An isotopic signature (also isotopic fingerprint) is a ratio of non-radiogenic '
stable isotopes', stable
radiogenic isotopes
A radiogenic nuclide is a nuclide that is produced by a process of radioactive decay. It may itself be radioactive (a radionuclide) or stable (a stable nuclide).
Radiogenic nuclides (more commonly referred to as radiogenic isotopes) form some ...
, or unstable
radioactive
Radioactive decay (also known as nuclear decay, radioactivity, radioactive disintegration, or nuclear disintegration) is the process by which an unstable atomic nucleus loses energy by radiation. A material containing unstable nuclei is consi ...
isotopes of particular elements in an investigated material. The ratios of isotopes in a sample material are measured by
isotope-ratio mass spectrometry
Isotope-ratio mass spectrometry (IRMS) is a specialization of mass spectrometry, in which mass spectrometric methods are used to measure the relative abundance of isotopes in a given sample.
This technique has two different applications in the ea ...
against an
isotopic reference material. This process is called
isotope analysis.
Stable isotopes
The
atomic mass
The atomic mass (''m''a or ''m'') is the mass of an atom. Although the SI unit of mass is the kilogram (symbol: kg), atomic mass is often expressed in the non-SI unit dalton (symbol: Da) – equivalently, unified atomic mass unit (u). 1&nb ...
of different isotopes affect their
chemical kinetic behavior, leading to natural
isotope separation
Isotope separation is the process of concentrating specific isotopes of a chemical element by removing other isotopes. The use of the nuclides produced is varied. The largest variety is used in research (e.g. in chemistry where atoms of "marker" n ...
processes.
Carbon isotopes
For example, different sources and sinks of
methane
Methane ( , ) is a chemical compound with the chemical formula (one carbon atom bonded to four hydrogen atoms). It is a group-14 hydride, the simplest alkane, and the main constituent of natural gas. The relative abundance of methane on Ea ...
have different affinity for the
12C and
13C isotopes, which allows distinguishing between different sources by the
13C/
12C ratio in methane in the air. In
geochemistry
Geochemistry is the science that uses the tools and principles of chemistry to explain the mechanisms behind major geological systems such as the Earth's crust and its oceans. The realm of geochemistry extends beyond the Earth, encompassing the ...
,
paleoclimatology
Paleoclimatology (American and British English spelling differences, British spelling, palaeoclimatology) is the study of climates for which direct measurements were not taken. As instrumental records only span a tiny part of Earth's history, the ...
and
paleoceanography
Paleoceanography is the study of the history of the oceans in the geologic past with regard to circulation, chemistry, biology, geology and patterns of sedimentation and biological productivity. Paleoceanographic studies using environment models ...
this ratio is called
δ13C. The ratio is calculated with respect to
Pee Dee Belemnite (PDB)
standard Standard may refer to:
Symbols
* Colours, standards and guidons, kinds of military signs
* Standard (emblem), a type of a large symbol or emblem used for identification
Norms, conventions or requirements
* Standard (metrology), an object th ...
:
:
‰
Similarly, carbon in inorganic
carbonate
A carbonate is a salt of carbonic acid (H2CO3), characterized by the presence of the carbonate ion, a polyatomic ion with the formula . The word ''carbonate'' may also refer to a carbonate ester, an organic compound containing the carbonate ...
s shows little isotopic fractionation, while carbon in materials originated by
photosynthesis
Photosynthesis is a process used by plants and other organisms to convert light energy into chemical energy that, through cellular respiration, can later be released to fuel the organism's activities. Some of this chemical energy is stored i ...
is depleted of the heavier isotopes. In addition, there are two types of plants with different biochemical pathways; the
C3 carbon fixation
carbon fixation is the most common of three metabolic pathways for carbon fixation in photosynthesis, along with C4 carbon fixation, and Crassulacean acid metabolism, CAM. This process converts carbon dioxide and ribulose bisphosphate (RuBP, a ...
