Sararin samaniyar duniya, wanda aka fi sani da iska, shine iskar gas ɗin da ke riƙe da ƙarfin Duniya wanda ke kewaye da duniyar kuma ya samar da yanayin ta na duniya . Yanayin Duniya yana kare rayuwa a doron ƙasa ta hanyar haifar da matsin lamba wanda ke ba da damar ruwa mai ɗorewa ya kasance a farfajiyar Duniya, yana ɗaukar hasken rana na ultraviolet, yana dumama farfajiyar ta hanyar riƙe zafi ( tasirin greenhouse ), da rage matsanancin zafin rana tsakanin dare da rana ( zafin rana. bambancin). Ta ƙarar, busasshiyar iska ta ƙunshi 78.08% nitrogen, 20.95% oxygen, 0.93% argon, 0.04% carbon dioxide, da ƙananan gas. Har ila yau, iska tana ƙunshe da adadin tururin ruwa, a matsakaita kusan kashi 1% a matakin teku, da 0.4% akan sararin samaniya. Haɗin iska, zafin jiki, da matsin yanayi suna bambanta da tsayi. A cikin yanayi, iska dace da amfani a photosynthesis da terrestrial shuke-shuke da kuma numfashi na nazarin sasannin dabbobi ke samuwa ne kawai a Duniya ta troposphere .[ana buƙatar hujja] Farkon yanayin duniya ya ƙunshi iskar gas a cikin nebula na rana, da farko hydrogen.