This is an image of the ocean floor of the Earth, showing mountain ranges, subduction trenches, tectonic plates, and mid-ocean ridges.
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Image from: U.S. Geological Survey

Cooling History, part 1

A planetary body, whether the body is a planet or a moon, cools slowly by radiating energy away into space. The warmth remaining inside a body controls what sort of surface activity, atmospheric activity, and interior activity which the body has. As planetary bodies cool slowly, heat diminishes, and the activities diminish to nothing. Examination of a body for various kinds of activities tells scientists what stage a body is in it's history of cooling.

The heat of a body comes from

  • 1.) leftover heat from it's formation
  • 2.) radioactive material found in the body
  • 3.) outside forces on the body as a whole, such as those which cause tides
  • 4.) heat brought to the atmosphere by energetic particles in space
  • 5.) warming by the sun
The terrestrial planets have internal heat due to (2) above, and this source of energy drives continental drift on the surface. The giant planets have internal heat due to (1) above, and this source of energy drives the motions of the atmosphere.

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