206Pb

206Pb is a stable isotope of the element lead (Pb), with 82 protons and 124 neutrons. Like other lead isotopes, it is identified by the mass number 206. In nature, lead consists of several isotopes, including 204Pb, 206Pb, 207Pb, and 208Pb, with 206Pb making up roughly a quarter of natural lead.

206Pb is the radiogenic end product of the uranium-238 decay series. It is produced over geologic time as U-238 decays through a long chain of intermediates to 206Pb. The decay of uranium-238 has a long characteristic timescale, with a half-life of about 4.468 billion years, so 206Pb accumulates in rocks and minerals as uranium gradually decays. Because 206Pb is stable, its quantity remains once formed.

The ratios of 206Pb to other uranium-related isotopes are central to uranium-lead dating (U-Pb dating). By measuring 206Pb/238U and 206Pb/207Pb in a material, scientists can determine the time elapsed since the mineral crystallized, making U-Pb dating a primary method for dating ancient geological materials. This approach has been crucial in dating Earth’s oldest rocks and meteorites, contributing to estimates of the age of the Solar System at about 4.56 billion years.

In addition to its dating role, 206Pb is one of the four stable lead isotopes (204Pb, 206Pb, 207Pb, 208Pb). Lead remains toxic to health and the environment, but isotope studies focus on interpreting isotope ratios rather than chemical differences among the isotopes.