Exploratour - Evolution of the Solar System
There are four ideas for the origin of a planetary atmosphere. Those four ideas are 1. that the planet-elements of which a planet was made decomposed and released the atmosphere, 2. that the atmosphere was drawn to the planet from the gaseous cloud out of which everything came, 3. that comets hit the planet and brought molecules of air with them, 4. that volcanoes erupted and made an atmosphere from gases inside the planet.
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Different of these theories apply to different of the planets in the solar system. It is thought that all the planets may have started with an atomsphere which condensed with it out of the solor nebula. The atmospheres of the giant planets may still be largely made of that original material. The atmospheres of the terrestrial planets have almost certainly changed since the dawn of time. In part because of the activity of the Sun early in the history of the solar system.
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