HOW OLD IS MOTHER EARTH Geologists Estimate It at Five Million Years. No more than five million years were required for formation of the gologic processes which are re- corded in the rocks of the earth, Professor Charles Schuchert of Yale university said in estimating the age of the earth in the third of his series of lectures on history of the world at the university Thursday night. The physicists, however, he said, are more liberal in their estimates and on the basis of the radioactiv- ity of minerals would allow twice or more than twice that amount. Time estimates are made by the gelogists, Professor Schuchert stated, in several different ways. One method is the amount and rate of accumulation of salts in the ocean. Another is the time required in the accumulation of thousands of feet of such rocks as limestones, shales and sandstones. Still other partial estimates are made from the retreat of waterfalls. The wa- terfalls, however, are temporary features and can serve only in es- timating short periods of time. The wear of the mountains and the quantity of sediments carried from them afford partial estimates. To wear down a great range of moun- tains such as the Appalachians, he stated, requires probably not less than fifteen million years. The next lecture of the series will be delivered tonight on the great reptiles of the medieval world. The lectures are given in K hall at 7:30 p. m., and are open to the public.