I'm pretty sure your answer would be the atmosphere. Geosphere, Atmosphere, Hydrosphere and Biosphere are the four major spheres of the Earth. If you want to know more to prove my answer, then Cryosphere.
Geosphere: The land mass of the Earth, the rock and the core. It takes up the most of the Earth's space.
Hydrosphere: The bodies of water found on the planet. Oceans, streams, lakes, etc..
Atmosphere: Earth's air and gases make up the atmosphere.
Biosphere: The plants and animals, basically all life that makes up Earth.
Cryosphere: The naturally occurring ice, also called water storage of the Earth. Glaciers are an example of part of the cryosphere.
