Era
Permian
27
Precambrian
16
Ordovician
14
Cenozoic
13
Proterozoic
11
Jurassic
6
Miocene
6
Paleozoic
6
Pleistocene
6
Cretaceous
5
Mississippian
5
Quaternary
5
19th century
4
20th century
4
Pennsylvanian
4
Pliocene
4
Silurian
4
Triassic
4
21st century
3
Cambrian
3
1948-
2
Carboniferous
2
-1864
1
1851-1930
1
1858-1919
1
1865-1946
1
1876-1946
1
1952-
1
1961-
1
1995
1
Eocene
1
Mesozoic
1
Tertiary
1