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Relatively thin life-supporting stratum of the earth's surface, extending from a few miles into the atmosphere to the deep-sea vents of the oceans. The biosphere is a global ecosystem that can be broken down into regional or local ecosystems, or biomes. Organisms in the biosphere are classified into trophic levels (seefood chain) and communities.
This entry comes from Encyclopædia Britannica Concise. For the full entry on biosphere, visit Britannica.com.