Reasons for uncertainty about the timing of the Thule migration [the movement of a proto-Inuit culture from Alaska to northern Canada and Greenland] are many, but primary among them are the well-known problems with radiocarbon dating in the Arctic. In particular, radiocarbon dates obtained on two kinds of organic remains that typically are common in the remains of Thule dwellings driftwood and sea mammal bone--are likely to be older than the archaeological context in which they are found. Driftwood found in archaeological sites in the form of fuel or as part of an artifact assemblage may have sat on beaches for centuries before being utilized, and sea mammal bone is subject to the marine reservoir effect in which living tissue(including bone) incorporates ancient carbon, which also results in dates that are too old. Beyond this, however, many dates obtained in decades past simply seem too old, and there is a widespread suspicion among archaeologists that pretreatment methods may not always have eliminated the presence of substances derived from sea mammals, especially fat, which can be absorbed into wood, bone, and other materials and thereby contaminate them. As a result of these and other factors, both MeGhee and Park have shown that the full spectrum of existing Thule radiocarbon dates, numbering in the hundreds, covers much too wide a range to reflect Thule chronology accurately.