The chemical make-up of earth's atmosphere during the cretaceous period

There are indications that the cretaceous atmosphere may have been much richer in oxygen. Today, Earth's atmosphere contains about 77% nitrogen, 21% oxygen, 1% water vapor, 0.9% argon, and 0.03% carbon dioxide, with traces of about a dozen other gases.

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answer;

d. are made mostly of liquid

explanation;

-the general   composition and structure planets includes; they have a thick gas and liquid layer covering a small,solid core. mostly the gases are hydrogen and helium atmosphere and layers of liquid hydrogen. for instance neptune and uranus are examples of the outer planets, they have a core covered by ice and ammonia.

-neptune's atmosphere is hydrogen and helium with a bit of methane so there is no oxygen to breath and the interior is made up of frozen water and ammonia with a rock and iron core. thus, there is no liquid water or solid surface to survive.