Radiometric dating rock samples paiddatingsites com
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.But it was not until the late 1950s that all the pieces were in place; by then the phenomenon of radioactivity was understood, most of the naturally occurring isotopes had been identified and their abundance determined, instrumentation of the necessary sensitivity had been developed, isotopic tracers were available in the required quantities and purity, and the half-lives of the long-lived radioactive isotopes were reasonably well known.Some of the methods have internal checks, so that the data themselves provide good evidence of reliability or lack thereof.Commonly, a radiometric age is checked by other evidence, such as the relative order of rock units as observed in the field, age measurements based on other decay schemes, or ages on several samples from the same rock unit.Lord Kelvin and Clarence King calculated the length of time required for the Earth to cool from a white-hot liquid state; they eventually settled on 24 million years.
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.
The main point is that the ages of rock formations are rarely based on a single, isolated age measurement.
On the contrary, radiometric ages are verified whenever possible and practical, and are evaluated by considering other relevant data.
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.