KNOPF URANIUM AND THE AGE OF THE EARTH
AS CONVINCING NUMBERS of man's early ancestors began to emerge from their long obscurity, another question came more forcefully to the forefront than ever before. How old is man?
The point has always aroused man's curiosity. Just as someone whose birth records have been lost may have a sense of uncertainty about his place in the world, so does man feel unsure because he cannot date his own beginnings. The urge to know is deep.
More than this, the question of how old we humans are is a crucial one to the whole theory of evolution and to many related branches of science. Has there been time for the infinitely slow changes that Darwin assumed were the basis of evolution? Or, put the other way round, if man has been in existence for a shorter time, could he have changed as much as the fossil records show he has? The questions are basic, and in the end the theory of evolution must stand or fall by the answers to them. Either evolution is possible in the time that has passed, or it is impossible.
But the problem of how old man is and of the time available for his evolution is one that so far has never been directly answerable.
Recorded dates begin a mere four thousand or five thousand years ago. One of the first reliable ones is that of the eclipse of the sun that occurred in 2238 B.C., immediately before the capture and destruction of Ur by the Elamites. Beyond that earliest written moment in time, scientists until recently have