, where the isotope separation effect is more pronounced,
C4 carbon fixation, where the heavier
13C is less depleted, and
Crassulacean Acid Metabolism
Crassulacean acid metabolism, also known as CAM photosynthesis, is a carbon fixation pathway that evolved in some plants as an adaptation to arid conditions that allows a plant to photosynthesize during the day, but only exchange gases at night. ...
(CAM) plants, where the effect is similar but less pronounced than with C
4 plants. Isotopic fractionation in plants is caused by physical (slower diffusion of
13C in plant tissues due to increased atomic weight) and biochemical (preference of
12C by two enzymes:
RuBisCO
Ribulose-1,5-bisphosphate carboxylase-oxygenase, commonly known by the abbreviations RuBisCo, rubisco, RuBPCase, or RuBPco, is an enzyme () involved in the first major step of carbon fixation, a process by which atmospheric carbon dioxide is con ...
and
phosphoenolpyruvate carboxylase
Phosphoenolpyruvate carboxylase (also known as PEP carboxylase, PEPCase, or PEPC; , PDB ID: 3ZGE) is an enzyme in the family of carboxy-lyases found in plants and some bacteria that catalyzes the addition of bicarbonate (HCO3−) to phosphoenol ...
) factors. The different isotope ratios for the two kinds of plants propagate through the
food chain
A food chain is a linear network of links in a food web starting from producer organisms (such as grass or algae which produce their own food via photosynthesis) and ending at an apex predator species (like grizzly bears or killer whales), de ...
, thus it is possible to determine if the principal diet of a human or an animal consists primarily of C
3 plants (
rice
Rice is the seed of the 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'' and '' Porteresia'', both wild and domesticat ...
,
wheat
Wheat is a grass widely cultivated for its seed, a cereal grain that is a worldwide staple food. The many species of wheat together make up the genus ''Triticum'' ; the most widely grown is common wheat (''T. aestivum''). The archaeologi ...
,
soybeans,
potato
The potato is a starchy food, a tuber of the plant ''Solanum tuberosum'' and is a root vegetable native to the Americas. The plant is a perennial in the nightshade family Solanaceae.
Wild potato species can be found from the southern Unit ...
es) or C
4 plants (
corn, or
corn-fed beef
There are different systems of feeding cattle in animal husbandry. For pastured animals, grass is usually the forage that composes the majority of their diet. Cattle reared in feedlots are fed hay supplemented with grain, soy and other ingredie ...
) by
isotope analysis of their flesh and bone collagen (however, to obtain more accurate determinations, carbon isotopic fractionation must be also taken into account, since several studies have reported significant
13C discrimination during biodegradation of simple and complex substrates).
Within C3 plants processes regulating changes in δ
13C are well understood, particularly at the leaf level,
but also during wood formation.
Many recent studies combine leaf level isotopic fractionation with annual patterns of wood formation (i.e. tree ring δ
13C) to quantify the impacts of climatic variations and atmospheric composition
on physiological processes of individual trees and forest stands.
The next phase of understanding, in terrestrial ecosystems at least, seems to be the combination of multiple isotopic proxies to decipher interactions between plants, soils and the atmosphere, and predict how changes in land use will affect climate change.
Similarly, marine fish contain more
13C than freshwater fish, with values approximating the C
4 and C
3 plants respectively.
The ratio of carbon-13 and carbon-12 isotopes in these types of plants is as follows:
* C
4 plants: -16 to -10 ‰
* CAM plants: -20 to -10 ‰
* C
3 plants: -33 to -24 ‰
Limestone
Limestone ( calcium carbonate ) is a type of carbonate sedimentary rock which is the main source of the material lime. It is composed mostly of the minerals calcite and aragonite, which are different crystal forms of . Limestone forms whe ...
s formed by precipitation in
sea
The sea, connected as the world ocean or simply the ocean, is the body of salty water that covers approximately 71% of the Earth's surface. The word sea is also used to denote second-order sections of the sea, such as the Mediterranean Sea, ...
s from the atmospheric carbon dioxide contain normal proportion of
13C. Conversely,
calcite found in
salt dome
A salt dome is a type of structural dome formed when salt (or other evaporite minerals) intrudes into overlying rocks in a process known as diapirism. Salt domes can have unique surface and subsurface structures, and they can be discovered usin ...
