How Old is the Earth Author:Patrick M. Hurley In every age man has tried to penetrate the mystery surrounding the origins and the structure of the earth. Clues have came from study of the earth's thin crust, from analysis of the moon and the planets, from earthquakes and volcanoes, but the most promising new avenue, according to Dr. Hurley, is an understanding of the earth's radioactivity. ... more »This energy seems to generate the heat, which, as it rises to the surface, lifts the continents and makes the earth's surface buckle and wrench. Radioactivity, besides, gives the modern geologist an incomparable tool. "Each grain of sand, each minute crystal in the rocks about us is a tiny clock, ticking off the years since it was formed."« less