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

THE MOUNTAINS 117
of the earth. Smart, for example, is of the opinion that radio-
activity cannot produce heat in the earth as fast as it can be
radiated through the crust into outer space (396:62).
Some of the essential facts in any consideration of the
question of the origin of the earth's heat may be summarized
as follows. First, we know nothing of the temperature of
the earth's interior. We can only guess at it. We have made
deductions concerning it from the heat gradient observed
in the world's deepest mines. As we descend to a depth of
about four miles, the heat steadily increases (194:139). We
have assumed that the increase of heat continues at the same
rate farther down, perhaps all the way to the earth's center,
but there are a number of facts that throw doubt on this
assumption. For one thing, Daly thought
he saw evidence
that the heat gradient differs in America and in Europe,
being somewhat steeper in North America (194:139). This
would imply that there is more heat in the earth's crust in
North America than there is in Europe. Benfield produced
much more evidence of variations in heat from place to
place (28) which are difficult to reconcile with a uniform heat
gradient in the earth.
Geophysicists have now concluded that the earth's heat
originates in the crust itself, and does not come from the
deep interior (194:157). The considerations on which this
conclusion is based are too technical for discussion here, but
there seems to be no reason to doubt their validity. This con-
clusion is, of course, irreconcilable with any assumption that
the earth's heat is simply the remnant of far higher tempera-
tures prevailing in a molten stage.
A matter of great importance for the general problem is
the rate at which heat migrates through the crust, and is
dissipated into outer space. Geophysicists
have determined
that the rate of heat migration through the crust is extremely
slow. Jeffreys calculated that it would take 130,000,000 years
to cool a column of sedimentary rock 7 miles below the
earth's surface by 250 C. (241:136). As a result of this,
the climate of the earth's surface is determined entirely by the