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Posted by / 25-Feb-2020 20:21

Uranium thorium dating method

These types of minerals often produce lower precision ages than igneous and metamorphic minerals traditionally used for age dating, but are more common in the geologic record.

During the alpha decay steps, the zircon crystal experiences radiation damage, associated with each alpha decay.

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).

Undamaged zircon retains the lead generated by radioactive decay of uranium and thorium up to very high temperatures (about 900 °C), though accumulated radiation damage within zones of very high uranium can lower this temperature substantially.

This effect is referred to as discordance and is demonstrated in Figure 1.and most refined of the radiometric dating schemes.It can be used to date rocks that formed and crystallised from about 1 million years to over 4.5 billion years ago with routine precisions in the 0.1–1 percent range. This mineral incorporates uranium and thorium atoms into its crystal structure, but strongly rejects lead when forming.However, use of a single decay scheme (usually Pb) leads to the U–Pb isochron dating method, analogous to the rubidium–strontium dating method.Finally, ages can also be determined from the U–Pb system by analysis of Pb isotope ratios alone. Clair Cameron Patterson, an American geochemist who pioneered studies of uranium–lead radiometric dating methods, used it to obtain one of the earliest estimates of the age of the Earth.

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If a series of zircon samples has lost different amounts of lead, the samples generate a discordant line.

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