Benefits of Living on Earth

Abstract

Earth-life is the singular known example of life in the universe. Vast numbers of planets have and are quickly being discovered, most with properties that exclude the possibility of life as we know it. Yet, Earth is marvelously suited for life. In the search for life beyond Earth, especially sentient life, it is clear by now that most so-called habitable zone planets cannot harbor complex life. This is because of a harsh host planet, host star, and/or host galaxy environment. Earth-like planets are rare, but how rare? And what do we mean by an Earth-like planet? Even with a nearly ideal star, the Solar System gives us a large number of examples of uninhabitable worlds. How common are wet rocky planets in the Galaxy? These are some of the open questions of astrobiology. Here we enumerate some astrophysical factors or circumstances that favor the development of complex (multicellular) life on the surface of Earth. Some of these may be essential for complex life and others may be only beneficial, especially in crossing the threshold from simple to complex forms. The emergence of simple life, its transformation to complex life, and then to advanced species like animals, took many steps and a very long time. Life, if bound to its home world, is ultimately doomed. True success can be regarded as the development of life capable of intelligence based planetary protection and the ability to colonize space and other worlds. This threshold may be rarely crossed. Some of the factors listed here may be merely coincidental. Most likely, a combi- nation of many of these beneficial factors, working together, is required to provide the long term life-promoting conditions that we enjoy on Earth.