Geologic time: clock analogy.
<P>
   This clock scales Earth's history of 4.6 billion years to one hour.
<P>
   Humans  appeared  about  one  second  ago  when  the  earliest hominin
   appeared within the last 6 to 7 million years.
<P>
   The  Phanerozoic  eon  of  over  500  million  years occupies about 11
   minutes on this clock.