Teach Astronomy - Cosmic Context for Life

http://www.teachastronomy.com/ Cosmology sets the context for the discussion of life in the universe. Our current view of the universe is that it is large, old, and cold. The universe is expanding from an initial hot, dense state, about eleven or twelve billion years ago, the big bang. The universe therefore is several times older than the Earth itself, and so life had billions of years to evolve and develop before the Earth even formed. The universe is huge and filled with matter in the form of stars and galaxies. The total number of galaxies is about fifty or sixty billion. Together they contain ten to the power twenty stars, a hundred billion billion stars, and this forms the total set of potential sites for life. So the universe has plenty of potential places that life could exist and has had plenty of time to evolve the complex chemical and biological processes needed for life.