Era
20th century
8,859
19th century
4,199
21st century
1,958
18th century
1,311
1945-
810
Civil War, 1861-1865
785
17th century
778
1564-1616
720
Cretaceous
704
1945-1989
664
16th century
496
1933-1945
472
1989-
468
Revolution, 1775-1783
424
To 1500
423
1946-
421
Tertiary
411
2009-
392
2001-2009
367
Early modern, 1500-1700
336
Quaternary
329
1991-
325
Colonial period, ca. 1600-1775
319
Precambrian
313
Paleozoic
299
1960-
268
Cenozoic
268
2000-
249
1951-
247
Permian
236
1993-2001
217
Eocene
216
1809-1865
205
1918-1945
205
Mesozoic
199
Miocene
199
1949-
194
Jurassic
194
1981-2001
190
Pennsylvanian
189
Pleistocene
186
1947-
184
1948-
175
Ordovician
173
Devonian
166
1979-
162
Mississippian
159
1608-1674
155
1950-
154
1980-
154
more ...