Era
Cretaceous
21
Tertiary
15
Jurassic
13
Quaternary
13
Mesozoic
8
Mississippian
7
Paleozoic
7
21st century
6
Permian
5
Triassic
5
20th century
4
Carboniferous
4
Miocene
4
Pennsylvanian
4
Silurian
4
Devonian
3
Oligocene
3
Pleistocene
3
Cenozoic
2
Pliocene
2
1779-1843
1
Cambrian
1
Eocene
1
Neogene
1
Ordovician
1
Precambrian
1