PowerPoint Presentation
Heat flow, thermal regime, energy budget of the
EarthDefinitionsMeasuring heat flowKelvin and the age of the
EarthRadioactivityContinental heat flow (1)Oceanic heat flow
(1)Global budget (1)Continental vs oceanic heat flowPlate model for
the oceansContinental heat flow (2)Global budget (2)Constraints on
the temperature regimeThermodynamics1st law: heat is a form of
energy dU = dQ -PdV Q = C T 2nd law (simple form): heat goes from
hot to cold (Entropy can only increase unless work is done. Work
can be extracted from system only if there are a cold and a hot
source). Conduction of heat (Fourier): q = -k grad T Other
mechanisms of heat transport (radiation, convection).
Some numbersk (thermal conductivity) 3 W/m/K (average for most
rocks)Temperature gradient 20-30 K/km Heat flow If gradient does
not decrease with depth, temperature at 100km >2000K and
temperature at CMB > 60,000K
Kelvin and the age of the Earth
Radioactivity
Oceanic heat flow
Surprise !!!Continental crust is radioactive and thickOceanic
crust is thin with almost no heat generationOceanic heat flow <
Continental heat flow ?NO difference?
Energy Budget of the earth (1)Birch (1951)Total flux = 30 TWHeat
production in chondrites = 5 pW/kgMass of earth = 6 1024
kgCoincidence?
Thermal model for continents