Final answer:
The correct answer is D) Atmosphere, which is the layer of gases surrounding Earth, critical for maintaining life-sustaining conditions.
Step-by-step explanation:
The subsystem composed of a mixture of gases that surrounds the Earth is the atmosphere. This gaseous layer includes nitrogen (78.1%), oxygen (21.0%), and minor elements (1%) such as argon, helium, carbon dioxide, and water vapor. The atmosphere is critical for life on Earth as it provides the necessary conditions for survival, including breathable air and a climate system that regulates temperature.
The atmosphere is distinct from other Earth subsystems such as the lithosphere, which is the outermost layer of Earth's crust, the hydrosphere, which includes all areas containing water, and the biosphere, which encapsulates all regions of Earth where life exists. Earth's atmosphere extends over three hundred miles above the surface and includes several layers: the troposphere, stratosphere, mesosphere, thermosphere, and exosphere.
The correct answer to the question is D) Atmosphere.