GEOLEX Help Information
Geologic Age Definitions
Relative Geologic Time GEOLOGIC
TIME
millions
of years ago

TIME OF APPEARANCE OF
DIFFERENT FORMS OF LIFE
ERA PERIOD EPOCH
C
E
N
O
Z
O
I
C
 Quaternary Holocene 1.6 ____
Pleistocene Ice age, human evolution
Tertiary Pliocene 5 Age of Mammals
Miocene 24 Spread of anthropoid apes
Oligocene 38 Origin of more modern families of mammals, grazing animals
Eocene 55 Origin of many modern families of mammals, giant mammals
Paleocene 66 Origin of most orders of mammals, early horses
M
E
S
O
Z
O
I
C		 Cretaceous Late
Early		 138 Appearance of flowering plants; extinction of dinosaurs at end; appearance of a few modern orders and families of mammals
Jurassic Late
Middle
Early		 205 Appearance of some modern genera of conifers; origin of mammals and birds; height of dinosaur evolution
Triassic Late
Middle
Early		 240 Dominance of mammal-like reptiles
P
A
L
E
O
Z
O
I
C		 Permian Late
Early		 290 Appearance of modern insect orders
Carboniferous Pennsylvanian Late
Middle
Early		 320 Dominance of amphibians and of primitive tropical forests which formed coal; earliest reptiles
Mississippian Late
Early		 360 Earliest amphibians
Devonian Late
Middle
Early		 410 Earliest seed plants; rise of bony fishes
Silurian Late
Early		 435 Earliest land plants
Ordovician Late
Middle
Early		 500 Earliest known vertebrates
Cambrian Late
Middle
Early		 570 Appearance of most invertebrate phyla
P
R
E
C
A
M
B
R
I
A
N		 Proterozoic Late
Neoproterozoic		 3,800 Origin of life; algae; worm burrows
Middle
Mesoproterozoic
Early
Paleoproterozoic
Archean

Table derived from: California Geology, Fig.1, p.93, July/August 1996.
Precambrian divisions derived from: The Museum of Paleontology (University of California at Berkeley) web site: http://www.ucmp.berkeley.edu/precambrian/precambrian.html