Oxidizable Carbon Ratio is an easy, inexpensive, and accurate chemical procedure that provides a physiological profile of the soil body and its behavior through time. It is also used to establish the age of specific cultural features along with post-cultural abandonment changes that have occurred at a particular site. The OCR dating technique was introduced in 1992 by the Archaeology Consulting Team from Essex, VT. It was developed to measure the site-specific rate of biodegradation of carbonized organic matter that has resulted from human activity, either as soil humic material or charcoal, that can be found in soil.

Humus and charcoal, unlike some organic matter, are biologically recycled at a very slow rate that follows a linear progression through time with an increase in readily oxidizable carbon and a decrease in the total amount of organic carbon. There are two chemical analysis used to determine the OCR of a soil sample. One is the Walkley-Black wet combustion procedure (1935), which measures the readily oxidizable carbon within a sample. The other one is the Ball loss on ignition procedure (1964), which measures the total carbon of a sample. When the results of these two measurements are put together a ratio of total carbon to readily oxidizable carbon is expressed, the OCR.

The OCRdating technique differs epistemologically from that of radiocarbon dating. Radiocarbon dating follows the classic physics model of entrophy, where they measure the decay of unstable carbon isotopes. The OCR procedure, on the other hand, describes an evolving pedogenic system that is dynamic and resists entrophy by organizing and maintaining itself far from equilibrium and models this dynamic and nonlinear soil system with the reactivity of the soil’s organic carbon within that system. Even though there are differences between the two they are not considered to be contradictory sciences, but rather more like alternatives to a common idea. In fact studies have indicated a strong correlation between OCR dates and radiocarbon dates, and you can use OCR dates as an independent check on radiocarbon dates, either verifying or refuting it.

Even though OCR has the potential to provide archaeologists and geologists with a method of finding accurate and precise age estimates from organic carbon within soil, it is still new and in the experimental stage. Scientists question both the methods of the procedure and the accuracy of the results, which is common and needed when any new scientific theory arises. Federal and State organizations, museums, Cultural Resource Management companies, archaeologists, pedologists, and geomorphologists are all currently conducting field studies for OCR dating at hundreds of sites in Northeastern North America and in parts of Europe.

Bibliography

Oxidizable Carbon Ratio Home Page http://members.aol.com/dsfrink/ocr/ocrpage.htm

Archaeology.org, Rmiz OCR http://www.comp-archaeology.org/DougRmizOCRSAA1999.htm

SAA Bulletin 17(5): Point/Counterpoint- OCR Dating, http://anth.ucsb.edu/SAABulletin/17.5/saa18.html

Written By: Jeff Hertaus