Where the Earth is concerned, humans live in the 'biosphere', together with all other living matter.
Overlapping the biosphere, are the hydrosphere, and the atmosphere, and below us , inside the Earth, is the lithosphere.
Above the atmosphere is the stratosphere, and then the ionosphere.
NB All theses 'spheres' overlap to some extent.
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Biosphere
Half of it.
The lower part of the mantle between the asthenosphere and the outer core.
The radius of a sphere is equal distance from the center of the sphere to all points within the sphere.
Sphere is one syllable: sphere.