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The Biosphere: The biosphere is part of the earth in which life exists. It is 20 km thick from the bottom of the ocean to the lower atmosphere. It consists of three layers: the lithosphere, which is the land on the surface of the earth; the hydrosphere, which comprises of the water on the earth as well as water vapor in the air; and the atmosphere, which is made up of the air that surrounds the …

…other compounds crucial to the formation and sustenance of life. Changes in an ecosystem are brought about by different factors. For example, ecological succession brings about the replacement of one community by another in an ecosystem. In other instances, organisms that colonize an area with no community present are considered pioneer organisms. A climax community is the final stage of development of organisms and can be disrupted by a major catastrophe like a volcanic eruption.