Isotope geochemistry is an aspect of geology based upon study of the relative and absolute concentrations of the elements and their isotopes in the Earth. Broadly, the field is divided into two branches: stable and radiogenic isotope geochemistry. Geology (from Greek γη- (ge-, the earth) and λογος (logos, word, reason)) is the science and study of the Earth, its composition, structure, physical properties, history and the processes that shape it. ... A chemical element, often called simply element, is a chemical substance that cannot be divided or changed into other chemical substances by any ordinary chemical technique. ... Isotopes are atoms of a chemical element whose nuclei have the same atomic number, Z, but different atomic weights, A. The word isotope, meaning at the same place, comes from the fact that isotopes are located at the same place on the periodic table. ... Earth is the third planet in the solar system. ... This article needs to be cleaned up to conform to a higher standard of quality. ... A radiogenic nuclide is one that is produced by a process of radioactive decay. ...

Lead-Lead Isotope Geochemistry

Lead has four stable isotopes - ²⁰⁴Pb, ²⁰⁶Pb, ²⁰⁷Pb, ²⁰⁸Pb and one common radiogenic isotope ²⁰²Pb with a half-life of ~53,000 years. General Name, Symbol, Number lead, Pb, 82 Chemical series poor metals Group, Period, Block 14, 6, p Appearance bluish white Atomic mass 207. ... Isotopes are atoms of a chemical element whose nuclei have the same atomic number, Z, but different atomic weights, A. The word isotope, meaning at the same place, comes from the fact that isotopes are located at the same place on the periodic table. ... Half-Life For a quantity subject to exponential decay, the half-life is the time required for the quantity to fall to half of its initial value. ...

Lead is created in the Earth via decay of transuranic elements, primarily uranium and thorium. In chemistry, transuranium elements (also known as transuranic elements) are the chemical elements with atomic numbers greater than 92, the atomic number of Uranium. ... Generally, an element is a basic part that is the foundation of something. ... General Name, Symbol, Number uranium, U, 92 Chemical series actinides Group, Period, Block n/a, 7, f Appearance silvery gray metallic; corrodes to a spalling black oxide coat in air Atomic mass 238. ... General Name, Symbol, Number thorium, Th, 90 Chemical series Actinides Group, Period, Block n/a, 7, f Appearance silvery white Atomic mass 232. ...

Lead isotope geochemistry is useful for providing isotopic dates on a variety of materials. Because the lead isotopes are created by decay of different transuranic elements, the ratios of the four lead isotopes to one another can be very useful in tracking the source of melts in igneous rocks, the source of sediments and even the origin of people via isotopic fingerprinting of their teeth, skin and bones. The field of geochemistry involves study of the chemical composition of the Earth and other planets, chemical processes and reactions that govern the composition of rocks and soils, and the cycles of matter and energy that transport the Earths chemical components in time and space, and their interaction with... Radiometric dating is a technique used to date materials based on a knowledge of the decay rates of naturally occurring isotopes, and the current abundances. ... Igneous rocks are formed when molten rock (magma) cools and solidifies, with or without crystallization, either below the surface as intrusive (plutonic) rocks or on the surface as extrusive (volcanic) rocks. ... Sediment is any particulate matter that can be transported by fluid flow and which eventually is deposited as a layer of solid particles on the bed or bottom of a body of water or other liquid. ...

It has been used to date ice cores from the Arctic shelf, and provides information on the source of atmospheric lead pollution. Ice Core sample taken from drill. ... This power plant in New Mexico releases sulfur dioxide and particulate matter into the air. ...

Lead-lead isotopes has been successfully used in forensic science to fingerprint bullets, because each batch of ammunition has its own peculiar ²⁰⁴Pb/²⁰⁶Pb vs ²⁰⁷Pb/²⁰⁸Pb ratio. Forensics or forensic science is the application of science to questions which are of interest to the legal system. ...

