 12 , rowspan=2, , rowspan=2, , β (68.5%) , , rowspan=2, 0+ , rowspan=2, , rowspan=2, , - , β, n (31.5%) , , - , rowspan=3, Has 1
halo Halo generally refers to: * Halo (optical phenomenon) * Halo (religious iconography), a glow or ring of light around a head or person in art or a ring above one's head * Halo (franchise), ''Halo'' (franchise), a video game franchise Halo or HALO ...
neutron
, rowspan=3 style="text-align:right" , 6 , rowspan=3 style="text-align:right" , 13 , rowspan=3, , rowspan=3, , β, n (47%) , , rowspan=3, 1/2+ , rowspan=3, , rowspan=3, , - , β (46%) , , - , β, 2n (7%) , , - , rowspan=3, , rowspan=3 style="text-align:right" , 6 , rowspan=3 style="text-align:right" , 14 , rowspan=3, , rowspan=3, , β, n (70%) , , rowspan=3, 0+ , rowspan=3, , rowspan=3, , - , β, 2n (<18.6%) , , - , β (>11.4%) , , - , , style="text-align:right" , 6 , style="text-align:right" , 15 , # , < , n , , 1/2+# , , , - , rowspan=3, Has 2 halo neutrons , rowspan=3 style="text-align:right" , 6 , rowspan=3 style="text-align:right" , 16 , rowspan=3, , rowspan=3, , β, n (61%) , , rowspan=3, 0+ , rowspan=3, , rowspan=3, , - , β, 2n (<37%) , , - , β (>2%) ,


Carbon-11

Carbon-11 or is a radioactive isotope of
carbon Carbon (from la, carbo "coal") is a chemical element with the Symbol (chemistry), symbol C and atomic number 6. It is nonmetallic and tetravalence, tetravalent—making four electrons available to form covalent bond, covalent chemical bonds. ...

carbon
that decays to
boron-11 Boron is a chemical element Image:Simple Periodic Table Chart-blocks.svg, 400px, Periodic table, The periodic table of the chemical elements In chemistry, an element is a pure substance consisting only of atoms that all have the same num ...

boron-11
. This decay mainly occurs due to
positron emission Positron emission or beta plus decay (β+ decay) is a subtype of radioactive decay Radioactive decay (also known as nuclear decay, radioactivity, radioactive disintegration or nuclear disintegration) is the process by which an unstable atomic ...
, with around 0.19–0.23% of decays instead occurring by
electron capture Electron capture (K-electron capture, also K-capture, or L-electron capture, L-capture) is a process in which the proton-rich nucleus of an electrically neutral atom absorbs an inner atomic electron, usually from the K or L electron shells. Th ...

electron capture
. It has a
half-life Half-life (symbol ''t''1⁄2) is the time required for a quantity to reduce to half of its initial value. The term is commonly used in nuclear physics to describe how quickly unstable atoms undergo radioactive decay Radioactive decay (al ...
of 20.364 minutes. : : It is produced from nitrogen in a
cyclotron . The magnet is painted yellow. A cyclotron is a type of particle accelerator , a synchrotron collider type particle accelerator at Fermi National Accelerator Laboratory (Fermilab), Batavia, Illinois, USA. Shut down in 2011, until 2007 it wa ...

cyclotron
by the reaction : + → + Carbon-11 is commonly used as a
radioisotope A radionuclide (radioactive nuclide, radioisotope or radioactive isotope) is a nuclide A nuclide (or nucleide, from nucleus, also known as nuclear species) is a class of atoms characterized by their number of proton A proton is a subatomic par ...
for the radioactive labeling of molecules in
positron emission tomography Positron emission tomography (PET) is a functional imaging Functional imaging (or physiological imaging), is a medical imaging technique of detecting or measuring changes in metabolism, blood flow, regional chemical composition, and absorptio ...
. Among the many molecules used in this context are the
radioligand A radioligand is a radioactive biochemical substance (in particular, a ligand (biochemistry), ligand that is radioactive tracer, radiolabeled) that is used for diagnosis or for research-oriented study of the receptor (biochemistry), receptor systems ...
s