s originates from carbon dioxide formed by
oxidation
Redox (reduction–oxidation, , ) is a type of chemical reaction in which the oxidation states of substrate change. Oxidation is the loss of electrons or an increase in the oxidation state, while reduction is the gain of electrons or a ...
of
petroleum
Petroleum, also known as crude oil, or simply oil, is a naturally occurring yellowish-black liquid mixture of mainly hydrocarbons, and is found in geological formations. The name ''petroleum'' covers both naturally occurring unprocessed crud ...
, which due to its plant origin is
13C-depleted. The layer of limestone deposited at the Permian extinction 252 Mya can be identified by the 1% drop in
13C/
12C.
The
14C isotope is important in distinguishing
biosynthetized materials from man-made ones.
Biogenic chemicals are derived from biospheric carbon, which contains
14C. Carbon in artificially made chemicals is usually derived from
fossil fuels like
coal
Coal is a combustible black or brownish-black sedimentary rock, formed as rock strata called coal seams. Coal is mostly carbon with variable amounts of other elements, chiefly hydrogen, sulfur, oxygen, and nitrogen.
Coal is formed when ...
or
petroleum
Petroleum, also known as crude oil, or simply oil, is a naturally occurring yellowish-black liquid mixture of mainly hydrocarbons, and is found in geological formations. The name ''petroleum'' covers both naturally occurring unprocessed crud ...
, where the
14C originally present has decayed below detectable limits. The amount of
14C currently present in a sample therefore indicates the proportion of carbon of biogenic origin.
Nitrogen isotopes
Nitrogen-15
Natural nitrogen (7N) consists of two stable isotopes: the vast majority (99.6%) of naturally occurring nitrogen is nitrogen-14, with the remainder being nitrogen-15. Fourteen radioisotopes are also known, with atomic masses ranging from 10 to 25, ...
, or
15N, is often used in
agricultural and
medical
Medicine is the science and practice of caring for a patient, managing the diagnosis, prognosis, prevention, treatment, palliation of their injury or disease, and promoting their health. Medicine encompasses a variety of health care practic ...
research, for example in the
Meselson–Stahl experiment to establish the nature of
DNA replication
In molecular biology, DNA replication is the biological process of producing two identical replicas of DNA from one original DNA molecule. DNA replication occurs in all living organisms acting as the most essential part for biological inheritanc ...
. An extension of this research resulted in development of DNA-based stable-isotope probing, which allows examination of links between
metabolic function and
taxonomic identity of
microorganisms in the environment, without the need for
culture
Culture () is an umbrella term which encompasses the social behavior, institutions, and norms found in human societies, as well as the knowledge, beliefs, arts, laws, customs, capabilities, and habits of the individuals in these groups ...
isolation.
Proteins can be isotopically labelled by cultivating them in a medium containing
15N as the only source of nitrogen, e.g., in quantitative
proteomics such as
SILAC Stable Isotope Labeling by/with Amino acids in Cell culture (SILAC) is a technique based on mass spectrometry that detects differences in protein abundance among samples using non-radioactive isotopic labeling. It is a popular method for quantitativ ...
.
Nitrogen-15 is extensively used to trace
mineral nitrogen compounds (particularly
fertilizers
A fertilizer (American English) or fertiliser (British English; see spelling differences) is any material of natural or synthetic origin that is applied to soil or to plant tissues to supply plant nutrients. Fertilizers may be distinct from ...
) in the environment. When combined with the use of other isotopic labels,
15N is also a very important
tracer for describing the fate of nitrogenous
organic pollutants.
Nitrogen-15 tracing
Nitrogen-15 (15N) tracing is a technique to study the nitrogen cycle using the heavier, stable nitrogen isotope 15 N. Despite the different weights, 15N is involved in the same chemical reactions as the more abundant 14N and is therefore used to t ...
is an important method used in
biogeochemistry
Biogeochemistry is the scientific discipline that involves the study of the chemical, physical, geological, and biological processes and reactions that govern the composition of the natural environment (including the biosphere, the cryosphere, ...
