This is an image of the ocean floor of the Earth, showing mountain ranges, subduction trenches, tectonic plates, and mid-ocean ridges.
Click on image for full size
Image from: U.S. Geological Survey
A planetary body, whether the body is a planet or a moon, has to cool off. The warmth contained 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 off.
The heat of a body comes from
- 1.) leftover heat from when it formed
- 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 Earth-like planets have internal heat due to (2) above, and this source of energy causes continental drift
on the surface. The giant planets have internal heat
due to (1) above, and this source of energy causes the motions of the atmosphere.
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