Water the Most Substance on Earth
Water is the most common substance on Earth, covering more than 70% of the planet’s surface. All living things consist mostly of water; for example, the human body is about two-thirds water. Earth, air, fire, and water were considered by the ancient philosopher to be the four chemical elements, a concept that persisted through the middle Ages. It was not until 1781 that Henry Cavendish showed that water was obtained by the combustion of hydrogen. Shortly afterward the discovery was made that water could be electrolytically decomposed into two volume of hydrogen and one volume of oxygen, but the chemical formula of water was a matter of controversy until 1860, when Stanislao Cannzzaro established it as H2O.