Lecture10

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10.1 How does convection work?

• Convection is the simultaneous transfer of matter and heat, whereas conduction transfers only heat from hot to cold regions.
• Convection occurs when gravity forces that cause motion are greater than the viscous forces that resist motion, otherwise heat transfers by conduction.
• The gravity force driving thermal convection originates from density contrasts between hot and cold materials. Higher density contrast is found in materials with low heat conduction and high thermal expansion.
• Calculations show that convection should occur in the whole mantle or outer core, but not the crust or inner core.
• The density differences driving outer core convection arise from compositional, rather than temperature, differences as in mantle convection.