The Earth's Shifting Crust by Charles Hapgood - wire of information

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EARTH'S SHIFTING CRUST
much evidence, but it was ignored. When the Swedish scien*
tist Gerard de Geer established by clay varve counting that
the ice sheet was withdrawing from Sweden as recently as
13,000 years ago, the implications were not really accepted,
nor were his results popularly known. Books continued to appear,
even thirty years afterwards, with the original estimates
of the age of the icecap.
Then, following World War II, nuclear physics made pos-
sible the development of new techniques for dating geolog-
ical events. One of these was radiocarbon dating.
The method of radiocarbon dating was developed by
Willard F. Libby, nuclear physicist of the University of Chi-
cago, now a member of the United States Atomic Energy
Commission. It uses an isotope of carbon (Carbon 14) which
has a "half-life" of about 5,568 years (115:75). A "half-life"
is the period during which a radioactive substance loses half
its mass by radiation. Among the very numerous artificial
radioactive elements created in nuclear explosions some have
half-lives of millionths of seconds; others, occurring
in na-
ture, have half-lives of millions of years. For geological dating
it is necessary to have radioactive elements that diminish significantly
during the periods that have to be studied, and
that occur in nature.
Since radiocarbon exists in nature, and has a relatively
short half-life, the quantity of it in any substance containing
organic carbon will decline perceptibly in periods of a few
centuries. By finding out how much carbon was contained
originally in the specimen and then measuring what still re-
mains, the date can be found to within a small margin of
error.
When this method was first developed by Libby, it could
date anything containing carbon of organic origin back to
about 20,000 years ago.
Since then the method has been im-
proved, through the efforts of many scientists, and its range
has been nearly doubled.
The first major result of the radiocarbon method was the