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Natural isotopes

There are three naturally occurring isotopes of carbon: 12, 13, and 14. and are stable, occurring in Δ13C, a natural proportion of approximately 93:1. is produced by thermal neutrons from cosmic radiation in the upper atmosphere, and is transported down to earth to be absorbed by living biological material. Isotopically, constitutes a negligible part; but, since it is radioactive with a half-life of years, it is radiometrically detectable. Since dead tissue does not absorb , the amount of is one of the methods used within the field of archeology for
radiometric dating Radiometric dating, radioactive dating or radioisotope dating is a technique which is used to date materials such as rocks A rock is any naturally occurring solid mass or aggregate of minerals or mineraloid matter. It is categorized by the ...
of biological material.


Paleoclimate

and are measured as the
isotope ratio The term stable isotope has a meaning similar to stable nuclide, but is preferably used when speaking of nuclides of a specific element. Hence, the plural form stable isotopes usually refers to isotope Isotopes are variants of a particular c ...
δ13C in
benthic The benthic zone is the ecological region at the lowest level of a body of water ( Lysefjord) in Norway Norway ( nb, ; nn, ; se, Norga; smj, Vuodna; sma, Nöörje), officially the Kingdom of Norway, is a Nordic countries, Nordic ...
foraminifera Foraminifera (; Latin for "hole bearers"; informally called "forams") are single-celled organisms, members of a phylum or class (biology), class of Amoeba, amoeboid protists characterized by streaming granular Ectoplasm (cell biology), ectoplasm ...
and used as a
proxy Proxy may refer to: * Proxy or agent (law), a substitute authorized to act for another entity or a document which authorizes the agent so to act * Proxy (climate), a measured variable used to infer the value of a variable of interest in climate r ...
for
nutrient cycling A nutrient cycle (or ecological recycling) is the movement and exchange of organic matter, organic and inorganic matter back into the Productivity (ecology), production of matter. Energy flow is a unidirectional and noncyclic pathway, whereas the ...
and the temperature dependent air-sea exchange of CO2 (ventilation) ( Lynch-Stieglitz et al., 1995). Plants find it easier to use the lighter isotopes () when they convert sunlight and carbon dioxide into food. So, for example, large blooms of
plankton Plankton are the diverse collection of organism In biology, an organism () is any organic, life, living system that functions as an individual entity. All organisms are composed of cells (cell theory). Organisms are classified by tax ...

plankton
(free-floating organisms) absorb large amounts of from the oceans. Originally, the was mostly incorporated into the seawater from the atmosphere. If the oceans that the plankton live in are stratified (meaning that there are layers of warm water near the top, and colder water deeper down), then the surface water does not mix very much with the deeper waters, so that when the plankton dies, it sinks and takes away from the surface, leaving the surface layers relatively rich in . Where cold waters well up from the depths (such as in the North Atlantic), the water carries back up with it. So, when the ocean was less stratified than today, there was much more in the skeletons of surface-dwelling species. Other indicators of past climate include the presence of tropical species, coral growths rings, etc.
Tim Flannery Timothy Fridtjof Flannery (born 28 January 1956) is an Australian mammalogist In zoology Zoology ()The pronunciation of zoology as is typically regarded as nonstandard, though it is not uncommon. is the branch of biology that studies the an ...

Tim Flannery
''The weather makers: the history & future of climate change'', The Text Publishing Company, Melbourne, Australia.


