Light is so common that we often take it for granted. Yet without it, our world would be nothing but a cold, dark, lifeless matter. Light from the sun makes the earth warm enough for life. It also makes green plants grow. Plants are food for animals. Plants also give off oxygen that you breathe in the air. Dead plants provide fuel that we use for energy. Plants that died millions of years ago turned into coal and oil that people now use to make the heat and electricity.