Era
Eocene
9
20th century
8
Cretaceous
7
21st century
4
Devonian
4
Paleocene
4
Permian
4
Quaternary
4
1941-
3
Pennsylvanian
3
Tertiary
3
To 1500
3
1809-1882
2
1914-1989
2
19th century
2
Carboniferous
2
Cenozoic
2
Miocene
2
Mississippian
2
Oligocene
2
1791-1868
1
1822-1884
1
1858-1919
1
1908-1987
1
1908-1993
1
1935-
1
1940-2021
1
1948-
1
1962-
1
1981-2001
1
Holocene
1
Mesozoic
1
Paleozoic
1
Pleistocene
1
active 16th century
1