Era
Cretaceous
19
Quaternary
10
Cenozoic
9
Tertiary
9
Jurassic
8
Pennsylvanian
8
Mississippian
7
Ordovician
7
Permian
7
Eocene
6
Miocene
5
Triassic
5
Cambrian
4
Oligocene
4
Carboniferous
3
Paleozoic
3
Pleistocene
3
Mesozoic
2
Neogene
2
Paleocene
2
Paleogene
2
1932-1987
1
Devonian
1
Precambrian
1
Silurian
1