Age Range and Optimum Resolution

Basis of Method and Remarks






11. Amino acid racemization



Requires shell or skeletal material. Based on release of amino acids from protein and subsequent inversion of their stereoisomers. Shells tend to be more reliable than bone, wood, or organic-rich sediment. Is strongly dependent on other variables, especially temperature and leaching history. Commonly used as a relative dating or correlation technique, but yields numerical ages when calibrated by other techniques.

12. Obsidian hydration



Based on thickness of the hydrated layer along obsidian crack or surface formed during given event. Age proportional to the thickness squared. Calibration depends on experimental determination of hydration rate or numerical dating. Subject to errors due to temperature history and variation in chemical composition.

13. Tephra hydration



Requires volcanic ash. Based on the progressive filling of bubble cavities in glass shards with water. Subject to the same limits as obsidian hydration, plus others, including the geometry of ash shards and bubble cavities.

14. Lichenometry

X to XXX


Requires exposed, stable rock substrates suitable for lichen growth. Most common in alpine and arctic regions, where lichen thallus diameter is proportional to age. Subject to error due to climatic differences, lichen kill, and misidentification. The limit of the useful range varies considerably with climate and rock type.

15. Soil development



Encompasses a number of soil properties that develop with time, all of which are dependent on other variables in addition to time (parent material, climate, vegetation, topography). Is most effective when these other variables are held constant or can be evaluated. Precision varies with the soil property measured; for example, accumulation of soil carbonate locally yields age estimates within ±20 percent.

16. Rock and mineral weathering



Includes a number of rock and mineral-weathering features that develop with time, such as thickness of weathering rinds, solution of limestone, etching of pyroxene, grussification of granite, and buildup of desert varnish. Has the same basic limitations as soil development. Precision varies with the weathering feature measured.

17. Progressive landform modification



In addition to time, depends on factors such as climate and lithology. Depends on reconstruction of original landform and understanding of processes resulting in change of landform, including creep and erosion.

18. Rate of deposition



Requires relatively constant rate of sedimentation over time intervals considered. Numerical ages based on sediment thickness between horizons dated by other methods. Quite variable in alluvial deposition.

19. Geomorphic position and incision rate



Geomorphic incision rates depend on stream size, sediment load, bedrock resistance to erosion, and uplift rates or other base-level changes. If one terrace level is dated, other terrace levels may be dated assuming constant rate of incision.

20. Rate of deformation



Dating assumes deformation rate constant over interval of concern and requires numerical dating for calibration. At spreading centers and plate boundaries, nearly constant rates may be valid for intervals of millions of years.

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