.
The ratio of stable nitrogen isotopes,
15N/
14N or
δ15N, tends to increase with
trophic level
The trophic level of an organism is the position it occupies in a food web. A food chain is a succession of organisms that eat other organisms and may, in turn, be eaten themselves. The trophic level of an organism is the number of steps it ...
, such that
herbivores have higher nitrogen isotope values than
plant
Plants are predominantly photosynthetic eukaryotes of the kingdom Plantae. Historically, the plant kingdom encompassed all living things that were not animals, and included algae and fungi; however, all current definitions of Plantae exclu ...
s, and
carnivore
A carnivore , or meat-eater (Latin, ''caro'', genitive ''carnis'', meaning meat or "flesh" and ''vorare'' meaning "to devour"), is an animal or plant whose food and energy requirements derive from animal tissues (mainly muscle, fat and other s ...
s have higher nitrogen isotope values than herbivores. Depending on the
tissue being examined, there tends to be an increase of 3-4 parts per thousand with each increase in trophic level.
The tissues and
hair of
vegan
Veganism is the practice of abstaining from the use of animal product—particularly in diet—and an associated philosophy that rejects the commodity status of animals. An individual who follows the diet or philosophy is known as a vegan. ...
s therefore contain significantly lower δ
15N than the bodies of people who eat mostly meat. Similarly, a terrestrial diet produces a different signature than a marine-based diet. Isotopic
analysis of hair is an important source of information for
archaeologists, providing clues about the ancient diets and differing cultural attitudes to food sources.
A number of other environmental and physiological factors can influence the nitrogen isotopic composition at the base of the
food web
A food web is the natural interconnection of food chains and a graphical representation of what-eats-what in an ecological community. Another name for food web is consumer-resource system. Ecologists can broadly lump all life forms into one o ...
(i.e. in plants) or at the level of individual animals. For example, in arid regions, the
nitrogen cycle tends to be more 'open' and prone to the loss of
14N, increasing δ
15N in soils and plants.
This leads to relatively high δ
15N values in plants and animals in hot and arid ecosystems relative to cooler and moister ecosystems.
Furthermore, elevated δ
15N have been linked to the preferential excretion of 14N and reutilization of already enriched 15N tissues in the body under prolonged water stress conditions or insufficient protein intake.
δ
15N also provides a diagnostic tool in
planetary science as the ratio exhibited in atmospheres and surface materials "is closely tied to the conditions under which materials form".
Oxygen isotopes
Oxygen comes in three variants, but the
17 O is so rare that it is very difficult to detect (~0.04% abundant).
The ratio of
18O/
16O in water depends on the amount of evaporation the water experienced (as
18O is heavier and therefore less likely to vaporize). As the vapor tension depends on the concentration of dissolved salts, the
18 O/
16O ratio shows correlation on the
salinity and temperature of water. As oxygen gets built into the shells of
calcium carbonate secreting organisms, such sediments prove a chronological record of temperature and salinity of the water in the area.
Oxygen isotope ratio in atmosphere varies predictably with time of year and geographic location; e.g. there is a 2% difference between
18O-rich precipitation in Montana and
18O-depleted precipitation in Florida Keys. This variability can be used for approximate determination of geographic location of origin of a material; e.g. it is possible to determine where a shipment of
uranium oxide
Uranium oxide is an oxide of the element uranium.
The metal uranium forms several oxides:
* Uranium dioxide or uranium(IV) oxide (UO2, the mineral uraninite or pitchblende)
* Diuranium pentoxide or uranium(V) oxide (U2O5)
* Uranium trioxide o ...
was produced. The rate of exchange of surface isotopes with the environment has to be taken in account.
The oxygen isotopic signatures of solid samples (organic and inorganic) are usually measured with
pyrolysis
The pyrolysis (or devolatilization) process is the thermal decomposition of materials at elevated temperatures, often in an inert atmosphere. It involves a change of chemical composition. The word is coined from the Greek-derived elements ''py ...
and
mass spectrometry.
