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The Convecting Earth

We now recognize that there was a second error in Kelvin's assumptions -- heat travels from the interior of the Earth towards the surface by convection as well as conduction. There are two regions in the Earth's interior where convection is important. One is the liquid core where currents of hotter-molten metal rise and colder-molten metal sink. The second is the asthenosphere, a zone of solid, but hot, plastic rock that deforms or smushes like silly putty. The asthenosphere is a layer that usually lies between 100 and 300 km. beneath the Earth's surface. However, in areas where hot, less dense rock is rising, it comes within a few km. of the surface. This movement of convection currents in the Earth's interior not only helps to explain how the upper parts of the Earth can be relatively hotter than they would be if heat moved only by conduction, they also allow us to understand the shape of the planet's surface, where oceans and continents occur, why there are mountains, volcanoes, and great earthquakes in Japan and California but not in Philadelphia.

I.  Conduction versus convection currents 

A. Temperature, molecular motion and density

B. Density currents and buoyancy

II. Interpreting ocean floor topography

A. Mapping ocean floor topography -- sonar

B. The age of the ocean floor

C. Interpreting the ocean floor as convection cells

1. Temp / Time curve

2. Density / Time curve

3. Elevation / Age curve

D. Implications for a dynamic planet

Objectives: 1. Predict the effects of density and/or thickness on the surface elevation of a floating object.

2. Relate the surface elevation of the Earth to the thickness of the crust, to the density of the crust.

3. Describe the layered structure of the Earth. Emphasize the significance of the asthenosphere for isostatic changes at the Earth's surface.

3. Relate temperature to molecular motion. Use the relationship to a. explain the process of conduction and b. explain density changes caused by temperature change.

4. Sketch the topographic changes that occur across the Atlantic or Pacific Ocean basins.

5. Discuss the relationships between age, density, temperature and elevation of the ocean floor as one moves from the mid-ocean ridge to the abyssal plain.

6. Relate the model of seafloor spreading to convection currents in the asthenosphere.

7. Relate the model of seafloor spreading to the movement of the continents and distribution of mountains, volcanoes and earthquakes.

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