Which of the following best defines the biosphere?

The biosphere is best defined as the area on Earth where all life exists because it encompasses all living organisms, their interactions, and the environments in which they inhabit. This includes land, water, and the atmosphere, extending from the depths of the oceans to the highest mountains. It integrates ecosystems and the various ecological processes that sustain life. The biosphere is crucial because it represents the sum of all ecosystems, highlighting the interconnectedness of life and the environmental conditions that support it.

Other options pertain to more specific aspects of Earth's systems. For example, one choice focuses solely on a specific part of the Earth's crust related to water, which does not encompass all life. Another describes a particular depth in the ocean that overlooks the vast array of habitats and organisms residing in shallower or terrestrial areas. The final option emphasizes species interaction within a community, which is a vital aspect of ecological studies but does not define the broader concept of the biosphere, which includes all life forms and interactions on the planet as a whole.