Constitucion y dinamica del planeta Conduccion del Calor.

Heat in the Earth Volcanoes, magmatic intrusions, earthquakes, mountain building and metamorphism are all controlled by the generation and transfer of heat in the Earth. The Earth’s thermal budget controls the activity of the lithosphere and asthenosphere and the development of the basic structure of the Earth.

Heat Transfer Mechanisms Conduction Transfer of heat through a material by atomic or molecular interaction within the material Radiation Direct transfer of heat as electromagnetic radiation Convection Transfer of heat by the movement of the molecules themselves Advection is a special case of convection

The heat arriving from the Sun is by far the greater of the two Heat arrives at the surface of the Earth from its interior and from the Sun. The heat arriving from the Sun is by far the greater of the two Heat from the Sun arriving at the Earth is 2x1017 W Averaged over the surface this is 4x102 W/m2 The heat from the interior is 4x1013 W and 8x10-2 W/m2 However, most of the heat from the Sun is radiated back into space. It is important because it drives the surface water cycle, rainfall, and hence erosion. The Sun and the biosphere keep the average surface temperature in the range of stability of liquid water. The heat from the interior of the Earth has governed the geological evolution of the Earth, controlling plate tectonics, igneous activity, metamorphism, the evolution of the core, and hence the Earth’s magnetic field.

Conductive Heat Flow Heat flows from hot things to cold things. The rate at which heat flows is proportional to the temperature gradient in a material Large temperature gradient – higher heat flow Small temperature gradient – lower heat flow

Imagine an infinitely wide and long solid plate with thickness δz . Temperature above is T + δT Temperature below is T Heat flowing down is proportional to: The rate of flow of heat per unit area up through the plate, Q, is: In the limit as δz goes to zero:

Heat flow (or flux) Q is rate of flow of heat per unit area. The units are watts per meter squared, W m-2 Watt is a unit of power (amount of work done per unit time) A watt is a joule per second Old heat flow units, 1 hfu = 10-6 cal cm-2 s-1 1 hfu = 4.2 x 10-2 W m-2 Typical continental surface heat flow is 40-80 mW m-2 Thermal conductivity k The units are watts per meter per degree centigrade, W m-1 °C-1 Old thermal conductivity units, cal cm-1 s-1 °C-1 0.006 cal cm-1 s-1°C-1 = 2.52 W m-1 °C-1 Typical conductivity values in W m-1 °C-1 : Silver 420 Magnesium 160 Glass 1.2 Rock 1.7-3.3 Wood 0.1

Oceanic Heat Flow Heat flow is higher over young oceanic crust Heat flow is more scattered over young oceanic crust Oceanic crust is formed by intrusion of basaltic magma from below The fresh basalt is very permeable and the heat drives water convection Ocean crust is gradually covered by impermeable sediment and water convection ceases. Ocean crust ages as it moves away from the spreading center. It cools and it contracts.

These data have been empirically modeled in two ways: d=2.5 + 0.35t2 (0-70 my) and d=6.4 – 3.2e-t/62.8 (35-200 my)

The model of plate cooling with age generally works for continental lithosphere, but is not very useful. Variations in heat flow in continents is controlled largely by changes in the distribution of heat generating elements and recent tectonic activity.

Range of Continental and Oceanic Geotherms in the crust and upper mantle

http://www.wisc-online.com/Objects/ViewObject.aspx?ID=sce304

Convection