What is the term for a part of the world in which life can exist?

The correct answer is the biosphere, which refers to the global sum of all ecosystems and indicates the regions of the Earth where life exists. This includes various habitats such as forests, oceans, grasslands, and polar regions, encompassing all living organisms and their interactions with the environment.

The geosphere pertains to the solid Earth and its geological components, including rocks and soils, rather than the living aspects of the planet. The hydrosphere encompasses all the water bodies on Earth, including oceans, rivers, lakes, and moisture in the atmosphere, but does not specifically denote the living organisms within those environments. The atmosphere consists of the gases surrounding the Earth, necessary for life but not inclusive of the life forms themselves. Hence, the biosphere is the most accurate term for defining the regions of the Earth capable of supporting life.