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Many radioactive to stable isotope decay series, each with a unique decay constant, can be used, often together, to determine robust formation ages for Earth materials, especially for older materials. ssss1 summarizes some common examples. Three of these are discussed in more detail in the sections that follow.

Uranium (U) occurs in two radioactive isotopes, both of which decay in steps to different stable isotopes of lead (Pb). The closely related actinide element thorium (Th) decays in a similar fashion to yet another stable isotope of lead. The essential information on the radioactive and stable isotopes involved for these three decay series (²³⁸U →²⁰⁶Pb,²³⁵U →²⁰⁷Pb, and²³²Th → ²⁰⁸Pb) is summarized in ssss1. This includes the types of decay processes, their half‐lives, and the useful age range for dating by each of these methods.

Of the three decay series, the most commonly used is²³⁸U → ²⁰⁶Pb. This is because²³⁸U is much more abundant than the other two radioactive isotopes and thus it and its daughter product are easier to measure accurately. Typically, heavy minerals, such as zircon, sphene, and/or monazite, are used for analyses because they contain substantial actinides, are relatively easy to separate and resist chemical alteration.