A world with high carbon content, with a crust of graphite, a mantle of diamond and at most a core of rock or metal. Any atmosphere would be reducing with carbon monoxide and hydrocarbons, but probably contain nitrogen and carbon dioxide as well. Depending on temperature, different hydrocarbons may be liquid. Some may even have two-layered oceans with an upper layer of gasoline and a lower layer of liquid water! The liquidity ranges would be further out from the star than the same liquidity ranges for Earth-like worlds due to the much stronger greenhouse effect. One idea is that life may produce and store oxygen to react with reducing atmospheric gases, but storing oxygen would be difficult due to its toxicity. The possibility of a safe store cannot be ruled out however.
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