Introduction to The Tutorial

Using technology invented in Hawaii, the Polynesian people developed an aquacultural system that, at the time of the first European contact in 1778, consisted of many hundred fishponds.  In recent years, archaeologists have excavated well stratified deposits relating to the creation of the fishponds and, in so doing, have obtained a considerable number of organic samples suitable for radiocarbon dating.  For this tutorial we consider one of these, at which 5 organic samples were excavated and submitted to a radiocarbon laboratory for dating.

Defining the a priori chronological information

The archaeologists who worked on the fishpond identified three phases associated with its creation and use.  The earliest phase, Layer III, is considered to be of pre-fishpond origin and gave rise to one of the five organic samples submitted for radiocarbon dating.  Layer II, the next phase, represents the pond developed by the Polynesians.  This phase gave rise to the four other samples submitted for radiocarbon dating.  The relative chronological order of the samples within this phase is unknown.  National archive photographs show the pond being filled in 1941 AD.  This represents the start of the latest phase, Layer I, from which there are no dated samples.

Archaeological evidence suggests that Layer III abuts and is earlier than Layer II, which in turn abuts and is earlier than Layer I.  We can define these relationships as abutting because there is no evidence for hiatuses between the phases or for overlap (BCal allows for both such phase relationships if required).

The arrival of the Polynesians can be identified in the above chronology.  They must have arrived before the creation of the pond (Layer II), since they created it.  Therefore the start of Layer II (which is contemporary with the end of Layer III), must be later than the arrival of the Polynesians.  Given interpretations of the archaeological record for the region, the archaeologists' best estimate for the date of the arrival of the Polynesians can be represented as a normal distribution with a mean of 600 AD and a standard deviation of 100 years.

The organic samples and their radiocarbon data

The following table summarises the information about the organic samples and their associated radiocarbon data.
Laboratory no. Radiocarbon determination Material dated Layer Origin
4128 2816±74 humus Layer III atmospheric
4127 440±160 sediment Layer II marine
4126 630±150 sediment Layer II marine
4125 370±140 sediment Layer II marine
4124 360±180 sediment Layer II marine

Two important issues should be raised about the radiocarbon data.  Firstly, as expressed in the table, the organic sample from Layer III metabolised in an atmospheric environment.  This is different to the other samples, which metabolised in a marine environment.  Secondly, because some of the samples metabolised in a marine environment, delta-R reservoir corrections must be applied to them.  The recommended delta-R offset for Hawaii is 110±80 (Dye 1994).


T. Dye, Apparent Ages of Marine Shells: Implications for Archaeological Dating in Hawai`i.  Radiocarbon 36(1):51-57 (1994)