Introduction To Radiometric Dating 2
General Mechanism Of Radiometric Dating 2
Problems Associated With Radiometric Dating 3
Radiometric Dating Methods 4
Uranium-Lead (U-Pb) Method 4
Potassium-Argon (K-Ar) Dating Method 5
Radioactive Carbon (C14) Dating Method 5
Rubidium-Strontium (Rb-Sr) Dating Method 5
Samarium-Neodymium (Sm-Nd) Dating Method 6
Rhenium-Osmium (Re-Os) Dating Method 6
The Shrimp Technique Of Dating 6
Fission Track Dating Method 7
Thermoluminescence (Tl) Dating Method 7
Electron Spin Resonance (Esr) Dating Method 7
Applications Of Radiometric Dating 8
Radiometric Dating – Calculating the Age of Rocks and Minerals
Introduction to Radiometric Dating
Earth has undergone drastic changes during the past 4.6 billion years and the study of the chronology of these events has been a major challenge for geologists. As these changes take place at a gradual pace when compared to the human life span, geologists have to rely on various chronometric dating methods to date these changes on the geological time scale. Relative dating methods like geological dating provide a relative date that is calculated based on the information about various geological events obtained from the rock’s record. In contrast, radiometric dating provides a more accurate numerical age for fossils and earth materials. Radiometric dating is among the most recent and commonly used chronometric dating methods which calculates a numerical age of the rock’s formation.
Radiometric dating is based on the radioactive decay of a large number of radio-isotopes present in the earth’s crust. Out of the several naturally occurring isotopes, some exist in the form of stable isotopes which do not change with time, and some exist in the form of radio-isotopes or unstable isotopes that have a tendency to convert into other elements spontaneously. The process of spontaneous conversion into other elements is also known as radioactive decay. The rate of decay of the radio-isotopes provides a natural clock, helping in the assessment of the age of the sample in which the rate of decay remains unaffected by other geological processes. Radiometric dating compliments geological dating and helps in the geo-chronological studies. Geological dating through a stratigraphic correlation method is commonly used to calculate the age of the sedimentary and volcanic rocks that lie exposed on the Earth's surface. Although, this method cannot be applied to igneous and metamorphic rocks. Radiometric dating helps in the assessment of the age of igneous and metamorphic rocks (Mussett and Khan, 2000) (Peppe and Deino, 2013).
The primary objective of this paper aims to describe various radiometric dating methods and the changes in the radiogenic isotopes accounted for, under these methods. This paper also provides information about specific types of radiometric applications, and in addition outlines some problems associated with the science of radiometric dating.
General Mechanism of Radiometric Dating
Electrons, protons and neutrons are the fundamental components of atoms in all elements. The isotopes of an element have the same atomic number (depending on the number of protons) but different mass numbers (depending on the total number of protons and neutrons). For instance, U238 and U235 are two isotopes of uranium that have the same atomic number 92, however they have different weight percentages, mass numbers and completely different half lives. The radioactivity associated with U235 is 2.2% and with U238 is 48.9% in which both decay gradually to a stable condition. The original isotope is known as the parent and the resultant elements, obtained from the decay process, are known as the daughter elements. Table 1 given on page 5, shows various radioactive parent isotopes and their respective stable daughter products. The rate of decay is the fraction of the radioactive element decaying in a unit time and is symbolized as λ