Researchers need to avoid improper or prolonged storage of the samples for accurate measurements.
Sulfur Isotopes
Sulfur has four stable isotopes,
32 S,
33S,
34S, and
36S, of which
32S is the most abundant by a large margin due to the fact it is
created by the very common 12C in supernovas. Sulfur isotope ratios are almost always expressed as ratios relative to
32S due to this major relative abundance (95.0%). Sulfur isotope fractionations are usually measured in terms of
δ34S due to its higher abundance (4.25%) compared to the
other stable isotopes of sulfur, though δ
33S is also sometimes measured. Differences in sulfur isotope ratios are thought to exist primarily due to
kinetic fractionation
Kinetic fractionation is an isotopic fractionation process that separates stable isotopes from each other by their mass during unidirectional processes. Biological processes are generally unidirectional and are very good examples of "kinetic" isot ...
during reactions and transformations.
Sulfur isotopes are generally measured against standards; prior to 1993, the
Canyon Diablo troilite
Troilite is a rare iron sulfide mineral with the simple formula of FeS. It is the iron-rich endmember of the pyrrhotite group. Pyrrhotite has the formula Fe(1-x)S (x = 0 to 0.2) which is iron deficient. As troilite lacks the iron deficiency whic ...
standard (abbreviated to
CDT), which has a
32S:
34S equal to 22.220, was used as both a reference material and the zero point for the isotopic scale. Since 1993, the Vienna-CDT standard has been used as a zero point, and there are several materials used as
reference materials for sulfur isotope measurements. Sulfur fractionations by natural processes measured against these standards have been shown to exist between -72‰ and +147‰,
as calculated by the following equation:
As a very
redox-active element, sulfur can be useful for recording major chemistry-altering events throughout
Earth's history
The history of Earth concerns the development of planet Earth from its formation to the present day. Nearly all branches of natural science have contributed to understanding of the main events of Earth's past, characterized by constant geologic ...
, such as marine
evaporite
An evaporite () is a water- soluble sedimentary mineral deposit that results from concentration and crystallization by evaporation from an aqueous solution. There are two types of evaporite deposits: marine, which can also be described as ocean ...
s which reflect the change in the atmosphere's redox state brought about by the
Oxygen Crisis.
Radiogenic isotopes
Lead isotopes
Lead consists of four stable
isotopes
Isotopes are two or more types of atoms that have the same atomic number (number of protons in their nuclei) and position in the periodic table (and hence belong to the same chemical element), and that differ in nucleon numbers (mass numbers) ...
:
204Pb,
206Pb,
207Pb, and
208Pb. Local variations in
uranium
Uranium is a chemical element with the symbol U and atomic number 92. It is a silvery-grey metal in the actinide series of the periodic table. A uranium atom has 92 protons and 92 electrons, of which 6 are valence electrons. Uranium is weak ...
/
thorium
Thorium is a weakly radioactive metallic chemical element with the symbol Th and atomic number 90. Thorium is silvery and tarnishes black when it is exposed to air, forming thorium dioxide; it is moderately soft and malleable and has a high ...
/
lead
Lead is a chemical element with the symbol Pb (from the Latin ) and atomic number 82. It is a heavy metal that is denser than most common materials. Lead is soft and malleable, and also has a relatively low melting point. When freshly cu ...
content cause a wide location-specific variation of isotopic ratios for lead from different localities. Lead emitted to the atmosphere by industrial processes has an isotopic composition different from lead in minerals. Combustion of
gasoline
Gasoline (; ) or petrol (; ) (see ) is a transparent, petroleum-derived flammable liquid that is used primarily as a fuel in most spark-ignited internal combustion engines (also known as petrol engines). It consists mostly of organi ...
with
tetraethyllead
Tetraethyllead (commonly styled tetraethyl lead), abbreviated TEL, is an organolead compound with the formula Pb( C2H5)4. It is a fuel additive, first being mixed with gasoline beginning in the 1920s as a patented octane rating booster that ...
additive led to formation of ubiquitous micrometer-sized lead-rich
particulate
Particulates – also known as atmospheric aerosol particles, atmospheric particulate matter, particulate matter (PM) or suspended particulate matter (SPM) – are microscopic particles of solid or liquid matter suspended in the air. The te ...
s in car exhaust
smoke
Smoke is a suspension of airborne particulates and gases emitted when a material undergoes combustion or pyrolysis, together with the quantity of air that is entrained or otherwise mixed into the mass. It is commonly an unwanted by-produc ...
