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3.4: The Hydrosphere, Cryosphere and Biosphere

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    Hydrosphere and Cryosphere

    The hydrosphere includes all the waters on the Earth's surface, such as oceans, lakes, rivers, streams, and groundwater. 97% of all water on earth is seawater (discussed in Chapter 7).

    The cryosphere is the frozen water on Earth including glaciers, sea ice, snow, freshwater ice, and frozen ground (permafrost).

    The hydrologic cycle illustrates the movement of water through the hydrosphere and cryosphere. The movement of water and ice erodes the land surface and provides ocean basins with sediment. Dissolved materials become the salt in seawater. Salts in seawater are concentrated as water evaporates and later falls as precipitation, with most of it falling back into the ocean. The rest falls on land and becomes ice, runoff, groundwater, or is absorbed and released by living things, mostly plants.

    The Water Cycle illustrated
    Figure 3.6. The hydrologic cycle illustrates the movement of water through the hydrosphere and cryosphere.

    The Biosphere

    The term biosphere is the regions of the Earth occupied by living organisms. Life as we know it requires liquid water. So far, a biosphere is only known on Earth. Earth's biosphere encompasses the land's surface, oceans and surface waters (including the seabed in the deepest parts of the ocean basins). Life is found in the lower atmosphere (considering birds, flying insects, and wind-blown pollen and microbes), and deep underground,such in caverns, and even deeper where microbes have been found in groundwater and in porous spaces between mineral grains of solid rock deep in the subsurface. Microbes can tolerate the near boiling temperatures and extreme acidic conditions of hotsprings and thermal pools in Yellowstone National Park and other hydrothermal settings around the world. Microbes are found consuming and degrading oil reserves in petroleum reservoirs deep underground. One of the most sought goals in space exploration is to find evidence of biospheres on other planets and moons.