CARBON-14 AND THE REDATING OF THE LAST 25,000 YEARS
MANY THOUSANDS OF YEARS AGO a fine spruce forest grew in a region now known as Two Creeks, Wisconsin. It might have gone the unnoticed way of most forests if the weather had not grown colder, and if the great icecap that covered the northern top of the continent had not begun a new push to the south. The great mass of ice ground down upon the spruce forest, snapping off the trees, shoving over the stumps, and leaving them, like so many matchsticks, all pointed to the southwest, the direction of the glacier's movement.
This ancient and far from unique contest between ice and wood again might have gone forever unmarked except that the glacial advance that mowed down the Wisconsin forest was the last of our time. After this final thrust the climate grew warmer, the ice melted, and the part of the continent that is now Canada and the United States became habitable for man. By the most careful studies, scientists judged that this turning- point in history occurred about twenty-five thousand years ago.
And this verdict might have stood undisputed if a tall quiet physical chemist at the University of Chicago had not proved, in 1950, that ancient bits of organic matter, like the fossilized wood of the Two Creeks spruce trees, carry their own dates written within them.
The chemist, Dr. Willard F. Libby, reduced some few ounces of the ancient wood to pure carbon, and spread it in one