Earth’s oceans contain 97% of the planet’s water, so just 3% is fresh water, water with low concentrations of salts. Most fresh water is trapped as ice in the vast glaciers and ice sheets of Greenland.
A storage location for water such as an ocean, glacier, pond, or even the atmosphere is known as a reservoir. A water molecule may pass through a reservoir very quickly or may remain for much longer.
The amount of time
The amount of time a molecule stays in a reservoir is known as its residence time.Earth’s oceans contain 97% of the planet’s water, so just 3% is fresh water, water with low concentrations of salts.
Most fresh water is trapped as ice in the vast glaciers and ice sheets of Greenland. A storage location for water such as an ocean, glacier, pond, or even the atmosphere is known as a reservoir.
A water molecule may pass through a reservoir very quickly or may remain for much longer. The amount of time a molecule stays in a reservoir is known as its residence time.
Three States of Water
Because of the unique properties of water, water molecules can cycle through almost anywhere on Earth. The water molecule found in your glass of water today could have erupted from a volcano early in Earth history.
In the intervening billions of years, the molecule probably spent time in a glacier or far below the ground. The molecule surely was high up in the atmosphere and maybe deep in the belly of a dinosaur.
Where will that water molecule go next?
Water is the only substance on Earth that is present in all three states of matter – as a solid, liquid or gas.
Along with that, Earth is the only planet where water is present in all three states.
Because of the ranges in temperature in specific locations around the planet, all three phases may be present in a single location or in a region. The three phases are solid (ice or snow), liquid (water), and gas (water vapor).
The Water Cycle
Because Earth’s water is present in all three states, it can get into a variety of environments around the planet. The movement of water around Earth’s surface is the hydrologic (water) cycle.
The Sun, many millions of kilometers away, provides the energy that drives the water cycle. Our nearest star directly impacts the water cycle by supplying the energy needed for evaporation.
Most of Earth’s water is stored in the oceans where it can remain for hundreds or thousands of years. The oceans are discussed in detail in the chapter Earth’s Oceans.