Archaeologists must be careful to ensure that the samples they collect for dating are: 1) not contaminated and; 2) found in situ (i.e., in the place where they were originally deposited).
In addition, because samples are expensive to date and time consuming to collect and prepare for submission, archaeologists must carefully consider which samples to date and how many. To ensure the accuracy of dates from a particular site and to build good, consistent chronologies:
- the samples submitted should be from short-lived species. Why?
- multiple samples from the same stratigraphic context and site should be dated. Why?
- the samples should not be culturally ambiguous (i.e., not in association with cultural material). Why?
Look at the photos and captions below. What issues might you encounter when sampling?
Archaeologists in New Zealand often collect radiocarbon samples from features like this underground oven or hangi which was exposed in profile by erosion. Small ovens are common features at these sites. Note the concentration of charcoal near the base of this feature.
This is a coastal profile at a site in the Caribbean.
What methods have archaeologists devised here to take samples?
From where might you collect samples?
This is a posthole feature in another coastal profile where prehistoric peoples dug a hole to place a wooden timber for constructing a house.The dark “v-shaped” outline is typical of postholes found at archaeological sites and is a result of soil mixing and wood decomposition. Would this be a good place to sample? Why or why not?
To better recover smaller site constituents, excavated soil may be dumped into wire mesh screens and sifted either directly in the ocean or by washing the soil away using hoses from a water pump. Could or would you collect charcoal samples using this method? Why or why not?
Cross-section of Pittosporum wood from New Zealand.
Wood charcoal samples may be submitted to wood charcoal specialists so they can be identified to the plant species. Long-lived taxa like bristle cone pine or driftwood originating from another continent might provide problematic results. Would this be a good idea to do all of the time?
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