uranium-thorium-lead dating
- uranium-thorium-lead dating
-
or common-lead dating
Method of dating very old rocks by means of the amount of common lead they contain.
Common lead is any lead from a rock or mineral that contains a large amount of lead and a small amount of the radioactive precursors of lead (i.e., the isotopes uranium-235, uranium-238, and thorium-232). By this method, the age of the Earth has been estimated to be с 4.6 billion years. This figure is in good agreement with the age of meteorites and the age of the Moon as determined independently.
* * *
also called Common-lead Dating,
method of establishing the time of origin of a rock by means of the amount of common lead it contains; common lead is any lead from a rock or mineral that contains a large amount of lead and a small amount of the radioactive progenitors of lead—i.e., the uranium isotopes uranium-235 and uranium-238 and the thorium isotope thorium-232.
The important characteristic of common lead is that it contains no significant proportion of radiogenic lead accumulated since the time that the mineral or rock phase was formed. Of the four isotopes of lead, two are formed from the uranium isotopes and one is formed from the thorium isotope; only lead-204 is not known to have any long-lived radioactive progenitor. Primordial lead is thought to have been formed by stellar nuclear reactions, released to space by supernovae explosions, and incorporated within the dust cloud that constituted the primordial solar system; the troilite (iron sulfide) phase of iron meteorites contains lead that approximates the primordial composition. The lead incorporated within the Earth has been evolving continuously from primordial lead and from the radioactive decay of uranium and thorium isotopes. Thus, the lead isotopic composition of any mineral or rock depends upon its age and the environment from which it was formed; that is, it would depend upon the ratio of uranium plus thorium to lead in the parent material.
The Earth can be assumed to be a very large sample containing lead evolving from primordial lead by radiogenic increments. If modern lead, for example, from marine sediments or modern basalts has the composition of lead in the Earth and if the lead in the troilite phase of iron meteorites has the composition of primordial lead, then a simple model yields about 4.6 billion years for the age of the Earth. This age is in good agreement with the age of the meteorites and the age of the Moon as determined independently.
* * *
Universalium.
2010.
Look at other dictionaries:
Uranium-thorium dating — Uranium thorium dating, also called thorium 230 dating, uranium series disequilibrium dating or uranium series dating, is a radiometric dating technique commonly used to determine the age of carbonate materials such as speleothem or coral [ [http … Wikipedia
Uranium-lead dating — Uranium lead is one of the oldest and most refined radiometric dating schemes, with a routine age range of about 1 million years to over 4.5 billion years, and with routine precisions in the 0.1 1 percent range. [Parrish, Randall R.; Noble,… … Wikipedia
Lead-lead dating — is a method for dating geological samples, normally based on whole rock samples of material such as granite. For most dating requirements it has been superseded by uranium lead dating (U Pb dating), but in certain specialized situations (such as… … Wikipedia
dating — I In geology and archaeology, the process of determining an object s or event s place within a chronological scheme. Scientists may use either relative dating, in which items are sequenced on the basis of stratigraphic clues (see stratigraphy) or … Universalium
uranium — /yoo ray nee euhm/, n. Chem. a white, lustrous, radioactive, metallic element, occurring in pitchblende, and having compounds that are used in photography and in coloring glass. The 235 isotope is used in atomic and hydrogen bombs and as a fuel… … Universalium
lead — lead1 /leed/, v., led, leading, n., adj. v.t. 1. to go before or with to show the way; conduct or escort: to lead a group on a cross country hike. 2. to conduct by holding and guiding: to lead a horse by a rope. 3. to influence or induce; cause:… … Universalium
Thorium — (pronEng|ˈθɔːriəm) is a chemical element with the symbol Th and atomic number 90. As a naturally occurring, slightly radioactive metal, it has been considered as an alternative nuclear fuel to uranium.CharacteristicsWhen pure, thorium is a… … Wikipedia
Principal cosmogenic and uranium-thorium series radioisotopes — ▪ Table Principal cosmogenic and uranium thorium series radioisotopes radioisotope half life in years principal uses Cosmogenic isotope beryllium 10 1.5(106) dating marine sediment, manganese nodules, glacial ice, quartz in rock exposures,… … Universalium
Uranium — (pronEng|jʊˈreɪniəm) is a silvery gray metallic chemical element in the actinide series of the periodic table that has the symbol U and atomic number 92. It has 92 protons and 92 electrons, 6 of them valence electrons. It can have between 141 and … Wikipedia
Uranium-uranium dating — is a radiometric dating technique utilizing the comparison of two isotopes of uranium (U) in a sample: 234U and 238U. 234U/238U dating is one of several radiometric dating techniques exploiting the uranium radioactive decay series, in which 238U… … Wikipedia
