Geological Time: Principles


Geologists determine the age of events in the geological past by relative dating (establishing which event comes first, usually by superposition and crosscutting relationships) and by numerical dating (obtaining a numerical age estimate on an event, usually by radioisotopic dating of interbedded or crosscutting igneous rocks). From these dating methods, geologists have determined that the earth is 4.5 billion years old, and that most events in the geological past took place millions to hundreds of millions of years ago.

Keywords: stratigraphy; geochronology; geological timescale; biostratigraphy; radioactivity

Figure 1.

The geological timescale.


Further Reading

Ager DV (1981) The Nature of the Stratigraphical Record, 2nd edn. New York: John Wiley & Sons.

Berggren WA, Kent DV and Hardenbol J (eds) (1995) Geochronology, Time Scales, and Stratigraphic Correlation. Society of Sedimentary Geologists, SEPM Special Publication 54.

Berry WBN (1987) Growth of Prehistoric Time Scale, 2nd edn. Palo Alto, CA: Blackwell Scientific Publications.

Dalrymple GB (1991) The Age of the Earth. Palo Alto, CA: Stanford University Press.

Dott RH Jr and Prothero DR (1994) Evolution of the Earth, 5th edn. New York: McGraw‐Hill.

Eicher DL (1976) Geologic Time, 2nd edn. Englewood Cliffs, NJ: Prentice‐Hall.

Harland WB, Cox AV, Llewellyn PG et al. (1989) A Geologic Time Scale. Cambridge: Cambridge University Press.

Parrish R and Roddick JC (1985) Geochronology and Isotope Geology for the Geologist and Explorationist. Geological Society of Canada Short Course 4.

Prothero DR (1990) Interpreting the Stratigraphic Record. New York: WH Freeman.

Schoch RM (1989) Stratigraphy, Principles and Methods. New York: Van Nostrand Reinhold.

Shaw AB (1964) Time in Stratigraphy. New York: McGraw‐Hill.

York D and Farquhar RM (1972) The Earth's Age and Geochronology. Oxford: Pergamon Press.

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Prothero, Donald R(May 2001) Geological Time: Principles. In: eLS. John Wiley & Sons Ltd, Chichester. [doi: 10.1038/npg.els.0001526]