Isostasy

Isostasy - 1 Plate Tectonics I: Isostasy 1. Fluids flow...

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1 c:\work\classes\ess1\isostasy.doc Plate Tectonics I: Isostasy 1. Fluids flow until their surfaces are level and the higher-density fluid is below the lower-density one. 2. Most of the Earth is hot enough to be fluid/viscous (on geologic timescales), so the Earth is also arranged this way, with densities in the order: core > mantle > crust > ocean > atmosphere. 3. Only the top 1-60 kilometers of the Earth are cold and stiff enough to resist horizontal flow; this layer is called the lithosphere . 4. Even the lithosphere bends and rises or sinks until isostasy = the condition of equal mass in all vertical columns. 5. Continents float higher than ocean-floor because their crust is 30-75 km thick, versus 5-10 km under oceans. 6. After a disturbance (like an Ice Age), isostasy needs about 5,000 years to be re-established, due to the viscosity of the asthenosphere .
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2 c:\work\classes\ess1\isostasy.doc PLATE TECTONICS I: ISOSTASY Plate tectonics is the convective style of our planet. Continents occasionally split and drift apart, leaving new oceans between. This is happening now in the Red Sea-Gulf of Aqaba between Africa and Arabia. The Atlantic also formed when North and South America separated from Eurasia and Africa. (This was the first example of "continental drift" to be discovered.) Drift is only possible because there is a "fluid", not a "solid" foundation for the plates. Today we will discuss the Earth as a collection of fluids, which may suprise you. Actually, this view of the Earth only dates back to the 1950's. This "paradigm shift" made plate tectonics conceivable!
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This note was uploaded on 10/14/2010 for the course ESS ESS1 taught by Professor Bird during the Spring '10 term at UCLA.

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Isostasy - 1 Plate Tectonics I: Isostasy 1. Fluids flow...

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