Standard evaluations of bomb curves and age calibrations along with consideration of environmental and biological variability show the rigor of phytolith dates on modern neotropical plants: Review of comment by Santos, Alexandre, and Prior

Publication date: July 2016
Source:Journal of Archaeological Science, Volume 71
Author(s): Dolores R. Piperno
Santos et al. claim that a recent phytolith 14C study by Piperno of Neotropical plants that grew during the post-bomb era provided anomalously old ages due to 14C depletion. They argue the depletion source is likely old carbon in soils transported into plants via root uptake. Here I show: 1) their claims for anomalous 14C depletions in phytoliths are unfounded because they fail to consider uncertainties created in the bomb curve from local and regional environmental variability and other factors shown to lead to bomb curve offsets in post-bomb 14C study, 2) they error by not calibrating the phytolith dates, a standard procedure with post-bomb 14C determinations, 3) they inexplicably consider an ancient (1640 14Cyr B.P) age for one of the dated samples to be accurate when (a) it is known the sample was treated with substances made from fossil fuels that were not removed with the extraction process, and (b) the amount of radiocarbon dead carbon required to generate the ancient age from SOM is unreasonable, and 4) their theory that old soil carbon from root uptake is sequestered in phytoliths causing significant skews to phytolith ages is not supported by accumulated evidence from ancient, and now modern Neotropical contexts.