Wikipedia absolute dating
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.
Although zircon (Zr Si O) is most commonly used, other minerals such as monazite (see: monazite geochronology), titanite, and baddeleyite can also be used.
During the alpha decay steps, the zircon crystal experiences radiation damage, associated with each alpha decay.
In relative dating the exact age of the object is not known; the only thing which made clear using this is that which of the two artifacts is older.In radiometric dating, the radioactive minerals within the rocks are used to know about the age of the object or the sites.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.As a result, newly-formed zircon deposits will contain no lead, meaning that any lead found in the mineral is radiogenic.
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In other words, we can say that in relative dating the archaeologist determines that which of the two fossil or the artifacts are older.