Summary Timeline ..........................................................................
Summary Timeline
13.7 billion years ago ...................... Origins of Universe.
380,000 years later .......................... Separation of energy and matter; cosmic
background radiation.
200 million years later .................... Appearance of ¿ rst stars.
11–12 billion years ago (bya) .......... First supernovae; appearance of
new elements.
4.6 bya ............................................. Creation of the Sun, solar system,
and Earth.
c. 3.5 bya ......................................... First life forms on Earth; single-celled
“prokaryotes”; photosynthesis.
c. 2–3 bya ........................................ Increase of oxygen in atmosphere due
to photosynthesis.
c. 1.5 bya ......................................... First complex or “eukaryotic” cells;
sexual reproduction?
c. 600 million years ago (mya) ....... Cambrian era; ¿ rst surviving fossils of
multi-celled organisms.
c. 500 mya ....................................... First vertebrates; supercontinent of
Rodinia breaking up.
c. 475 mya ....................................... First organisms on land.
c. 350 mya ....................................... First reptiles.
