Periods and
Systems
GEOLOGIC TIME
Eon Era Epochs and
Series
Beginning of
Interval*
Biological Forms

Phanerozoic

Cenozoic

Quaternary

Holocene

Pleistocene

0.01

1.8

 

Earliest humans

Tertiary

Pliocene

Milocene

Oligocene

Eocene

Paleocene

5

24

34

55

65

 

Earliest hominids

 

Earliest grasses

Earliest large mammals

Cretaceous-Tertiary boundary (65 million years ago):extinction of dinosaurs

Mesozoic

Cretaceous

Upper

Lower

98

144

 

Earliest flowering plants;
  dinosaurs in ascendancy

Jurassic

Triassic


208

248

Earliest birds

Earliest dinosaurs & mammals

Paleozoic

Permian

Carboniferous

Pennsylvanian

Mississippian

Devonian

Silurian

Ordovician

Cambrian


286

 

320

360

410

438

505

544

 

 

Earliest reptiles

Earliest winged insects

Earliest amphibians & bony fish

Earliest land plants & insects

Earliest corals

Earliest fish

Proterozoic

Precambrian



2500

Earliest colonial algae &
  soft-bodied invertebrates

Archean



3800

Earliest surviving microfossils
  of primitive single-celled
  organisms

Hadean



4600

No surviving fossils

*Approximate, in millions of years before the present