Samarium-Neodymium

Main article: Samarium-neodymium dating

Samarium-Neodymium is an isotope system which can be utilised to provide a date as well as isotopic fingerprints of geological materials, and various other materials including archaeological finds (pots, ceramics). This article needs to be cleaned up to conform to a higher standard of quality. ... General Name, Symbol, Number Samarium, Sm, 62 Chemical series Lanthanides Group, Period, Block _ , 6 , f Density, Hardness 7353 kg/m3, no data Appearance silvery white Atomic properties Atomic weight 150. ... General Name, Symbol, Number neodymium, Nd, 60 Chemical series lanthanides Group, Period, Block ?, 6, f Appearance silvery white, yellowish tinge Atomic mass 144. ...

¹⁴⁷Sm decays to produce ¹⁴³Nd with a half life of 1.06x10¹¹ years.

Dating is achieved usually by achieving an isochron of several minerals within a rock specimen. The initial ¹⁴³Nd/¹⁴⁸Nd ratio is determined. Iscochron dating is a type of radiometric dating. ...

The initial Nd/Nd ratio is modelled relative to CHUR - the Chondritic Uniform Reservoir - which is an approximation of the chondritic material which formed the solar system. CHUR was determined by analysing chondrite and achondrite meteorites. Chondrites are meteorites of the stony type, that have not been modified due to melting or differentiation of the parent body. ... An Achondrite is a stony meteorite that is made of material similar to terrestrial basalts or plutonic rocks. ...

The difference in the ratio of the sample relative to CHUR can give information on a model age of extraction from the mantle (for which an assumed evolution has been calculated relative to CHUR) and to whether this was extracted from a granitic source (depleted in radiogenic Nd), the mantle, or an enriched source.

Rhenium-Osmium

Rhenium and osmium are chalcophile elements which are present at very low abundances in the crust. Rhenium undergoes radioactive decay to produce osmium. The ratio of non-radiogenic osmium to radiogenic osmium throughout time varies. General Name, Symbol, Number rhenium, Re, 75 Chemical series transition metals Group, Period, Block 7, 6, d Appearance grayish white Atomic mass 186. ... General Name, Symbol, Number osmium, Os, 76 Chemical series transition metals Group, Period, Block 8, 6, d Appearance silvery, blue cast Atomic mass 190. ... Radioactive decay is the set of various processes by which unstable atomic nuclei (nuclides) emit subatomic particles (radiation). ...

Rhenium prefers to enter sulfides more readily than osmium. Hence, during melting of the mantle, rhenium is stripped out, and prevents the osmium-osmium ratio from changing appreciably. This locks in an initial osmium ratio of the sample at the time of the melting event. Osmium-osmium initial ratios are used to determine the source characteristic and age of mantle melting events. The term sulfide (sulphide in British) refers to several types of chemical compounds containing sulfur in its lowest oxidation number of -2. ...

Noble Gas Isotopes

Helium-3

Helium-3 was trapped in the planet when it was created. Some ³He is being added by meteoric dust, primarily collecting on the bottom of oceans (although due to subduction, all oceanic tectonic plates are younger than continental plates). However, ³He will be degassed from oceanic sediment during subduction, so cosmogenic ³He is not affecting the concentration or noble gas ratios of the mantle. Helium-3 is a non-radioactive and light isotope of helium. ... Subduction zones mark sites of convective downwelling of the Earths lithosphere. ... The tectonic plates of the world were mapped in the second half of the 20th century. ... Subduction zones mark sites of convective downwelling of the Earths lithosphere. ... The noble gases are the chemical elements in group 18 (old-style Group 0) of the periodic table. ... Earth cutaway from core to exosphere. ...

