Early theories about life

Some of the earliest theories of life were materialist, holding that all that exists is matter, and that all life is merely a complex form or arrangement of matter. Empedocles (430 B.C.) argued that every thing in the universe is made up of a combination of four eternal 'elements' or 'roots of all': earth, water, air, and fire. All change is explained by the arrangement and rearrangement of these four elements. The various forms of life are caused by an appropriate mixture of elements. For example, growth in plants is explained by the natural downward movement of earth and the natural upward movement of fire.