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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