Uranium 238 dating rocks
Each of them typically exists in igneous rock, or rock made from cooled magma.
Fossils, however, form in sedimentary rock -- sediment quickly covers a dinosaur's body, and the sediment and the bones gradually turn into rock.
By using radiometric dating to determine the age of igneous brackets, researchers can accurately determine the age of the sedimentary layers between them.
It is now known that uranium, radioactive in all its isotopes, consists naturally of a mixture of uranium-238 (99.27 percent, 4,510,000,000-year half-life), uranium-235 (0.72 percent, 713,000,000-year half-life), and uranium-234 (0.006 percent, 247,000-year half-life). Uranium-238 and thorium-232 (and some other fissionable materials) cannot maintain a self-sustaining fission explosion, but these isotopes can be made to fission by an externally maintained supply of fast neutrons from fission or fusion reactions.
Thus, the yield of a nuclear weapon can be increased by surrounding the device with uranium-238, in the form of either natural or depleted uranium,...
Absorption of a neutron in the uranium-238 nucleus yields uranium-239, which decays after 23.47 minutes through electron emission into neptunium-239 and ultimately, after 2.356 days, into plutonium-239. The principal value of uranium is in the radioactive and fissionable properties of its isotopes.
In nature, almost all (99.27 percent) of the metal consists of uranium-238; the remainder consists of uranium-235 (0.72 percent) and uranium-234 (0.006 percent).