Transcript Estructura del interior de la tierra

• 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
• 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:
(T  T )  T
z
•The rate of flow of heat per unit area up
through the plate, Q, is:
 T  T  T 
Q  k 

z


T
Q( z )  k
z
•In the limit as δz goes to
zero:
T
Q( z )  k
z
• Heat flow (or flux) Q is rate of flow of heat per unit area.
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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
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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 :
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Silver
Magnesium
Glass
Rock
Wood
420
160
1.2
1.7-3.3
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.wisconline.com/Objects/ViewObject.
aspx?ID=sce304
•Convection