The geological timescale is subject to fine-tuning a) as time-stratigraphic boundaries become formally fixed in sediments/rocks by international agreement, and b) as new data are obtained that bear on the age of specific boundaries. The following compilation of ages of the lower boundaries of the most commonly used intervals is drawn the International Chronostratigraphic Chart (February, 2017). See The symbol Ma refers to ages in millions of years; and ka, to ages in thousands of years. The subdivision of the Tertiary into Paleogene and Neogene periods is now widely used, particularly in marine successions. The Paleogene encompasses Paleocene, Eocene and Oligocene epochs; the Neogene includes Miocene and Pliocene epochs. The Pennsylvanian and Mississippian are normally combined as the Carboniferous Period outside the United States. The Ediacaran Period is newly defined and ratified by the international community (Knoll et al., 2004). During the excursion, we are going to see examples of geology from nearly every interval shown from the Mesoproterozoic onwards. So keep this crib handy.

Phanerozoic Eon

Cenozoic Era
      Quaternary Period        
              Holocene Epoch      0.0117 Ma (11.7 ka)    
      Pleistocene   2.58 Ma      
  Tertiary Period        
      Pliocene Epoch   5.333 Ma    
      Miocene   23.03 Ma    
      Oligocene   33.9 Ma    
      Eocene   56.0 Ma  


      Paleocene   66.0 Ma    

Mesozoic Era

  Cretaceous Period   145 Ma    
  Jurassic   201.3 Ma    
  Triassic   251.9 Ma    
Paleozoic Era
  Permian Period   298.9 Ma    
  Pennsylvanian   323.2 Ma    
  Mississippian   358.9 Ma    
  Devonian   419.2 Ma    
  Silurian   443.8 Ma    
  Ordovician   485.4 Ma    
  Cambrian   541.0 Ma    
Proterozoic Eon

Neoproterozoic Era


Ediacaran Period

  635 Ma   Condon et al. (2005), Zhang et al. (2005)
  Cryogenian   720 Ma    
  Tonian   1,000 Ma    
Mesoproterozoic Era   1,600 Ma    
Paleoproterozoic Era   2,500 Ma    

Archean Eon

  4,000 Ma    

Age of the Earth

  4,567 Ma   Amelin et al. (2002)

Periods of the Paleozoic and Mesozoic eras are further subdivided into epochs, ages and chrons on the basis of included fossils. Subdivision of the Proterozoic and Archean eons is comparatively coarse because rocks of this age are poorly fossiliferous and much less abundant in outcrop.


Amelin, Y., Krot, A.N., Hutcheon, I.D., and Ulyanov, A.A., 2002, Lead isotopic ages of chondrules and calcium-aluminum-rich inclusions: Science, v. 297, p. 1678-1683.

Condon, D., Zhu Maoyan, Bowring, S., Wang Wei, Yang Aihua, and Jin Yugan, 2005, U-Pb Ages from the Neoproterozoic Doushantuo Formation, China: Science, v. 308, p. 95-98.

International Commission on Stratigraphy, 2017, International Chronostratigraphic Chart:

Knoll, A.H., Walter, M.R., Narbonne, G.M., and Christie-Blick, N., 2004, A new period for the geologic time scale: Science, v. 305, p. 621-622.

Zhang Shihong, Jiang Ganqing, Zhang Junming, Song Biao, Kennedy, M.J., and Christie-Blick, N., 2005, U-Pb sensitive high-resolution ion microprobe ages from the Doushantuo Formation in south China: Constraints on late Neoproterozoic glaciations: Geology, v. 33, p. 473-476.