Helium-3 is created by cosmic ray bombardment, and by lithium spallation reactions which generally occur in the crust. Lithium spallation is the process by which a high-energy neutron bombards a lithium atom, creating a ³He and a ⁴He ion. This requires significant lithium to adversely affect the ³He/⁴He ratio. Cosmic rays can loosely be defined as energetic particles originating outside of the Earth. ... General Name, Symbol, Number lithium, Li, 3 Chemical series alkali metals Group, Period, Block 1, 2, s Appearance silvery white/gray Atomic mass 6. ... In nuclear physics, spallation is the process in which a heavy nucleus emits a large number of nucleons as a result of being hit by a high-energy proton, thus greatly reducing its atomic weight. ... A fast neutron is a free neutron with a kinetic energy level close to 1 MeV (10 TJ/kg, hence a speed of 14,000 km/s. ... General Name, Symbol, Number lithium, Li, 3 Chemical series alkali metals Group, Period, Block 1, 2, s Appearance silvery white/gray Atomic mass 6. ...

All degassed helium is lost to space eventually, due to the escape velocity of helium exceeding that of Earth. Thus, it is assumed the helium content and ratios of Earth's atmosphere have remained essentially stable. Layers of Atmosphere (NOAA) Earths atmosphere is a layer of gases surrounding the planet Earth and retained by the Earths gravity. ...

It has been observed that ³He is present in volcano emissions and oceanic ridge samples. How ³He is stored in the planet is under investigation, but it is associated with the mantle and is used as a marker of material of deep origin. A volcano is a geological landform usually generated by the eruption through a planets surface of magma, molten rock welling up from the planets interior. ... An oceanic ridge is an underwater mountain range, usually formed by plate tectonics. ... Earth cutaway from core to exosphere. ...

Due to similarities in helium and carbon in magma chemistry, outgassing of helium requires the loss of volatile components (water, carbon dioxide) from the mantle, which happens at depths of less than 60 km. However, ³He is transported to the surface primarily trapped in the crystal lattice of minerals within fluid inclusions. General Name, Symbol, Number helium, He, 2 Chemical series noble gases Group, Period, Block 18, 1, s Appearance colorless Atomic mass 4. ... General Name, Symbol, Number carbon, C, 6 Chemical series nonmetals Group, Period, Block 14, 2, p Appearance black (graphite) colorless (diamond) Atomic mass 12. ... Magma is molten rock located beneath the surface of the Earth (or any other rocky planet), and which often collects in a magma chamber. ... Volatile is the name of more than one concept: A financial instrument with high volatility is considered volatile in economics. ... A girl in a swimming pool Water (from the Old English waeter; c. ... Carbon dioxide is an atmospheric gas comprised of one carbon and two oxygen atoms. ... It has been suggested that crystallization processes be merged into this article or section. ... Trapped in a time capsule the same size as the diameter of a human hair, the ore-forming liquid in this inclusion was so hot and contained so much dissolved solids that when it cooled, crystals of halite, sylvite, gypsum, and hematite formed. ...

Helium-4 is created by radiogenic production (by decay of uranium/thorium-series elements). The continental crust has become enriched with those elements relative to the mantle and thus more He⁴ is produced in the crust than in the mantle. A radiogenic nuclide is one that is produced by a process of radioactive decay. ... General Name, Symbol, Number uranium, U, 92 Chemical series actinides Group, Period, Block n/a, 7, f Appearance silvery gray metallic; corrodes to a spalling black oxide coat in air Atomic mass 238. ... General Name, Symbol, Number thorium, Th, 90 Chemical series Actinides Group, Period, Block n/a, 7, f Appearance silvery white Atomic mass 232. ... A chemical element, often called simply element, is a chemical substance that cannot be divided or changed into other chemical substances by any ordinary chemical technique. ... The continental crust is the layer of granitic, sedimentary and metamorphic rocks which form the continents and the areas of shallow seabed close to their shores, known as continental shelves. ...

The ratio (R) of ³He to ⁴He is often used to represent ³He content. R usually is given as a multiple of the present atmospheric ratio (Ra).

