The part of Earth where life exists is called the:

• A. Troposphere
• B. Cryosphere
• C. Stratosphere
• D. Biosphere

Answer: (D)

Life on Earth exists in the biosphere, the global zone where living organisms are found and interact with their environment. The biosphere includes ecosystems on land, in oceans and rivers, and even some life in the air. It depends on energy and material exchanges with the atmosphere, hydrosphere, and lithosphere. The other terms describe parts of Earth that are not defined by living systems: the troposphere is the lowest layer of the atmosphere where weather happens; the stratosphere lies above it and contains the ozone layer; the cryosphere includes all frozen water like glaciers and ice caps. Since the question asks for the region that supports life, the biosphere is the correct choice.