Arthur E. answered • 05/11/19
National Geographic Education Coordinator
When scientists wonder whether there is life on other planets, they often ask this question: “Is there water there?" Life as we know it would be impossible without water.
Water is a tasteless, odorless, colorless compound that makes up a large proportion of all living things. It occurs everywhere in the soil, and exists in varying amounts in the air.
Living things can digest and absorb foods only when these foods are dissolved in water. Living tissue consists chiefly of water. What is water made of? It is a simple compound of two gases: hydrogen, a very light gas; and oxygen, a heavier, active gas.
When hydrogen is burned in oxygen, water is formed. But water does not resemble either of the elements which compose it. It has a set of properties all its own.
Water, like most other matter, exists in three states: a liquid state, which is the common form, a solid, called "ice”; and a gas, called "water vapor”. In which of these forms water exists depends ordinarily on the temperature.
At 0 degrees centigrade, or 32 degrees Fahrenheit, water changes from the liquid to the solid state, or freezes. At 100 degrees centigrade, or 212 degrees Fahrenheit, it changes from the liquid to the gaseous state. This change from liquid, visible water to the invisible water gas is called "evaporation.”
Thus, if a piece of ice is brought into a warm room, it starts to become liquid or melt. If the room is warm enough, the little puddle of water formed from the melting ice finally disappears. The liquid is changed into water vapor. When water is cooled, it expands just before it reaches the freezing point.
Water as it occurs in nature is never pure in the true sense. It contains dissolved mineral material, dissolved gases, and living organisms.
