Geology Reference
In-Depth Information
Table B.1.
Parameters of heat-producing isotopes.
Decay const.
a
,
λ
i
(Ga
−
1
)
Power
a
(μW/
kg element)
Element/U
b
(g/g)
Power,
h
i
(μW/kg U)
Isotope,
i
Half-life (Ga)
238
U
4.468
0.155
94.35
1
94.35
235
U
0.7038
0.985
4.05
1
4.05
232
Th
14.01
0.049
26.6
3.8
101.1
40
K
10
4
1.250
0.554
0.0035
1.3
×
45.5
Total
245
a
Stacey [141].
b
Galer
et al.
[242].
Table B.2.
Parameters of the thermal evolution model of Figure 9.1
(except for parameters related to crystallisation of the inner core).
Quantity
Symbol
Value
Inputs
:
Urey ratio
Ur
0.69
Plate adjustment factor
0.16
Plume adjustment factor
0.12
1300
◦
C
Reference mantle temperature
T
r
10
21
Pa s
Reference mantle viscosity
μ
r
E
∗
Viscous activation energy
325 kJ/mol
3500
◦
C
Initial temperature, upper mantle
T
U
4500
◦
C
Initial temperature, lower mantle
T
L
6070
◦
C
Crystallisation temperature (centre)
Outputs
:
Final temperature, upper mantle
1306
◦
C
T
U
2306
◦
C
Final temperature, lower mantle
T
L
3876
◦
C
Final temperature, outer core
T
C
Final surface heat loss
Q
S
36.4 TW
Final core heat loss
Q
C
7.6 TW
Final radiogenic heating
Q
R
24.6 TW
Maximum thermal dissipation
1.23 TW
Final thermal dissipation
0.41 TW
Final total dissipation
1.82 TW
Such a high starting temperature for the core gains some rationale from recent
suggestions that the core might be superheated. The idea is that a large amount of heating
occurs as core material separates from the mantle (enough to heat the whole Earth by
around 2000
◦
C), but that most of the heating occurs in the core material. The core
material might have to collect into large bodies before it can sink through the relatively
cool and stiff mantle, in which case it probably would not thermally equilibrate with the
