Radiometric age dating

Radiometric age dating is a powerful chronological tool. It is based on the accumulation of the daughter nuclide produced by the decay of the parent isotope. If the decay rate is known, and if one can measure the amounts of parent element and daughter isotope, then it is... 

Radiometric age dating indicates that in many regions, the lithospheric mantle formed at about... 

Were all of these newly discovered substances also new elements This question would not be answered for some years but there was a flurry of other major discoveries to keep the protagonists occupied. Pierre Curie discovered that radioactivity released large quantities of heat (Curie and Laborde 1903) which appeared mysterious—as if the heat was coming from nowhere. This discovery provided an extra heat source for the Earth and reconciled the estimates of a very old Earth, based on geological estimates, with the young age calculated by Lord Kelvin from cooling rates. The year 1903 also witnessed the first demonstration that a-decay released He (Ramsay and Soddy 1903). The build up of He was soon put to use to date geological materials, initially by Rutherford in 1905 who calculated the first ever radiometric age of 500 Myr for a pitchblende sample, and then by Strutt who examined a wide variety of minerals (Strutt... 

Young R. A. (1977) The lunar impact flux, radiometric age correlation, and dating of specific lunar features. Proc. 8th Lunar Sci. Conf, 3457-3474. 

As with most foram records, the atmospheric record cannot be dated with radiometric techniques. Dating of the record has been accomplished by correlation with the orbitally tuned deep-sea record (Sowers et al., 1993), using estimates of ice accumulation rates, ice flow models, and estimates of offsets between snowfall and gas closure ages (Petit et al., 1999), and by direct orbital tuning of the atmospheric oxygen record itself (Shackleton, 2000). Separate tuning of the marine and atmospheric records establishes independent chronologies for the two. 

One can apply the formalism discussed above to a wide variety of systems to produce a radiometric date. In this book, we will use the word date to mean the time calculated from the ratio of a radioactive isotope and its daughter isotope using the equation for radioactive decay. An age is the time between a natural event and the present. A date becomes a valid age when the conditions described in the previous paragraph are met. This terminology, suggested by Faure (1986), is not always used in the literature, where age and date are often used interchangeably. But there is value to the distinction because it helps a reader understand which numbers are significant. 

As with all radiometric dating systems, the K- Ar system will only produce a valid age if the basic assumptions of radiometric dating are satisfied. In particular, a valid age can only be obtained if the samples remained closed to diffusion of argon either into or out of the system. Two different approaches can be taken to date an object with the 40K-40Ar system. 

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