The hydrosphere is one of the four spheres of the Earth system; the other three are the geosphere or lithosphere (solid rocky part of Earth), atmosphere (gases surrounding Earth), and biosphere (living things).
The hydrosphere consists of all of the water on, in and surrounding Earth. The water in the hydrosphere is distributed among the ocean, glaciers and ice caps, groundwater, surface water and water in the atmosphere in the form of water vapour and clouds. The water is present in all three phases: solid, liquid and gas. Life on Earth depends on the water of the hydrosphere.
Earth is known as the water planet for good reason. More than 71% of Earth’s surface is covered with water. Only a small fraction of the total amount of water on Earth is available for drinking, washing and irrigating crops because most of it is either salty or frozen.
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The global ocean, along with seas and bays, accounts for 97% of all the water on Earth. Ocean water is salty and is not suitable for drinking or other everyday uses. Only 3% of the water on Earth is fresh (not salty). Over two-thirds of the fresh water is in the form of ice, in glaciers, polar ice caps or permafrost. Another 30% of the fresh water is groundwater. This leaves less than 1% of the fresh water, or 0.007% of the total water on Earth, on the surface in lakes and rivers that are easily accessible.
The hydrologic cycle, also known as the water cycle, describes how all the water in the hydrosphere continually moves between oceans, lakes, rivers, land and atmosphere. During the course of the water cycle, water changes state from liquid to gas and back to liquid. The energy that drives the hydrologic cycle comes from the sun. The steps in the water cycle are evaporation, condensation, precipitation, and run-off. Transpiration is an additional element in the water cycle.
- Evaporation is the process by which water on the surface changes from a liquid to a gas state, water vapour. Energy is required for evaporation to take place.
- Condensation occurs when water vapour in the atmosphere cools and collects into water droplets, forming clouds. The water loses energy when it condenses.
- Precipitation consists of rain, hail, sleet or snow falling from clouds back to Earth’s surface.
- Run-off is water from precipitation that flows over the surface into rivers or streams, eventually returning to the ocean.
- Transpiration happens when water vapour returns to the air from the leaves of plants.
Water that does not run-off soaks into the ground and fills the spaces between the soil and rock, becoming groundwater. This water may sometimes be accessed by wells.
The hydrosphere is the total amount of water on a planet. The hydrosphere includes water that is on the surface of the planet, underground, and in the air. A planet’s hydrosphere can be liquid, vapour, or ice.
On Earth, liquid water exists on the surface in the form of oceans, lakes and rivers. It also exists below ground—as groundwater, in wells and aquifers. Water vapour is most visible as clouds and fog.
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The frozen part of Earth’s hydrosphere is made of ice: glaciers, ice caps and icebergs. The frozen part of the hydrosphere has its own name, the cryosphere.
Water moves through the hydrosphere in a cycle. Water collects in clouds then fall to Earth in the form of rain or snow. This water collects in rivers, lakes, and oceans. Then it evaporates into the atmosphere to start the cycle all over again. This is called the water cycle.
The hydrosphere provides an important place for many animals and plants to live. Many gases nutrients e.g. nitrate, nitrite and ammonium ions, as well as other ions, are dissolved in water. The presence of these substances is critical for life to exist in water.