1. The mantle is solid except for some shallow (<100 km depth) regions where small percentages of partial melting may take place.
2. Mantle rocks deform like a fluid over long time scales with viscosity ∼10 21 Pa·s by the movement of vacancies or dislocations through the crystal lattice.
3. G. Schubert D. L. Turcotte P. Olson Mantle Convection in the Earth and Planets (Cambridge Univ. Press New York in press).
4. Convective velocities are on the order of centimeters per year so one “transit” across the mantle takes ∼100 million years and one “overturn” takes ∼400 to 500 million years. Surface heat flux is 80 mW/m 2 and the cooling rate is ∼100 K per million years.
5. Strength of the lithosphere: Constraints imposed by laboratory experiments