Biology's greatest mystery is how life began on earth three million years ago. Many cultures believed life was the work of powerful deities.  Scientists have long been seeking biological explanations for the origin of life. Aristotle's spontaneous generation theory was accepted until the 19th century. Detailed graphics, diagrams and video images tell us about Louis Pasteur's discovered of the origin of microorganisms, biogenesis, new discoveries about metabolism, the process of metabolism, definitions of life, anabolic reactions, catabolism, the Krebs cycle, enzymes, experimental metabolism without enzymes, redefining life, and ongoing research into early metabolism.