K
tL
1
-
1
+
1
--.~-(z2-Z1)
C
1
IC
=
P.C
4z.
It
=
0.4.
The
specific heat of the
volume
=
0.5.
R
is the radius of the earth in
cm
n
=
3.1415.
The
calculation yields
1000
million years.
The
depth gradient [inverse of the "geothermal gradient"] is
usually considered to
be a
constant
number
which is independent of the
nature of the rock.
(By
depth gradient
we
understand the vertical
distance between
two
layers
whose
temperature difference is
10
Celsius.) This distance is usually taken to
be
30
m.
This cannot
be
correct.
The
depth gradient depends
on
the internal conductivity of
the rock.
surface
rock boundary
[Fig.]
We
must have
W1
=
W2,
since experience
shows
that at
a
given depth the temperature
is stationary, i.e., heat accumulation does not take place. Hence:
4z =
____
1
3
- I
-C
IC.
IC,
or
If one assumes that t1 - t2
=
t3 - t4
=
10, then
h1/h2
=
k1/k2.
The
depth gradients are proportional to the coefficients of thermal
conductivity of the rocks.
Diurnal and annual fluctuations of temperature
near the surface of the earth.
If
one
monitors the temperature at the surface of the earth
on
a
normal day throughout
24
hours,
one
can see that the variation of the
temperature can
be
approximately represented
by
the formula
t
=
a0
+
a1
sin(2_.
z}.
40