The Past 1 Billion Years
Years
(millions)		 Life World
1000
PRECAMBRIAN
 NOT SHOWN:

HADEAN AGE
(4.5 to 3.8 billion years ago)

ARCHAEAN AGE
(3.8 to 2.5 billion years ago)

PROTEROZOIC AGE
   Paleoproterozoic Era
   (2.5 to 1.6 billion years ago)
   Mesoproterozoic Era
   (1.6 to 0.9 billion years ago)
900
800
700
600 O2 concentration reaches 1% of total atmosphere, allowing algae to survive in shallow water. Increased exposure to sunlight raises metabolic capacity, increasing further generation of oxygen.
CAMBRIAN
Explosion of algae and marine life (including many now-extinct phyla).
  
PALEOZOIC ERA
500
ORDOVICIAN
First vertebrates (Agnatha or jawless fishes).
SILURIAN
First life adapted to live on land.
 O2 concentration of about 10%, permitting plant life to survive on land.
DEVONIAN
First seed plants. AGE OF FISHES. First amphibians and insects.
400
CARBONIFEROUS
Great coal forests of ferns and trees. AGE OF AMPHIBIANS. First reptiles. Massive expansion of insects.
300
PERMIAN
AGE OF REPTILES. Decline of amphibians, last of trilobites. Decline of primitive plants.
TRIASSIC
First mammals, first dinosaurs; great cone tree forests.
  
MESOZOIC ERA
JURASSIC
AGE OF DINOSAURS. Pine tree forests; last of seed ferns.
200
CRETACEOUS
Last of dinosaurs. Massive expansion of insects, flowering plants and flowering trees.
100
 
CENOZOIC ERA
EOCENE
PRESENT


© 1997 Handprint