Editing Geophysics (section)

=== Radioactivity ===
{{further|Radiometric dating}}
[[Image:Thorium decay chain from lead-212 to lead-208.svg|thumb|Example of a radioactive decay chain (see [[Radiometric dating]]) |alt=Diagram with compound balls representing nuclei and arrows.]]
[[Radioactive decay]] accounts for about 80% of the Earth's [[internal heat]], powering the geodynamo and plate tectonics.<ref name=Turcotte>{{harvnb|Turcotte|Schubert|2002}}</ref> The main heat-producing [[isotopes]] are [[Potassium|potassium-40]], [[Uranium|uranium-238]], uranium-235, and [[Thorium|thorium-232]].<ref>{{harvnb|Sanders|2003}}</ref>
Radioactive elements are used for [[radiometric dating]], the primary method for establishing an absolute time scale in [[geochronology]].

Unstable isotopes decay at predictable rates, and the decay rates of different [[isotope]]s cover several orders of magnitude, so radioactive decay can be used to accurately date both recent events and events in past [[Era (geology)|geologic eras]].<ref name=Renne>{{harvnb|Renne|Ludwig|Karner|2000}}</ref> Radiometric mapping using ground and airborne [[gamma spectrometry]] can be used to map the concentration and distribution of radioisotopes near the Earth's surface, which is useful for mapping lithology and alteration.<ref>{{cite web|title=Radiometrics|url=http://www.ga.gov.au/scientific-topics/disciplines/geophysics/radiometrics|website=Geoscience Australia|date=15 May 2014|publisher=Commonwealth of Australia|access-date=23 June 2014}}</ref><ref>{{cite web|title=Interpreting radiometrics|url=http://spatial.agric.wa.gov.au/geophysics/radiometrics.asp|archive-url=https://web.archive.org/web/20120321102348/http://spatial.agric.wa.gov.au/geophysics/radiometrics.asp |archive-date=21 March 2012|website=Natural Resource Management|publisher=Department of Agriculture and Food, Government of Western Australia|access-date=23 June 2014}}</ref>