Lead isotope dating

Radioactivity was discovered in 1896 by French physicist Henri Becquerel.By 1907 study of the decay products of uranium (lead and intermediate radioactive elements that decay to lead) demonstrated to B. Boltwood that the lead/uranium ratio in uranium minerals increased with geologic age and might provide a geological dating tool.The two cascades are different—235U becomes 207Pb and 238U becomes 206Pb.What makes this fact useful is that they occur at different rates, as expressed in their half-lives (the time it takes for half the atoms to decay). Président-Kennedy, PK-7150, Montréal, QC, H2X 3Y7, Canada Received 23 March 2009; Revised 2 December 2009; Accepted 24 January 2010Academic Editor: Artemi Cerda Copyright © 2010 Diane Saint-Laurent et al.This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited., polycyclic aromatic hydrocarbons (PAHs), and other contaminants (e.g., As, Cd, Cu, Pb) were recently discovered on the banks of the Saint-François and Massawippi rivers.Uranium comes in two common isotopes with atomic weights of 235 and 238 (we'll call them 235U and 238U).Both are unstable and radioactive, shedding nuclear particles in a cascade that doesn't stop until they become lead (Pb).

The atmosphere is recognized as major means of transport [8], but fluvial transport also constitutes a vector of pollution [9–11].The atomic masses of the different Pb isotopes are too similar and their chemical properties are identical.Unless YECs want to invoke groundless miracles or other speculations, the only known way of varying the 206Pb/204Pb and 207Pb/204Pb ratios in different rocks and minerals is through the radiometric decay of uranium OVER TIME.The 235U–207Pb cascade has a half-life of 704 million years and the 238U–206Pb cascade is considerably slower, with a half-life of 4.47 billion years.So when a mineral grain forms (specifically, when it first cools below its trapping temperature), it effectively sets the uranium-lead "clock" to zero. Its crust is continually being created, modified, and destroyed.As a result, rocks that record its earliest history have not been found and probably no longer exist. 101-102; 1991, chapter 7) strongly argues for a 4.5 billion year old Earth on the basis of lead (Pb) isotopes in meteorites, lunar samples and Earth rocks. 101) admits that many terrestrial lead samples do not EXACTLY lie on a 4.55 billion year old meteorite isochron. 24) fails to mention that these deviations are trivial (also see Figure 8 in Dalrymple, 1984, p. Specifically, the uncertainty in the age of the Earth as derived from Pb isotope measurements is only about 2% (Dalrymple, 1984, p. When compared with meteorites, Earth rocks generally have much more complex histories, which may include weathering from oxygen and water, melting, metamorphism (heating without melting), faulting or other alteration events.Of course, young-Earth creationists (YECs) reject these results because Pb-isotope dating clearly refutes their antiquated biblical beliefs. To be exact, the Earth is so dynamic that few terrestrial samples older than 3.8 billion years have been found (for some details, see Dalrymple, 1991, chapter 4). 117), nature cannot fractionate (that is, separate and concentrate) 204Pb, 206Pb, 207Pb, and other lead isotopes from each other.However, Dalrymple (1991, chapter 7) discusses both the successes (e.g., Tera, 1981) and failures (e.g., the faulty assumptions in Ulrych, 1967) in interpreting the geochronology of terrestrial leads.Despite Woodmorappe's (1999) misunderstandings about the Precambrian history of the Earth and the functioning of geological processes, Pb-isotope dating of meteorites, lunar samples and terrestrial rocks, as well as the great complexity and destructive processes on the Earth's surface are entirely consistent with the Earth being 4.5 billion years old (Dalrymple, 1991, chapter 7).

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