Earth, Our Environment - Class Notes
Chapter 2, Earth: Origin and Composition - 08
Some basic facts about heat:
- Heat always flows from hot to cold.
- Heat is transfered by two processes: Conduction and Convection.
- The Earth is hotter than space so heat flows out of Earth.
[ Study Figure 2.25 on page 40 of the text ]
Conduction is a slow way to transfer heat and dominates in Earth's lithosphere because the rocks there are too cool to flow quickly enough to transfer heat.
Convection is an efficient way to cool off by forming currents of hot and cold material. Earth's outer core and mantle are two separate convecting systems.
Plate Tectonics is a Consequence of Convection
- Plate tectonics is the surface manifestation of convection.
- Hot material is brought up from the mantle and frozen to make new ocean floor. Over the time of about 200 million years, this ocean cools by transmitting heat to the ocean and then the atmosphere.
- Old, cool ocean floor is then recycled back into Earth, to make room for the warmer material.
Another method of heat transmission in Earth is the formation of plumes. The exact nature of plumes is unknown, some believe they arise from the core-mantle boundary, others favor a shallower source.
[Study Figure 2.26 on page 41]
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