Home > Geochronology

1 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.

2 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.

3 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 datingPotassium-argon or K-Ar dating is a method used by archaeologists to ascertain the date of ancient mineral deposits. The potassium isotope K40 decays to argon40 with a half-life of 1,300,000,000 years. As argon is a gas any traces of that element will esc and argon-argon dating . These techniques are used to date igneous and volcanic rocks. They are also used to date volcanic ashVolcanic ash is rock particles less than 0. 25 inch across ejected from a volcanic vent. The term for any material explosively thrown out from a vent is ejecta or pyroclastic debris. If liquid magma is ejected as a spray, the particles will solidify in th layers within or overlying paleoanthropologic sites.

Other radiogenic dating techniques include:

• Fission track dating
• Cosmogenic isotope dating

4 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 calendarCalendars A calendar is a system for assigning calendar dates to days. The dates may be based on the perceived motion of astronomical objects. A calendar is also a physical device (often paper) that illustrates the system (for example, a desktop calendar or sidereal time) or floating.

• DendrochronologyCheraw, South Carolina Dendrochronology or tree-ring dating is the method of scientific dating based on the analysis of tree ring patterns. This technique was invented and developed during the 20th century originally by A. Douglass, the founder of the Lab.
• Ice cores.
• Lichenometry.
• Paleomagnetic dating
• Varves.

5 References

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

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

See also:

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