The Nature of Life

Abstract

At this time and location, about 14 billion years after the enigmatic beginning of the universe, in the outer parts of an average galaxy, in a planetary system formed 5 billion years ago around an ordinary star, we observe a special phenomenon: The surface of one of the planets is covered by a biosphere. It is a complex network of organic chemistry taking place in water solution. This chemistry is driven mostly by the energy streaming from the star, and it maintains a diversity of living beings, from unicellular microbes to large plants and animals. These form complex ecological communities, with long energy-transferring interactions (food chains), which effectively circulate carbon compounds between oxidized and reduced states. In particular, photosynthesis using sunlight by the green plants and algae converts the oxidized carbon, CO₂, into reduced carbon compounds (sugars), which are used as chemical energy by other organisms. The photosynthesis binds large amounts of carbon into organic compounds (biomass), while animal respiration and decay of organic material again release CO₂ into the air.