Abstract
IN the determination of the geological ages of minerals by radioactivity methods, much attention is being given to those ages which are of the greatest antiquity. There are several reasons for this. The age of the oldest mineral sets a minimum value for the age of the earth; also a probable minimum age is set for the solar system and extra-terrestrial matter in general. A bottom ‘rung’ is given for any stratigraphical age column, and these great ages are of value when attempting to draw up possible maximum life-spans for the evolution of living organisms to their present state of complexity. In areas of extreme antiquity, suitable minerals may be used for the indirect determination of the decay constants of potassium1; furthermore, areas of greatest age are the most suitable places for seeking possible undetected radioactivities (for example, indium-115 2). Consequently, it is highly desirable that these greatest ages be known accurately and that several checks be made.
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