| http://www.w3.org/ns/prov#value | - ier gases and gaseous compounds, such as carbon dioxide, nitrogen, oxygen, ozone, and argon terrestrial planets ??? ??? ??? planets that are composed mostly of hydrogen and helium gas giant ??? ??? ??? What is Venus mostly composed of? carbon dioxide, with some amounts of nitrogen, helium, neon, argon ??? ??? ??? What is Mars' atmosphere composed of? a thin layer of carbon dioxide, with nitrogen,
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