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Geochronology

Introduction

Geochronology is the science of determining the age of rocks, fossils, and sediments. A variety of dating methods are used by geologists to achieve this.

Dating methods

• Radiometric techniques measure the decay of radioactive isotopes, and other radiogenic activity.
• Incremental techniques measure the regular addition of material to sediments or organisms.
• Correlation of marker horizons allow age-equivalence to be established between different sites.

Radiometric dating

By measuring the rate of radiocative decay of a radioactive isotope with a known half-life, geologists can establish the absolute age of the parent material. A number of radioactive isotopes are used for this purpose, and depending on the rate of decay, are used for dating different geological periods.

• Radiocarbon dating. This technique measures the decay of Carbon-14 in organic material (e.g. plant macrofossils).
• Uranium-series dating. This technique is used to date Speleothems, Corals, carbonates, and fossil bones.
• Potassium-argon dating and argon-argon dating. These techniques are used to date igneous and volcanic rocks. They are also used to date volcanic ash layers within or overlying paleoanthropologic sites.

Other radiogenic dating techniques include:

• Fission track dating
• Cosmogenic isotope dating

Incremental dating

Incremental dating techniques allow the construction of year-by-year annual chronologies, which can be fixed (i.e. linked to the present day and thus calendar or sidereal time) or floating.

• Dendrochronology.
• Ice cores.
• Lichenometry.
• Paleomagnetic dating
• Varves.

References

Lowe, J.J., and Walker, M.J.C. (1997), Reconstructing Quaternary Environments (2nd edition). Longman publishing ISBN 0582101662

Smart, P.L., and Frances, P.D. (1991), Quaternary dating methods - a user's guide. Quternary Research Associaiton Technical Guide No.4 ISBN 0907780033

See also:

• Arthur Holmes;
• Fritz Houtermans;
• Alfred O. C. Nier.