Common ancestor tree of life
This phylogenetic tree of the three domains of life (Bacteria, Archaea, and Eukarya) attempts to identify when various species diverged from a common ancestor. Finding a common ancestor for viruses has proven to be far more difficult, especially since they do not fossilize.
Source
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"OpenStax College, Organizing Life on Earth. November 9, 2013."
http://cnx.org/content/m44588/latest/#fig-ch20_01_01
OpenStax CNX
CC BY 3.0.