Isotopes used in radiometric dating
Marker horizons are stratigraphic units of the same age and of such distinctive composition and appearance, that despite their presence in different geographic sites, there is certainty about their age-equivalence.
Fossil faunal and floral assemblages, both marine and terrestrial, make for distinctive marker horizons.
Exposure dating uses the concentration of exotic nuclides (e.g.
Cl) produced by cosmic rays interacting with Earth materials as a proxy for the age at which a surface, such as an alluvial fan, was created.
The polarity timescale has been previously determined by dating of seafloor magnetic anomalies, radiometrically dating volcanic rocks within magnetostratigraphic sections, and astronomically dating magnetostratigraphic sections.
Global trends in isotope compositions, particularly Carbon 13 and strontium isotopes, can be used to correlate strata.
Two methods of paleomagnetic dating have been suggested (1) Angular method and (2) Rotation method.
By measuring the amount of radioactive decay of a radioactive isotope with a known half-life, geologists can establish the absolute age of the parent material.
Many types of luminescence techniques are utilized in geology, including optically stimulated luminescence (OSL), cathodoluminescence (CL), and thermoluminescence (TL).
Thermoluminescence and optically stimulated luminescence are used in archaeology to date 'fired' objects such as pottery or cooking stones and can be used to observe sand migration.
Tephrochronology is a method for geochemical correlation of unknown volcanic ash (tephra) to geochemically fingerprinted, dated tephra.
Tephra is also often used as a dating tool in archaeology, since the dates of some eruptions are well-established.