In this series, we've talked about the various methods archaeologists use to determine the dates of occupation of their sites. As you've read, there are several different methods of determining site chronology, and they each have their uses. One thing they all have in common, though, is they cannot stand alone.
Each method that we've discussed, and each of the methods we haven't discussed, may provide a faulty date for one reason or another.
Radiocarbon samples are easily contaminated by rodent burrowing or during collection.
Thermoluminescence dates may be thrown off by incidental heating long after the occupation has ended.
Site stratigraphies may be disturbed by earthquakes, or when human or animal excavation unrelated to the occupation disturbs the sediment.
Seriation, too, may be skewed for one reason or another. For example, in our sample we used the preponderance of 78 rpm records as an indicator of relative age of a junkyard. Say a Californian lost her entire 1930s jazz collection in the 1993 earthquake, and the broken pieces ended up in a landfill which opened in 1985. Heartbreak, yes; accurate dating of the landfill, no.
Dates derived from dendrochronology may be misleading if the occupants used relict wood to burn in their fires or construct their houses.
Obsidian hydration counts begin after a fresh break; the obtained dates may be incorrect if the artifact was broken after the occupation.
Even chronological markers may be deceptive. Collecting is a human trait; and finding a Roman coin a ranch style house which burned to the ground in Peoria, Illinois probably doesn't indicate the house was built during the rule of Caesar Augustus.
Resolving the Conflict with Context
So how do archaeologists resolve these issues? There are four ways: Context, context, context, and cross-dating. Since Michael Schiffer's work in the early 1970s, archaeologists have come to realize the critical significance of understanding site context. The study of site formation processes, understanding the processes that created the site as you see it today, has taught us some amazing things. As you can tell from the above chart, it is an extremely crucial aspect to our studies. But that's another feature.Secondly, never rely on one dating methodology. If at all possible, the archaeologist will have several dates taken, and cross check them by using another form of dating. This may be simply comparing a suite of radiocarbon dates to the dates derived from collected artifacts, or using TL dates to confirm Potassium Argon readings.
I believe it is safe to say that the advent of absolute dating methods completely changed our profession, directing it away from the romantic contemplation of the classical past, and toward the scientific study of human behaviors. Not everybody is happy with this change, but it is a change towards science nonetheless.
Thanks go to reader Roger Hall, for suggesting the series, and to Douglas Frink, for lending a hand when I needed one.
