Cation ratio dating is used to date rocks that have a modified surface such as prehistoric rock carvings (petroglyphs). This is a relative dating technique and is not considered to be an accurate method of dating in some professional views.

Rocks are covered by a kind of varnish, a chemically-changed layer caused by weathering that builds up over time. The change in the rock varnish is due to calcium and potassium seeping out of the rock. The cation ratio is determined by scraping the varnish from the carved or petroglyph surface back to the original rock surface and making a comparison of the two using a positively charged ion. Like dendrochronology, this ratio is affected by soil and moisture. Thus, a leaching curve is created by geographical area.

Bibliography

http://www.rlc.dcccd.edu/mathsci/anth/231/datetext.htm#9.5

http://www.une.edu.au/Arch/ROCKART/Dating.html

By: Joel R. Siebring