The Earth’s Hydrosphere

The Earth’s hydrosphere is the water of the Earth; this is the oceans, lakes, all other surface water, the groundwater, water vapour in the air, and glaciers. It includes the liquid, solid, and gas forms of water (H2O). 97.5% of the Earth’s water is salt water, with 96.5% in the oceans and 1% as saline lakes and groundwater. Only 2.5% of the Earth’s water is freshwater, with a large part of it as glaciers (these we are losing to rising temperatures, which will effect the salinity of the oceans), snow and ice. The balance is in ground water, lakes, rivers, wetlands, soil moisture, biological water (water in plants and animals), and in the atmosphere. 2.5% is not much if you consider most life on Earth depends on fresh water for survival. Throw in the fact that we are polluting much of our water; it doesn’t leave much left over for drinking water. Water is a precious resource; one that needs to be protected for all species that depend on it.

Source: The U.S. Geological Survey’s (USGS) Water Science School – The Water Cycle

The hydrosphere is in constant movement, which is called the hydrologic cycle or water cycle. It is one of Earth’s ecoservices systems that cleans water. It is estimated that the sun’s solar energy evaporates about 320,000 cubic kilometres of water from the oceans and about 60,000 cubic kilometres of water from on land sources (like lakes and rivers). Of the 380,000 cubic km, about 284,000 will fall back into the oceans, and 96,000 will fall on land. Approximately, 60,000 cubic km of the water that falls on land will evaporate, leaving about 36,000 cubic km of water left to infiltrate the ground to reemerge as surface water later, and the water that can’t be absorb by the ground will flow over the land eroding it on its journey back to the oceans.

Reference: Earth – An Introduction to Physical Geology, 4th Canadian Ed. by Tarbuck, Lutgens, Tsujita, Hicock

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