Technically, given that the planets in this system are all named for Roman gods, we should be Terrans (from Terra, Roman earth goddess, rough equivalent of the Greek Gaia). However, when bad sci-fi movies were being made in the Fifties, nobody thought it would be worth bothering with doing any research, so they developed the diminutive "Earthlings", intended to evoke "fledglings" in the listener's mind.
I prefer "Terran", of course. (As James White pointed out in his Sector General stories, every species' name for itself would most likely translate as "human", and they would think of all others as "nonhuman" - yes, even the elephantine Tralthans, and the insectile Cinrusskin.)
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Sodium is a metal that reacts explosively when exposed to water. Chlorine is a gas that'll kill you dead in moments. Together they make my fries taste good.