207Pb206Pb

207Pb206Pb refers to a lead isotope pair. Lead-207 (207Pb) and Lead-206 (206Pb) are both stable isotopes of the element lead. Lead is a chemical element with the symbol Pb and atomic number 82. Natural lead is composed of four stable isotopes: 204Pb, 206Pb, 207Pb, and 208Pb.

206Pb is the most abundant stable isotope of lead, making up approximately 24.1% of natural lead. It is a decay product of uranium-238 (238U) through a series of alpha and beta decays, with 238U having a half-life of about 4.468 billion years. This decay chain makes 206Pb particularly important in radiometric dating, specifically uranium-lead dating and its variations like concordia-discordia dating. By measuring the ratio of 206Pb to 238U, scientists can determine the age of rocks and minerals.

207Pb is the second least abundant stable isotope of lead, comprising about 22.1% of natural lead. It is a decay product of uranium-235 (235U) through its own decay chain, which has a half-life of about 703.8 million years. Similar to 206Pb, the 207Pb/235U ratio is also used in radiometric dating. The combined measurement of 206Pb/238U and 207Pb/235U ratios provides a powerful tool for geochronology, allowing for more robust age determinations.

The existence and abundance of these lead isotopes are fundamental to understanding geological timescales and the history of radioactive elements on Earth. Their presence in geological samples serves as a chronological marker, allowing scientists to reconstruct past events.