_Speak to the earth, and it shall teach thee._ —JOB 12:8 Our Part of the Geologic Time Scale The dead hand of another system of classification lies across a still larger area than the Stone Age itself or the Age of Man. This area is the entire life of our earth since it took sufficient shape to support cellular life. As it is so large an area and much of it is so remote in time, changes in the definition of most of its various divisions do not much affect the present discussion. Once upon a time there were four great divisions, neatly numbered in Latin as the Primary, the Secondary, the Tertiary, and the Quaternary. The first two went by the board when newer scientists found older ages and stretched the life of the earth a couple of billion years. The Tertiary is still a respected appellation, but the good name of the Quaternary—the area of time with which this book is mainly concerned—is seriously questioned. Defined as the Age of Man, it was supposed to harbor all evidence of his existence; but hints of his presence in the Tertiary have rather sullied the scientific standing of the later period. [Illustration: THE LIFE STORY OF THE EARTH _This summary of the story of the earth is a combination of charts in Arthur Holmes’_ Principles of Physical Geology, _Earnest A. Hooton’s_ Up from the Ape, _and George Gaylord Simpson’s_ The Meaning of Evolution, _with modifications by William C. Putnam and James Gilluly. *The divisions marked with an asterisk used to be called, respectively, Secondary and Primary._] PALEONTOLOGICAL DIVISIONS GEOLOGICAL DURATION IN CUMULATIVE DIVISIONS YEARS TOTALS (_Round numbers_)