Define uranium lead dating
Join Britannica's Publishing Partner Program and our community of experts to gain a global audience for your work! This dating method is based upon the decay of radioactive potassium-40 to radioactive argon-40 in minerals and rocks; potassium-40 also decays to calcium-40.Thus, the ratio of argon-40 and potassium-40 and radiogenic calcium-40 to potassium-40 in a mineral or rock is a measure of the age of the sample.
To date past events, processes, formations, and fossil organisms, geologists employ a variety of techniques.
This then can be used to deduce the sequence of events and processes that took place or the history of that brief period of time as recorded in the rocks or soil.
For example, the presence of recycled bricks at an archaeological site indicates the sequence in which the structures were built.
Without absolute ages, investigators could only determine which fossil organisms lived at the same time and the relative order of their appearance in the correlated sedimentary rock record.
Unlike ages derived from fossils, which occur only in sedimentary rocks, absolute ages are obtained from minerals that grow as liquid rock bodies cool at or below the surface.
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In the ideal case, the geologist will discover a single rock unit with a unique collection of easily observed attributes called a marker horizon that can be found at widely spaced localities.