; especially in urban areas the man-made lead particles are much more common than natural ones. The differences in isotopic content in particles found in objects can be used for approximate geolocation of the object's origin.
Radioactive isotopes
Hot particle
A hot particle is a microscopic piece of radioactive material that can become lodged in living tissue and deliver a concentrated dose of radiation to a small area. A controversial theory proposes that hot particles within the body are vastly more ...
s, radioactive particles of
nuclear fallout
Nuclear fallout is the residual radioactive material propelled into the upper atmosphere following a nuclear blast, so called because it "falls out" of the sky after the explosion and the shock wave has passed. It commonly refers to the radioac ...
and
radioactive waste
Radioactive waste is a type of hazardous waste that contains radioactive material. Radioactive waste is a result of many activities, including nuclear medicine, nuclear research, nuclear power generation, rare-earth mining, and nuclear weapons r ...
, also exhibit distinct isotopic signatures. Their radionuclide composition (and thus their age and origin) can be determined by
mass spectrometry or by
gamma spectrometry. For example, particles generated by a nuclear blast contain detectable amounts of
60 Co and
152 Eu. The
Chernobyl accident did not release these particles but did release
125 Sb and
144 Ce. Particles from underwater bursts will consist mostly of irradiated sea salts. Ratios of
152 Eu/
155Eu,
154Eu/
155Eu, and
238 Pu/
239Pu are also different for fusion and fission
nuclear weapon
A nuclear weapon is an explosive device that derives its destructive force from nuclear reactions, either fission (fission bomb) or a combination of fission and fusion reactions ( thermonuclear bomb), producing a nuclear explosion. Both bom ...
s, which allows identification of hot particles of unknown origin.
Uranium has a relatively constant isotope ratio in all natural samples with ~0.72% some 55
ppm (in
secular equilibrium
In nuclear physics, secular equilibrium is a situation in which the quantity of a radioactive isotope remains constant because its production rate (e.g., due to decay of a parent isotope) is equal to its decay rate.
In radioactive decay
Secular e ...
with its
parent nuclide
In nuclear physics, a decay product (also known as a daughter product, daughter isotope, radio-daughter, or daughter nuclide) is the remaining nuclide left over from radioactive decay. Radioactive decay often proceeds via a sequence of steps (de ...
) and the balance made up by . Isotopic compositions that diverge significantly from those values are evidence for the uranium having been subject to depletion or
enrichment in some fashion or of (part of it) having participated in a nuclear fission reaction. While the latter is almost as universally due to human influence as the former two, the
natural nuclear fission reactor
A natural nuclear fission reactor is a uranium deposit where self-sustaining nuclear chain reactions occur. The conditions under which a natural nuclear reactor could exist had been predicted in 1956 by Japanese American chemist Paul Kuroda. ...
at
Oklo
Oklo is a region near the town of Franceville, in the Haut-Ogooué province of the Central African country of Gabon. Several natural nuclear fission reactors were discovered in the uranium mines in the region in 1972.
History
Gabon was a Fren ...
, Gabon was detected through a significant diversion of concentration in samples from Oklo compared to those of all other known deposits on earth. Given that is a
material of proliferation concern then as now every
IAEA
The International Atomic Energy Agency (IAEA) is an intergovernmental organization that seeks to promote the peaceful use of nuclear energy and to inhibit its use for any military purpose, including nuclear weapons. It was established in 195 ...
