noun, plural: biospheres
(1) The part of the earth where living things exist.
(2) The part of the earth (or planet) that is capable of supporting life.
(3) The living things and their environment.
(4) All of the ecosystems of the earth.
There are also artificial biospheres that have been made mainly for research and investigation, such as the Biosphere 2, which is by far the largest closed ecology system ever built by mankind.