So much to do, so very much time.  Begin your tour through time on our planet Earth with this look at the Precambrian.  This extensive site from the Field Museum in Chicago takes you back 4.5 billion years ago to the beginning of life.  A brief overview talks about the single-celled organisms that evolved during the Precambrian.  There is an image gallery with dozens of pictures, and video interviews with scientists from the museum and the University of Chicago.  Visit this wonderful museum, and when you’ve exhausted the Precambrian, there are many more periods to explore.