Exploratour - Evolution of the Solar System
Atmospheres of the giant planets have definetely evolved from their formation out of the primitive solar nebula. How much they have evolved remains to be seen, however. Because of their enormous gravity, most of the original atmosphere of the planet remains in place. (The terrestrial planets lost all of the original atmosphere they were made with, because the atmosphere drifted away).
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Jupiter is made primarily of the basic materials hydrogen and helium, which is what existed in the vicinity of Jupiter when it was forming.
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