-approved supplier of Uranium fuel keeps track of the isotopic composition of uranium to ensure none is diverted for nefarious purposes. It would thus become apparent quickly if another Uranium deposit besides Oklo proves to have once been a natural nuclear fission reactor.
Applications
Archaeological studies
In archaeological studies, stable isotope ratios have been used to track diet within the time span formation of analyzed tissues (10–15 years for bone collagen and intra-annual periods for tooth enamel bioapatite) from individuals; "recipes" of foodstuffs (ceramic vessel residues); locations of cultivation and types of plants grown (chemical extractions from sediments); and migration of individuals (dental material).
Forensics
With the advent of stable
isotope ratio mass spectrometry, isotopic signatures of materials find increasing use in
forensics, distinguishing the origin of otherwise similar materials and tracking the materials to their common source. For example, the isotope signatures of plants can be to a degree influenced by the growth conditions, including moisture and nutrient availability. In case of synthetic materials, the signature is influenced by the conditions during the chemical reaction. The isotopic signature profiling is useful in cases where other kinds of profiling, e.g. characterization of
impurities, are not optimal. Electronics coupled with scintillator detectors are routinely used to evaluate isotope signatures and identify unknown sources.
A study was published demonstrating the possibility of determination of the origin of a common brown
PSA packaging tape by using the carbon, oxygen, and hydrogen isotopic signature of the backing polymer, additives, and
adhesive.
Measurement of carbon isotopic ratios can be used for detection of
adulteration
An adulterant is caused by the act of adulteration, a practice of secretly mixing a substance with another. Typical substances that are adulterated include but are not limited to food, cosmetics, pharmaceuticals, fuel, or other chemicals, that ...
of
honey
Honey is a sweet and viscous substance made by several bees, the best-known of which are honey bees. Honey is made and stored to nourish bee colonies. Bees produce honey by gathering and then refining the sugary secretions of plants (primar ...
. Addition of sugars originated from corn or sugar cane (C4 plants) skews the isotopic ratio of sugars present in honey, but does not influence the isotopic ratio of proteins; in an unadulterated honey the carbon isotopic ratios of sugars and proteins should match. As low as 7% level of addition can be detected.
Nuclear explosions form
10Be by a reaction of fast neutrons with
13C in the carbon dioxide in air. This is one of the historical indicators of past activity at nuclear test sites.
Solar system origins
Isotopic fingerprints are used to study the origin of materials in the Solar System.
[ For example, the ]Moon
The Moon is Earth's only natural satellite. It is the fifth largest satellite in the Solar System and the largest and most massive relative to its parent planet, with a diameter about one-quarter that of Earth (comparable to the width of ...
's oxygen isotopic ratios seem to be essentially identical to Earth's. Oxygen isotopic ratios, which may be measured very precisely, yield a unique and distinct signature for each solar system body. Different oxygen isotopic signatures can indicate the origin of material ejected into space. The Moon's titanium isotope
Naturally occurring titanium (22Ti) is composed of five stable isotopes; 46Ti, 47Ti, 48Ti, 49Ti and 50Ti with 48Ti being the most abundant (73.8% natural abundance). Twenty-one radioisotopes have been characterized, with the most stable being 44Ti ...
ratio (50Ti/47Ti) appears close to the Earth's (within 4 ppm). In 2013, a study was released that indicated water in lunar magma was 'indistinguishable' from carbonaceous chondrites and nearly the same as Earth's, based on the composition of water isotopes.
Records of Early Life on Earth
Isotope biogeochemistry has been used to investigate the timeline surrounding life and its earliest iterations on Earth. Isotopic fingerprints typical of life, preserved in sediments, have been used to suggest, but do not necessarily prove, that life was already in existence on Earth by 3.85 billion years ago.
Sulfur isotope evidence has also been used to corroborate the timing of the Great Oxidation Event
The Great Oxidation Event (GOE), also called the Great Oxygenation Event, the Oxygen Catastrophe, the Oxygen Revolution, the Oxygen Crisis, or the Oxygen Holocaust, was a time interval during the Paleoproterozoic era when the Earth's atmosphere ...
