Geological time

The geologic time scale (GTS) is a system of chronological dating that relates geological strata (stratigraphy) to time. 

It is used by geologists, paleontologists, and other Earth scientists to describe the timing and relationships of events that have occurred during Earth's history. 

The primary defined divisions of time are eons, in sequence 

  • the Hadean (4130 - 4600 million years ago)
  •  the Archean (2800 -4000 million years ago)
  •  the Proterozoic and the Phanerozoic (~635-2500 million years ago)

The first three of these can be referred to collectively as the Precambrian supereon. 

Eons are divided into eras, which are in turn divided into periods, epochs and ages.

Super Eons: ( there is essentially only 2 Precambrian and everything else)

  • -
  • Precambrian
    • the Hadean


  • Phanerozoic
  • Proterozoic
  • Archean
  • Hadean


  • Cenozoic
  • Mesozoic
  • Paleozoic
  • Neoproterozoic
  • Mesoproterozoic
  • Paleoproterozoic
  • Neoarchean
  • Mesoarchean
  • Paleoarchean
  • Eoarchean
  • Early Imbrian (Neohadean)
  • Nectarian (Mesohadean)
  • Basin Groups (Paleohadean) 
  • Cryptic (Eohadean) 4,680 to 4,630 Ma

Periods (Ma - Millions of yers ago)

  • Quaternary
  • Neogene
  • Paleogene
  • Cretaceous
  • Jurassic
  • Triassic
  • Permian
  • Carboniferous (303.7-323.2)
  • Devonian (419.2-372.2)
  • Silurian (423 - 443.8)
  • Ordovician (485.4  - 445.2 )
  • Cambrian (541-489.5 )
  • Ediacaran (~635 )
  • Cryogenian (~720 Ma)


These are subdivisions of periods often with specific names or designated early, middle or late. Recent epochs include Holocene, Pleistocene


These are again another subdivisions, but of the Epochs above. The most recent age is called the Meghalayan.  Ages are more often known in subdivisions for more early times for example  Late Cretaceous Maastrichtian.


It’s pretty hard to mentally recall the 100s of millions of years ago and what ages they are. Why is there no ‘metric system' for these time periods? like why not just start with years then? well you can like this… 

1 million years ago what was this time period ? - it was the Quaternary period mostly

2 million years ago what was this age? also part of the Quaternary

5 million years ago now this is getting into the Neogene period

10 million years ago still in the Neogene period, sigh

20 million years ago on the way to Paleogene

30 million years ago definitely in the Paleogene

40 million years ago still in the Paleogene

50-60 million years ago that’s it for the Paleogene

60-70 million years ago it’s the Cretaceous 

70-80 mya it’s still the Cretaceous 

80-90 cretaceous they call it late Cretaceous 

90- 145 mya the early Cretaceous 

145-160 mya  it’s the Jurassic! 

and so on… 

Source adapted from: Wikipedia contributors. (2020, January 7). Geologic time scale. In Wikipedia, The Free Encyclopedia. Retrieved 03:56, January 13, 2020, from