Book contents
- Frontmatter
- Contents
- Preface and Philosophy
- Abbreviations and acronyms
- Part I Planetary perspective
- Part II Earth: the dynamic planet
- Chapter 4 The outer shells of Earth
- Chapter 5 The eclogite engine
- Chapter 6 The shape of the Earth
- Chapter 7 Convection and complexity
- Part III Radial and lateral structure
- Part IV Sampling the Earth
- Part V Mineral physics
- Part VI Origin and evolution of the layers and blobs
- Part VII Energetics
- References and notes
- Appendix
- Index
Chapter 6 - The shape of the Earth
Published online by Cambridge University Press: 05 June 2012
- Frontmatter
- Contents
- Preface and Philosophy
- Abbreviations and acronyms
- Part I Planetary perspective
- Part II Earth: the dynamic planet
- Chapter 4 The outer shells of Earth
- Chapter 5 The eclogite engine
- Chapter 6 The shape of the Earth
- Chapter 7 Convection and complexity
- Part III Radial and lateral structure
- Part IV Sampling the Earth
- Part V Mineral physics
- Part VI Origin and evolution of the layers and blobs
- Part VII Energetics
- References and notes
- Appendix
- Index
Summary
When Galileo let his balls run down an inclined plane with a gravity which he had chosen himself … then a light dawned upon all natural philosophers.
I. KantTerrestrial planets are almost spherical because of gravity and the weakness of rock in large masses. The largest departures from sphericity are due to rotation and variations in buoyancy of the surface and interior shells. Otherwise, the overall shape of the Earth and its heat flow are manifestations of convection in the interior and conductive cooling of the outer layers. The style of convection is uncertain. There are various hypotheses in this field that parallel those in petrology and geochemistry. The end-members are whole-mantle convection in a chemically uniform mantle, layered convection with interchange and overturns, and irreversible chemical stratification with little or no interchange of material between layers. Layered schemes have several variants involving a primitive lower mantle or a depleted (in U and Th) lower mantle. In a convecting Earth we lose all of our reference systems. The mantle is heated from within, cooled from above and experiences secular cooling. Global topography and gravity provide constraints on mantle dynamics.
Topography
Although the Earth is not flat or egg-shaped, as previously believed at various times, neither is it precisely a sphere or even an ellipsoid of revolution. Although mountains, ocean basins and variations in crustal thickness contribute to the observed irregular shape and gravity field of the Earth, they cannot explain the long-wavelength departures from a hydrostatic figure.
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- Chapter
- Information
- New Theory of the Earth , pp. 62 - 72Publisher: Cambridge University PressPrint publication year: 2007