Arizona Through Time
Origins of Life
Life originated on earth nearly 4 billion years ago, yet multicellular life,
organisms composed of more than one, differentiated cells, did not appear
for over 3 billion years. Thus most of the history of life on this earth is
little known.
Journey onto Land
The emergence of vertebrates onto land, and the transition from fish to
amphibian is well known. Less appreciated is the emergence onto land of
plants and at least eleven other animal groups.
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