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• n  the watery layer of the earth's surface; includes water vapor

• Geologists see the world as a series of layers: the metallic barysphere at the center, the rocky lithosphere, the water hydrosphere, the atmosphere.
• The earth is one organism, comprising atmosphere (air), hydrosphere (water), lithosphere (rocks), biosphere (life).

Quotes

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• Svante Arrhenius in San Francisco Chronicle
  But as Arrhenius said of the report from Watson and Harrison: "A fascinating aspect of the early hydrosphere is of course the prospect of the emergence of life as soon as the watery medium makes this possible."