"How does convection work?"
What will be an ideal response?
Answer: "Convection is the simultaneous movement (transfer) of matter and heat, whereas conduction transfers only heat from hot to cold regions. Convection happens when gravity forces that cause motion are greater than viscosity forces that resist motion; in other circumstances, heat transfers by conduction. Thermal convection originates from density contrasts between got and cold materials. Higher density contrast, which favors convection, is present in materials that have low heat conductivity and large expansion when heated. Calculations show that convection should occur in the whole mantle and in the outer core, but not within the lithosphere or inner core. Convection in the outer core results from density variations caused by compositional differences, rather than by temperature differences that cause mantle convection."
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