Tracing food sources and diets

The quantities of the different isotopes can be measured by
mass spectrometry Mass spectrometry (MS) is an analytical technique that is used to measure the mass-to-charge ratio of ions. The results are presented as a ''mass spectrum'', a plot of intensity as a function of the mass-to-charge ratio. Mass spectrometry is used i ...
and compared to a
standard Standard may refer to: Flags * Colours, standards and guidons * Standard (flag), a type of flag used for personal identification Norm, convention or requirement * Standard (metrology), an object that bears a defined relationship to a unit of ...
; the result (e.g. the delta of the = δ) is expressed as parts per thousand (‰): :\delta \ce = \left( \frac - 1 \right) \times 1000 Stable carbon isotopes in
carbon dioxide Carbon dioxide (chemical formula ) is a colorless gas with a density about 53% higher than that of dry air. Carbon dioxide molecules consist of a carbon atom covalent bond, covalently double bonded to two oxygen atoms. It occurs naturally in At ...

carbon dioxide
are utilized differentially by plants during
photosynthesis File:Photosynthesis equation.svg, upright=1.8, Overall equation for the type of photosynthesis that occurs in plants Photosynthesis is a process used by plants and other organisms to Energy transformation, convert light energy into chemical energ ...

photosynthesis
. Grasses in
temperate climate In geography Geography (from Greek: , ''geographia'', literally "earth description") is a field of science devoted to the study of the lands, features, inhabitants, and phenomena of the Earth and planets. The first person to use ...
s (
barley Barley (''Hordeum vulgare''), a member of the grass family Poaceae () or Gramineae () is a large and nearly ubiquitous family In human society, family (from la, familia) is a group of people related either by consanguinity (by recogn ...

barley
,
rice Rice is the seed of the Poaceae, grass species ''Oryza sativa'' (Asian rice) or less commonly ''Oryza glaberrima'' (African rice). The name wild rice is usually used for species of the genera ''Zizania (genus), Zizania'' and ''Porteresia'', bot ...

rice
,
wheat Wheat is a grass widely cultivated for its seed, a cereal grain which is a worldwide staple food. The many species of wheat together make up the genus ''Triticum''; the most widely grown is common wheat Common wheat (''Triticum aestivum'') ...

wheat
,
rye Rye (''Secale cereale'') is a grass grown extensively as a grain, a cover crop and a forage Forage is a plant material (mainly plant leaves and stems) eaten by grazing livestock. Historically, the term ''forage'' has meant only plants eate ...

rye
and
oats The oat (''Avena sativa''), sometimes called the common oat, is a species In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes ...

oats
, plus
sunflower ''Helianthus'' () is a genus Genus /ˈdʒiː.nəs/ (plural genera /ˈdʒen.ər.ə/) is a taxonomic rank used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, vi ...

sunflower
,
potato The potato is a starch#Food, starchy tuber of the plant ''Solanum tuberosum'' and is a root vegetable native to the Americas. The plant is a perennial plant, perennial in the nightshade family Solanaceae. Wild potato species can be found throu ...

potato
,
tomato The tomato is the edible berry A berry is a small, pulpy, and often edible fruit In botany, a fruit is the seed-bearing structure in flowering plants (also known as angiosperms) formed from the ovary after flowering. Fruits are ...

tomato
es,
peanut The peanut, also known as the groundnut, goober (US), pindar (US) or monkey nut (UK), and taxonomically classified as ''Arachis hypogaea'', is a legume A legume () is a plant Plants are mainly multicellular organisms, predominantly ...

peanut
s,
cotton Cotton is a soft, fluffy staple fiber that grows in a boll, or protective case, around the seeds of the cotton plants of the genus '' Gossypium'' in the mallow family Malvaceae. The fiber is almost pure cellulose. Under natural condition ...

cotton
,
sugar beet A sugar beet is a plant whose root contains a high concentration of sucrose Sucrose is common sugar. It is a disaccharide, a molecule composed of two monosaccharides: glucose and fructose. Sucrose is produced naturally in plants, from which ta ...
, and most trees and their nuts/fruits,
rose A rose is a woody perennial plant, perennial flowering plant of the genus ''Rosa'', in the family Rosaceae, or the flower it bears. There are over three hundred Rose species, species and Garden roses, tens of thousands of cultivars. They form a ...

