Planets, Exoplanets and Life ~ David Pulley

Astronomers and philosophers have been speculating that life can exist on other worlds since time immemorial but it has only been in the last few decades have we have been able to discover planets orbiting stars other than our Sun.  The search for life, even within our own solar system, remains in its infancy and so far planet Earth is the only planet that we know of that supports life.  When we search for life, can we learn anything from its evolution on planet Earth?