, during which the Earth's atmosphere
The atmosphere of Earth is the layer of gases, known collectively as air, retained by Earth's gravity that surrounds the planet and forms its planetary atmosphere. The atmosphere of Earth protects life on Earth by creating pressure allowing fo ...
experienced a measurable rise in oxygen (to about 9% of modern values) for the first time about 2.3-2.4 billion years ago. Mass-independent sulfur isotope fractionations are found to be widespread in the geologic record before about 2.45 billion years ago, and these isotopic signatures have since ceded to mass-dependent fractionation, providing strong evidence that the atmosphere shifted from anoxic to oxygenated at that threshold.
Modern sulfate-reducing bacteria
Sulfate-reducing microorganisms (SRM) or sulfate-reducing prokaryotes (SRP) are a group composed of sulfate-reducing bacteria (SRB) and sulfate-reducing archaea (SRA), both of which can perform anaerobic respiration utilizing sulfate () as termina ...
are known to favorably reduce lighter 32S instead of 34S, and the presence of these microorganisms can measurably alter the sulfur isotope composition of the ocean. Because the δ34S values of sulfide mineral
The sulfide minerals are a class of minerals containing sulfide (S2−) or disulfide (S22−) as the major anion. Some sulfide minerals are economically important as metal ores. The sulfide class also includes the selenides, the tellurides, th ...
s is primarily influenced by the presence of sulfate-reducing bacteria
Sulfate-reducing microorganisms (SRM) or sulfate-reducing prokaryotes (SRP) are a group composed of sulfate-reducing bacteria (SRB) and sulfate-reducing archaea (SRA), both of which can perform anaerobic respiration utilizing sulfate () as termina ...
, the absence of sulfur isotope fractionations in sulfide minerals suggests the absence of these bacterial processes or the absence of freely available sulfate. Some have used this knowledge of microbial sulfur fractionation to suggest that minerals (namely pyrite
The mineral pyrite (), or iron pyrite, also known as fool's gold, is an iron sulfide with the chemical formula Fe S2 (iron (II) disulfide). Pyrite is the most abundant sulfide mineral.
Pyrite's metallic luster and pale brass-yellow hue giv ...
) with large sulfur isotope fractionations relative to the inferred seawater composition may be evidence of life. This claim is not clear-cut, however, and is sometimes contested using geologic evidence from the ~3.49 Ga sulfide mineral
The sulfide minerals are a class of minerals containing sulfide (S2−) or disulfide (S22−) as the major anion. Some sulfide minerals are economically important as metal ores. The sulfide class also includes the selenides, the tellurides, th ...
s found in the Dresser Formation
The Pilbara Craton is an old and stable part of the continental lithosphere located in the Pilbara region of Western Australia.
The Pilbara Craton is one of only two pristine Archean, Archaean 3.6–2.7 Gigaannum, Ga (billion years ago) crusts ...
of Western Australia, which are found to have δ34S values as negative as -22‰. Because it has not been proven that the sulfide and barite minerals formed in the absence of major hydrothermal input, it is not conclusive evidence of life or of the microbial sulfate reduction pathway in the Archean.
See also
*Isoscapes An isoscape is a geologic map of isotope distribution. It is a spatially explicit prediction of elemental isotope ratios (δ) that is produced by executing process-level models of elemental isotope fractionation or distribution in a geographic in ...
* Isotope electrochemistry
*Isotope geochemistry
Isotope geochemistry is an aspect of geology based upon the study of natural variations in the relative abundances of isotopes of various elements. Variations in isotopic abundance are measured by isotope ratio mass spectrometry, and can reveal ...
*Radiometric dating
Radiometric dating, radioactive dating or radioisotope dating is a technique which is used to date materials such as rocks or carbon, in which trace radioactive impurities were selectively incorporated when they were formed. The method compares ...
References
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Further reading
Carbon isotopes: you are what you eat
Ayacucho Archaeo Isotope Project
The pursuit of isotopic and molecular fire tracers in the polar atmosphere and cryosphere
Radiometric dating
Bioindicators
Anthropology
Isotopes
Forensic evidence