February, 1931 



EVOLUTION 



Page nine 



the mineral what degree of disintegration it has undergone we 

 can get a measure of the number of years that have elapsed 

 since the mineral was first formed in its fresh state in the rocks. 



Thus measuring the age of the earth in the chemical lab- 

 oratory, we arrive at even more astonishing estimates of geo- 

 logic time than were obtained by the older methods. If, using 

 these newer methods, we hastily run the gamut of some of the 

 major events of geologic history, dating them as we go, we 

 find that the oldest rocks now exposed on the earth's surface 

 were formed something like 1500 million years ago. 



The first clearly recognizable remains of living forms pre- 

 served in the rocks — forms that lived in the sea — appeared at 

 least 600 million years ago, although less direct evidences show 

 that life itself appeared much earlier than this. 



Something like 400 million years ago living forms first 

 crawled out of the sea to inhabit the land — these first known 

 land animals being scorpions. Footprints in rocks formed 

 perhaps 350 million years ago are our first record of back- 

 boned animals living on the land at least part of the time. 



About 40 million years ago appeared the lemurs, the first rep- 

 resentatives of the great group of primates to which man be- 

 longs. And perhaps half a million years ago appeared in far 

 off Java the first of the forms that can properly be called 

 human. 



If, to grasp more readily the relative values of these in- 

 tervals of time, we should reckon as one day of 24 hours the 

 time since clearly recognizable forms of life appeared on the 

 earth, then man has existed only for the last minute of that 

 day and the entire sweep of English History since the Ancient 

 Britons first crossed the channel from the continent has occu- 

 pied only the last second of that day. 



How reliable is this geologic clock based on the dissociation of radio- 

 active elements? Can we be absolutely sure that their disintegration 

 has continued at exactly the same invariable rates throughout all the 

 vast stretches of time? Possibly not; but this at least is true, the 

 relative ages of various rocks as determined by this method agrees with 

 their relative ages as determined by their geologic relations to each 

 other — and this fact gives us confidence in the method. At least our 

 clock never strikes ten until it has struck nine and does not strike 

 nine until after it has struck eight. 



Making due allowance for all the uncertainties of such 

 methods of estimating geologic time, it is at least clear that 

 the physical conditions on the earth's surface began to be hos- 

 pitable for life at petiods almost inconceivably long ago and 



that throughout all subsequent time they have never varied 

 sufficiently to result in its extinction, for the chain of life de- 

 velopment has been continuous. There seems to be no reason 

 to expect that our physical surroundings will cease to be hos- 

 pitable to life for countless ages to come. In the relatively 

 brief space of man's existence on the earth — the last minute 

 in our geologic day — he has harnessed the inanimate forces 

 of nature and has brought all other forms of animal life except 

 a few disease germs into subjection to him; he has greatly ex- 

 tended his tetm of life by his partial conquest of disease and 

 by better protection from the elements; and he has developed 

 powers and qualities of mind and spirit not remotely ap- 

 ptoached by other living creatures. 



With a clear field ahead, what magnificant ptogress may be 

 his if he accepts his responsibility for continued progress. His 

 main enemies are now within himself — and he may well beware 

 lest in the increased ease of living he loses the vigor and the 

 homely virtues that are necessary for the progress of the race 

 upward and onward. 



Ripple-marked Potsdam sandstone with trilobite trails, Port Henry, 

 N. Y. (In New York State Museum). 



ABORIGINES of Stone Age culture 

 are reported to have been found by W. 

 Lloyd Warner, anthropologist, on small 

 islands north of Australia. He said that 

 they have no religion and no money, but 

 an elaborate social organization, marked 

 rules of conduct and obedient children. 

 They are polygamous and the women do 

 most of the wotk. Their only weapons 

 are stone-headed spears. 



BEST EVt>LlTION I'.MVIPHLi;'!' 

 The clearest, simplest explanation of 

 Evolution is "The Proofs of Evolution" 

 by Henshaw Ward, excellent for be- 

 ginners and opponents. Sent postpaid 

 for lOc; 20 for ^1. 



.^C;.\IN— OUR NEW .VDDRESS 

 344 E. 16th St., New York, N. V. 



NEW SUB.SCRIPTION R.\TES 



Single subscription, ^2 per year. Ad- 

 ditional subscriptions ^1. Five year sub- 

 scription, or a bundle of 5 copies one 

 year to one address, ^5. Foreign sub- 

 scriptions, 10c. extra. 



Quantity rates: Prepaid, 12 copies for 

 ^1. On consignment, 10c. per copy. 

 THE JOI RNAL OF HEREDITY 



Published by the American Genetic 

 Association, promotes a "knowledge of 

 the laws of heredity and their application 

 to the improvement of plants, animals, 

 and human racial stocks." Will interest 

 every serious student of Evolution. 

 Monthly, ^3.50 per year. With Evolu- 

 tion one year ^4.50. Evolution, 344 

 East 16th Street, New York. 



TO TEA( HERS OF BIOLOGY 



Many High School Science depart- 

 ments are using and recommend Evo- 

 lution. Several take over a himdred 

 copies of each issue for their students. 

 Try it this month. We'll send you 12 

 copies for ^1. 



IF YOU'VE MOVED 



Be sure to send us your old address 

 as well as your new one so that we can 

 correct our mailing list, which is arranged 

 geographically. If you hear any com- 

 plaint about non-receipt of Evolu- 

 tion, please call attention to this. 

 Many old subscribers will have moved 

 since our last issue, and we shall appre- 

 ciate your co-operation to locate them. 



