Era
Cenozoic
20
Precambrian
20
Proterozoic
19
Cretaceous
15
Tertiary
14
Paleozoic
11
Cambrian
9
Pennsylvanian
9
Eocene
8
Jurassic
8
Mesozoic
8
Miocene
6
Permian
6
Quaternary
6
Ordovician
5
Neogene
4
Archaean
3
Mississippian
3
Pleistocene
3
Silurian
3
Devonian
2
1885-1951
1
1890-1980
1
1940-
1
1971
1
Holocene
1
Oligocene
1
Paleogene
1
Triassic
1