rose
s and
Kentucky bluegrass ''Poa pratensis'', commonly known as Kentucky bluegrass (or blue grass), smooth meadow-grass, or common meadow-grass, is a perennial A perennial plant or simply perennial is a plant that lives more than two years. The term ('' per-'' + '' ...
) follow a C3 photosynthetic pathway that will yield δ13C values averaging about −26.5‰. Grasses in hot
arid climate The desert climate or arid climate (in the Köppen climate classification ''BWh'' and ''BWk''), is a climate which there is an excess of evaporation over precipitation. The typically bald, rocky, or sandy surfaces in desert climates hold little ...
s (
maize Maize ( ; ''Zea mays'' subsp. ''mays'', from es, maíz after tnq, mahiz), also known as corn ( North American and Australian English), is a cereal grain first domesticated by indigenous peoples Indigenous peoples, also referred to as F ...

maize
in particular, but also
millet Millets () are a group of highly variable small-seeded grasses, widely grown around the world as cereal crops or grains for fodder and human food. Millets are important crops in the semiarid tropics of Asia and Africa (especially in Indi ...

millet
,
sorghum ''Sorghum'' is a genus of about 25 species of flowering plants in the grass family ( Poaceae). Some of these species are grown as cereals for human consumption and some in pastures for animals. One species, '' Sorghum bicolor'', was originally ...

sorghum
,
sugar cane Sugarcane or sugar cane is a species of (often hybrid) tall, Perennial plant, perennial grass (in the genus ''Saccharum'', tribe Andropogoneae) that is used for sugar Sugar industry, production. The plants are 2–6 m (6–20 ft) tall w ...

sugar cane
and crabgrass) follow a C4 photosynthetic pathway that produces δ13C values averaging about −12.5‰.https://www.ldeo.columbia.edu/~polissar/OrgGeochem/oleary-1988-carbon-isotopes.pdf It follows that eating these different plants will affect the δ13C values in the consumer's body tissues. If an animal (or human) eats only C3 plants, their δ13C values will be from −18.5 to −22.0‰ in their bone
collagen upright=1.5, Tropocollagen molecule: three left-handed procollagens (red, green, blue) join to form a right-handed triple helical tropocollagen. Collagen () is the main structural protein Proteins are large biomolecules and macromolecules th ...

collagen
and −14.5‰ in the
hydroxylapatite Hydroxyapatite, also called hydroxylapatite (HA), is a naturally occurring mineral In geology and mineralogy, a mineral or mineral species is, broadly speaking, a solid chemical compound with a fairly well-defined chemical composition and a ...
of their teeth and bones. In contrast, C4 feeders will have bone collagen with a value of −7.5‰ and hydroxylapatite value of −0.5‰. In actual case studies, millet and maize eaters can easily be distinguished from rice and wheat eaters. Studying how these dietary preferences are distributed geographically through time can illuminate migration paths of people and dispersal paths of different agricultural crops. However, human groups have often mixed C3 and C4 plants (northern Chinese historically subsisted on wheat and millet), or mixed plant and animal groups together (for example, southeastern Chinese subsisting on rice and fish).


See also

*
Radiocarbon dating 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 Organic matter, organic material, or natural organic matter refers to the large source of ...
*
Cosmogenic isotope Cosmogenic nuclides (or cosmogenic isotopes) are rare nuclides (isotopes) created when a high-energy cosmic ray interacts with the atomic nucleus, nucleus of an ''in situ'' Solar System atom, causing nucleons (protons and neutrons) to be expelled f ...
s *
Environmental isotopesThe environmental isotopes are a subset of the isotope Isotopes are variants of a particular chemical element which differ in neutron number, and consequently in nucleon number. All isotopes of a given element have the same number of protons but ...
*
Isotopic signatureAn isotopic signature (also isotopic fingerprint) is a ratio of non-radiogenic 'stable isotopes The term stable isotope has a meaning similar to stable nuclide, but is preferably used when speaking of nuclides of a specific element. Hence, the plu ...


References

{{Authority control Carbon
Carbon Carbon (from la, carbo "coal") is a chemical element with the Symbol (chemistry), symbol C and atomic number 6. It is nonmetallic and tetravalence, tetravalent—making four electrons available to form covalent bond, covalent chemical bonds. ...