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Chapter 3 Water and the Fitness of the Environment Lecture Outline Overview: The Molecule That Supports All of Life Because water is the substance that makes life possible on Earth, astronomers hope to find evidence of water on newly discovered planets orbiting distant stars. Life on Earth began in water and evolved there for 3 billion years before colonizing the land. Even terrestrial organisms are tied to water. Most cells are surrounded by water. Cells are about 70?95% water. Water is a reactant in many of the chemical reactions of life. Water is the only common substance that exists in the natural world in all three physical states of matter: solid ice, liquid water, and water vapor. Concept 3.1 The polarity of water molecules results in hydrogen bonding