1630s, atmosphaera (modern form from 1670s), from Modern Latin atmosphaera, from atmo-, comb. form of Greek atmos "vapor, steam" + spharia "sphere" (see sphere). Greek atmos is from PIE *awet-mo-, from root *wet- "to blow, inspire, spiritually arouse" (see wood (adj.)). First used in English in connection with the Moon, which, as it turns out, doesn't have one.
Figurative sense of "surrounding influence, mental or moral environment" is c.1800.