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Geophysical surveys

, Volume 1, Issue 1, pp 99–119 | Cite as

Physical properties of the Earth's core

  • Frank D. Stacey
Article

Abstract

Calculations of the compression and temperature gradient of the core are facilitated by the use of the thermodynamic Grüneisen ratio, γ=3αKsC P . A pressure-dependent factor in γ is found to have the same numerical value for the core as for laboratory iron, justifying the use of a constant value for γ (1.6) in core calculations. The density of the outer core is satisfied by the assumption that it contains about 15% of light elements, particularly sulphur, whereas the inner core is probably ironnickel with very little lighter component. The presence of sulphur in the outer core reduces its liquidus at least 600° below pure iron, so that the adiabatic gradient does not intersect the liquidus, as Higgins and Kennedy have shown would occur in a pure iron core. The inner core is probably close to its melting point, 4700 K, and the adiabatic temperature gradient of the outer is calculated with this as a fixed point, giving 3380 K at the core-mantle boundary. The estimated electrical resistivity of the outer core, 3×10−6 Σm, corresponds to a thermal conductivity of 28 W·m−1·deg−1, which, with the adiabatic core gradient gives a minimum of 3.9×1012 W of heat conduction to the mantle. The only plausible source of this much heat is the radioactive decay of potassium in the core. As pointed out by Goles, Lewis, and Hall and Murthy, the presence of potassium becomes geochemically probable once sulphur is admitted as a core constituent. Thus it appears that the recognition of sulphur in the core resolves the two major difficulties which we have faced in attempting to understand the core.

Keywords

Thermal Conductivity Electrical Resistivity Inner Core Pure Iron Radioactive Decay 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

List of Symbols

a

equilibrium atomic spacing at zero pressure, also a constant

A

surface area of core

b

a constant

c

a constant

CV,CP

specific heat at constant volume, constant pressure

D

dimension of core (or core eddy)

E(r)

atomic interaction energy

E

energy due to atomic displacement from equilibrium

lattice energy of material

f1,f2

structure-dependent constants

F(P)

pressure dependent factor in Grüneisen's ratio

g

gravitational acceleration; also a constant (Equation (13))

H

latent heat of solidification

I

integral (Equation (23))

k

Boltzmann's constant

K

incompressibility (bulk modulus)

KT,KS

isothermal, adiabatic incompressibilities

N

number of atoms in a volume of material

P

pressure

dQ/dt

core to mantle heat flux

r

atomic spacing

re

equilibrium value ofr under pressure

Rm

magnetic Reynolds number

T

temperature

Tc

critical temperature

TR

reduced temperature (Equation (39))

U

specific internal energy of a material

v

velocity of internal core motion

V

volume

volume expansion coefficient

β

compressibility

γ

thermodynamic Grüneisen ratio (Equation(2))

η

magnetic diffusivity

κ

thermal conductivity

κe

electronic contribution to κ

μ0

permeability of free space

ϱ

density

ϱe

electrical resistivity

σR

reduced conductivity,ϱeM/ϱe

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Copyright information

© Reidel Publishing Company 1972

Authors and Affiliations

  • Frank D. Stacey
    • 1
  1. 1.Physics Dept.University of QueenslandBrisbaneAustralia

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