Rubidium strontium dating range
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The main point is that the ages of rock formations are rarely based on a single, isolated age measurement.
By the late 18th century, some naturalists had begun to look closely at the ancient rocks of the Earth.There are a number of long-lived radioactive isotopes used in radiometric dating, and a variety of ways they are used to determine the ages of rocks, minerals, and organic materials.Some of the isotopic parents, end-product daughters, and half-lives involved are listed in Table 1.The point is that not all methods are applicable to all rocks of all ages.One of the primary functions of the dating specialist (sometimes called a geochronologist) is to select the applicable method for the particular problem to be solved, and to design the experiment in such a way that there will be checks on the reliability of the results.It is based on the radioactivity of Ar, however, is an inert gas that escapes easily from rocks when they are heated but is trapped within the crystal structures of many minerals after a rock cools. This correction can be made very accurately and has no appreciable effect on the calculated age unless the atmospheric argon is a very large proportion of the total argon in the analysis.
The geochronologist takes this factor into account when assigning experimental errors to the calculated ages. First, there must be no argon other than that of atmospheric composition trapped in the rock or mineral when it forms.
The K-Ar clock works primarily on igneous rocks, i.e., those that form from a rock liquid (such as lava and granite) and have simple post-formation histories.
It does not work well on sedimentary rocks because these rocks are composed of debris from older rocks.
For example, a method based on a parent isotope with a very long half-life, such as C method can only be used to determine the ages of certain types of young organic material and is useless on old granites.
Some methods work only on closed systems, whereas others work on open systems.
The discovery of radioactivity in 1896 by Henri Becquerel, the isolation of radium by Marie Curie shortly thereafter, the discovery of the radioactive decay laws in 1902 by Ernest Rutherford and Frederick Soddy, the discovery of isotopes in 1910 by Soddy, and the development of the quantitative mass spectrograph in 1914 by J. Thomson all formed the foundation of modern isotopic dating methods.