Energy sources and life

Abstract

An external energy source is a necessary condition for life, because living systems require a flow of energy to organize materials and maintain a low state of entropy (Morowitz 1968). Energy is also needed to perform work. Life on Earth can be distinguished by the external energy source that it uses. Photoautotrophic life derives energy from sunlight and uses CO2 as a carbon source. Chemolithotrophic life uses redox reactions involving abiological compounds and chemolithoautotrophic life uses CO2 (or other small carbon compounds) as a carbon source. Chemoheterotrophic life uses high-energy organic molecules, produced in general by autotrophic life, as a source of energy and carbon. On other worlds, where other forms of energy may be more abundant, or where the primary sources for energy on Earth may be lacking, life may have evolved to depend on different forms of energy. In this chapter, we critically analyze the various forms of energy that are potentially available to living systems, consider other factors that bear on the evolution of energy harvesting mechanisms, and evaluate the apparent availability of different forms of energy at different sites in our Solar System. © Springer-Verlag Berlin Heidelberg 2008.