The cooling Earth: A reappraisal

Stacey F.D. (1980) The cooling Earth: A reappraisal. Physics of the Earth and Planetary Interiors, 22 2: 89-96. doi:10.1016/0031-9201(80)90049-7

Author Stacey F.D.
Title The cooling Earth: A reappraisal
Journal name Physics of the Earth and Planetary Interiors   Check publisher's open access policy
ISSN 0031-9201
Publication date 1980
Sub-type Article (original research)
DOI 10.1016/0031-9201(80)90049-7
Volume 22
Issue 2
Start page 89
End page 96
Total pages 8
Subject 1908 Geophysics
1912 Space and Planetary Science
3101 Physics and Astronomy (miscellaneous)
3103 Astronomy and Astrophysics
Abstract By treating the lithosphere as a diffusive boundary layer to mantle convection, the convective speed or mantle creep rate, ε{lunate} ̇, can be related to the mantle-derived heat flux, Q ̇. If cell size is independent of Q ̇2 then ε{lunate} ̇ ∝ Q ̇. (If cell size varies with Q ̇, then a different power law prevails, but the essential conclusions are unaffected.) Then the factthat for constant thermodynamic efficiency of mantle convection, the mechanical power dissipation is proportionalto Q ̇, gives convective stress σ ∝ Q ̇-1, i.e. the stress increases as the convection slows. This means an increasing viscosityor stiffness of the mantle which can be identified with a cooling rate in terms of a temperature-dependent creep law. If we suppose that the mantle was at or close to its melting point within 1 or 2 × 108 years of accretionof the Earth, the whole scale of cooling is fixed. The present rate of cooling is estimated to be about 4.6 × 10-8 deg y-1 for the average mantle temperature, assumed to be 2500 K, but this very slow cooling rate represents a loss ofresidual mantle heat of 7 × 1012 W, about 30% of the total mantle-derived heat flux. This conclusion requires theEarth to be deficient in radioactive heat, relative to carbonaceous chondrites. A consideration of mantle outgassing and atmospheric argon leads to the conclusion that the deficiency is due to depletion of potassium, and that the K/U ratio of the mantle is only about 2500, much less than either the crustal or carbonaceous chondritic values. Thetotal terrestrial potassium is estimated to be about 6 × 1020 kg. Acceptance of the cooling of the Earth removes the necessity for potassium in the core.
Q-Index Code C1
Q-Index Status Provisional Code
Institutional Status Unknown

Document type: Journal Article
Sub-type: Article (original research)
Collection: Scopus Import
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