SUMMARY

This contribution provides a necessarily brief summary of radioactive dating techniques which can produce dates ( ages ) ranging from tens to thousands through millions to billions of years often with assumptions not universally accepted, especially those involving the assessments of half-lives and radioactive decay constants.

1. INTRODUCTION

Radioactive dating methods involve use of radioactive isotopes of various elements. Of the more than 1500 presently known nuclides, over four-fifths are unstable although most do not occur naturally on Earth, because of their very rapid rates of radioactive decay. To date rocks and minerals, naturally occurring radioisotopes are used that continued to exist long after the so-called Big Bang because of their extremely slow rates of radioactive decay. These include uranium-238, uranium-235, thorium-232, rubidium-87 and potassium-40. Some result from the radioactive decay of long-lived, naturally occurring radioactive parents and among these are uranium-234, thorium-230 and radium-226. Others may have been created by natural nuclear reactions and these include radiocarbon (carbon-14) and tritium (hydrogen-3). Today artificial radionuclides have been introduced into the environment as a result of thermonuclear testing and the operation of nuclear fission reactors and particle accelerators.

Whatever its sources, radioactivity is significant as regards geochronology and radioactive dating began in an attempt to determine the age of the Earth once the phenomenon was discovered and uranium and thorium minerals were found to emit radiation. Two new elements were identified, namely polonium and radium, and the word radioactivity ...