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. 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. ... Generally, an element is a basic part that is the foundation of something. ... 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, also known as the Earth or Terra, is the third planet outward from the Sun. ...

Magmatic isotopes

Helium-3

Helium-3 was trapped in the planet when it was created. Some He-3 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). Helium-3 is a non-radioactive and light isotope of helium. ... Categories: Geology stubs | Plate tectonics ... The tectonic plates of the world were mapped in the second half of the 20th century. ...

It has been observed that He-3 is present in volcano emissions and oceanic ridge samples. How He-3 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. This article is about volcanoes in geology. ... An oceanic ridge is an underwater mountain range, usually formed by plate tectonics. ... The mantle is the layer in the structure of the Earth that lies directly under the Earths crust. ...

Due to similiarities in helium and carbon in magma chemistry, outgassing of helium requires bubbling of carbon dioxide, which happens at depths of less than 60 km. General Name, Symbol, Number Helium, He, 2 Atomic weight 4. ... General Name, Symbol, Number Carbon, C, 6 Chemical series Nonmetals Group, Period, Block 14 (IVA), 2, p Density, Hardness 2267 kg/m3 0. ... This article is about the type of rock. ... Carbon dioxide is an atmospheric gas composed of one carbon and two oxygen atoms. ...

Helium-4 is created by radiogenic production (by decay of Uranium/Thorium-series elements). Due to crystallization of U/Th-series elements, the continental crust has become enriched with those elements and more He-4 is produced in the crust than in the mantle. The mantle is believed to have a lower ratio of He-3 to He-4 than the crust. A radiogenic nuclide is one that is produced by a process of radioactive decay. ... General Name, Symbol, Number Uranium, U, 92 Chemical series Actinides Period, Block 7 , f Density, Hardness 19050 kg/m3, ND Appearance silvery-white metal Atomic properties Atomic weight 238. ... General Name, Symbol, Number thorium, Th, 90 Chemical series Transition metals Period, Block 7 , f Density, Hardness 11724 kg/m3, 3. ... Generally, an element is a basic part that is the foundation of something. ... The Continental Crust is the layer of granitic and sedimentary rock which forms the continents and the areas of shallow seabed close to their shores, known as continental shelves. ...

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

Common values for R/Ra:

• Continental plate rocks: 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

• (U-Th)/He dating of apatite as a thermal history tool (http://www.geotrack.com.au/uthhe/u-th-he-techinfo.htm)
• USGS: Helium Discharge at Mammoth Mountain Fumarole (MMF) (http://lvo.wr.usgs.gov/helium.html)

An oceanic ridge is an underwater mountain range, usually formed by plate tectonics. ... Basalt Basalt is an extrusive igneous rock, sometimes porphyritic, and is often both fine-grained and dense. ... In geology, a hotspot is a location on the Earths surface that has experienced active vulcanism for a long period of time. ...

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 allows estimation of the age of recent ground waters. Tritium (symbol T or 3H) is an isotope of hydrogen. ... Helium-3 is a non-radioactive and light isotope of helium. ...

• USGS Tritium/Helium-3 Dating (http://water.usgs.gov/lab/3h3he/background/)
• Hydrologic Isotope Tracers - Helium (http://wwwrcamnl.wr.usgs.gov/isoig/period/he_iig.html)

General online stable isotope references

• USGS: Stable Isotopes and Mineral Resource Investigations in the United States (http://pubs.usgs.gov/info/seal2/)
• USGS: Fundamentals of Stable Isotope Geochemistry (http://wwwrcamnl.wr.usgs.gov/isoig/res/funda.html)
• Environmental Isotopes (http://www.science.uottawa.ca/~eih/ch1/ch1.htm)
• Fundamentals of Isotope Geochemistry (http://wwwrcamnl.wr.usgs.gov/isoig/isopubs/itchch2.html)