Common values for R/Ra:

• Old continental crust: less than 1
• mid-ocean ridge basalt (MORB): 7 to 9
• Spreading ridge rocks: 9.1 plus or minus 3.6
• Hotspot rocks: 5 to 42
• Ocean and terrestrial water: 1
• Sedimentary formation water: less than 1
• Thermal spring water: 3 to 11

³He/⁴He isotope chemistry is being used to date groundwaters, estimate groundwater flow rates, track water pollution, and provide insights into hydrothermal processes, igneous geology and ore genesis. An oceanic ridge is an underwater mountain range, usually formed by plate tectonics. ... Basalt Basalt is a common gray to black volcanic rock. ... In geology, a hotspot is a location on the Earths surface that has experienced active volcanism for a long period of time. ... Groundwater is water located beneath the ground surface in soil pore spaces and in the fractures of geologic formations. ... Hydrothermal circulation in the oceans is the passage of the water through mid-ocean Ridge (MOR) systems. ... Igneous rocks are formed when molten rock (magma) cools and solidifies, with or without crystallization, either below the surface as intrusive (plutonic) rocks or on the surface as extrusive (volcanic) rocks. ... Geology (from Greek γη- (ge-, the earth) and λογος (logos, word, reason)) is the science and study of the Earth, its composition, structure, physical properties, history and the processes that shape it. ... The various theories of ore genesis explain how the various types of mineral deposits form within the Earths crust. ...

• (U-Th)/He dating of apatite as a thermal history tool
• USGS: Helium Discharge at Mammoth Mountain Fumarole (MMF)

Ground water isotopes

Tritium/Helium-3

Tritium was released to the atmosphere during atmospheric testing of nuclear bombs. Radioactive decay of tritium produces the noble gas helium-3. Comparing the ratio of tritium to helium-3 (³H/³He) allows estimation of the age of recent ground waters. Tritium (symbol T or 3H) is a radioactive isotope of hydrogen. ... Helium-3 is a non-radioactive and light isotope of helium. ... Groundwater is any water found below the land surface. ...

• USGS Tritium/Helium-3 Dating
• Hydrologic Isotope Tracers - Helium

See also

• Radiometric dating
• Isotopic signature
• Cosmogenic isotopes
• Geochemistry

Radiometric dating is a technique used to date materials based on a knowledge of the decay rates of naturally occurring isotopes, and the current abundances. ... An isotopic signature (also isotopic fingerprint) is a ratio of stable or unstable isotopes of particular elements found in an investigated material. ... Cosmogenic isotopes are rare radioactive isotopes created when cosmic radiation interacts with an atomic nucleus. ... The field of geochemistry involves study of the chemical composition of the Earth and other planets, chemical processes and reactions that govern the composition of rocks and soils, and the cycles of matter and energy that transport the Earths chemical components in time and space, and their interaction with...

General online stable isotope references

• USGS: Stable Isotopes and Mineral Resource Investigations in the United States
• USGS: Fundamentals of Stable Isotope Geochemistry
• Environmental Isotopes
• Fundamentals of Isotope Geochemistry

References

³He/⁴He
Burnard P.G., Farley K.A., & Turner G., 1998. Multiple fluid pulses in a Samoan harzburgite. Chemical Geology, 147, pp. 99-114.

Kirstein L. & Timmerman M., 2000. Evidence of the proto-Iceland lume in northwestern Ireland at 42Ma from helium isotopes. Journal of the Geophysical Society, London. Vol 157, pp. 923-927.

Porcelli D. & Halliday A.N., 2001. The core as a possible source of mantle helium. Earth and Planetary Science Letters, 192, pp. 45-56.

Re-Os
Arne D., Bierlein F.P., Morgan J.W., & Stein H.J., 2001. Re-Os Dating of Sulfides Associated with gold mineralisation in central Victoria, Australia. Economic Geology, 96, pp. 1455-1459. General Name, Symbol, Number gold, Au, 79 Chemical series transition metals Group, Period, Block 11, 6, d Appearance metallic yellow Atomic mass 196. ...

Martin C., 1991. Osmium isotopic characteristics of mantle-derived rocks. Geochimica et Cosmochimica Acta, 55, pp. 1421-1434.