Archaeology and the Importance Inventory Digitization

“. . . to foster understanding. . .”

I like this phrase because it is at once both purposeful and aspirational. The words are found towards the bottom of a poster hanging on a wall in my studio apt. The image in the poster is a rendering of world-renowned artist Christo’s massive art installation, “Wrapped Reichstag”. In the context of the poster, the phrase refers to a renewed effort to nurture communication and understanding between the young people of North America and Germany in the years immediately following the fall of the Berlin Wall. 

 “Wrapped Reichstag”

Lately, during the last four months specifically, a broadened interpretation of this phrase has become a source of inspiration for me during the many hours of monotonous and repetitive data entry. And that has been the order of the day for months now: data entry. More specifically, the digitization of artifact inventories on paper, many of them handwritten 35, 50 or more years ago. Line after line, site number, catalog number, northings and eastings, depth, artifact description, quantity and so on. Why is this important to do? Ah yes, look to the poster!

The purpose of this inventory digitization is twofold. The first is digitization as a means of preservation. Paper yellows and becomes brittle, ink and pencil fade over time, and information would eventually be lost were it not transferred to another medium. The second purpose is accessibility. One cannot know if information is applicable or relevant to their lives if they do not have access to it. Digitization is a first step toward facilitating greater availability of this information to everyone. Fewer gates, and fewer gatekeepers.  A democratization of data, perhaps which, with a healthy dose of optimism has the potential (you guessed it) - to foster understanding.

And therein lies another aspect of this quote – as it is a call to action.  This call to action has only been partially realized by the opening up of stored information that was once restricted to those of a certain socio-economic pedigree (read education). In other words, the careful control of information flowing in a top down fashion as many institutions tend to do, oftentimes protects a prevailing narrative/interpretation that reinforces their own legitimacy within the larger societal structure, for better or worse.

To fulfill this call, the equally necessary flip side of this imperative is to engage in the act of listening to multiple interpretations. Listening is often viewed as a passive behavior, but if we are truly striving “to foster understanding”, participants must engage in active listening. Active listening is not always easy. It requires patience and empathy and a willingness to be exposed to experiences and ideas that are divergent, or even outright antithetical to one’s own worldview, which understandably can be uncomfortable. It is a skill set like any other, that must be developed and maintained in order to be effective. The reward for this effort is the possibility of creating not only a more inclusive and thereby more accurate narrative, but also a more meaningful one.

Archaeologists are concerned about the preservation of sites and have strived to serve as stewards of archaeological sites and the associated data. Why shouldn’t this data (excepting sensitive location information) be freely shared with others? How are site security concerns of archaeologists balanced with the curiosity of the general public? Preservation of sites and data are at the core of the Historic Preservation movement enacted by law in 1966 and a key component to our training.  If we protect these resources from destruction either through development or looting- we preserve them for the future.  We don’t know what our immediate future will look like, but as in all measures of preservation, we are protecting resources for hundreds or thousands of years to come. Evaluating human behavior through the scientific analysis of the archaeological record is critical for our ability to prepare and predict adaptation and culture change in an ever-changing world.  Sharing data regarding these sites and resources requires an open communication process that understands the desire to learn and in exchange, garners the respect and understanding of the scientific analysis produced. 

Both personally and professionally, this phrase, just three words long, has served as a strong foundation for me these past several months of uncertainty and upheaval, and it is my pleasure to share it with you. I hope it inspires you “to foster understanding” in your endeavors as it has me in mine.

For more information, visit PAarchaeology.state.pa.us or the Hall of Anthropology and Archaeology at The State Museum of Pennsylvania .

Dating Methods: Achieving the Correct Results

Carbon 14, Dendrochronology and Deep Time

This week we are visiting the topic of archaeological time and how two scientific dating methods have vastly enhanced our understanding of past human events.

 It was principally through the research of Willard F. Libby (1908-1980) (Anderson et al. 1947) that the method of radiocarbon dating, an accurate, absolute method of dating organic substances from archaeological, geological and environmental contexts, was developed. A key thresh-hold leading to the radiocarbon dating method was the discovery of the Carbon 14 atom’s half-life of 5,730 years*. By comparing the known decay rate of C14 with the amount of C14 remaining, Libby was able to calculate the age of the sample up to approximately 45,000 to 50,000 years. 

In 1948, following this breakthrough, Libby and a committee of anthropologists and geologists under the sponsorship of the American Anthropological Association tested different organic materials of known ages. For example, the funeral boat cedar wood belonging to the Egyptian pharaoh Sesostris, who died circa 3800 years B.P. (before the present). Libby’s radiocarbon age confirmed the boat’s known age at 3,800 +/-180 B.P. (Arnold and Libby 1949; Libby 1952; Poole 1961). Until Libby’s breakthrough discoveries in the radiocarbon dating process scientists could only estimate the age of archaeological/geological samples through relative means, such as stratigraphy and an artifact’s association with something else. For his pioneering research in the radiocarbon dating method Willard Libby was awarded the Nobel Prize in 1960.

Extracting wood charcoal for carbon dating

Since the discovery of radiocarbon dating its boundaries and accuracy has been enhanced by other scientific disciplines, especially dendrochronology or the study of tree ring patterns (Douglass 1919). Astronomer Andrew E. Douglass (1867-1962) is considered the father of dendrochronology. His scientific approach to correlating annular tree ring growth with solar (sun spot) activity subsequently led to other branches of multidisciplinary studies involving climate change, human use of, and adaptation to, the natural landscape, geological events, art and building history  and other related topics.  On point, is that Douglass developed a precise means by which he could bridge history to prehistory by working backward in time using overlapping tree ring patterns observed in the cross sections of wood beams. Much of his sampling took place at archaeological sites where roof beams were preserved in the arid environment of the prehistoric southwest.  Since Douglass’ pioneering, work much has been accomplished by dendrochronologists to advance the dating method which currently extends the chronology beyond 13,000 years (Ferguson 1970; Schulman 1956; Stuiver et al 1986).

Lab technician with sample specimen for dendrochronology dating 

Radiocarbon Dates + Tree Rings = Calibrated Accuracy

 Graph showing divergence between C14 and tree ring chronologies

                The multidisciplinary approach to dating archaeological samples using C14 and dendrology dating has its limitations and is not the panacea to knowing the exact age of something that has absorbed C14 during its entire life cycle. Fluctuations in the amount of C14, solar radiation, nuclear bomb radiation, volcanic activity etc., to name a few examples, can affect the true C14 age of a sample depending on its age and geographic location and the calibration program(s) used.  Radiocarbon laboratories globally have grappled with the problem by developing their own radiocarbon calibration programs and several of these are available online (i.e OxCal and CALPAL). Through diligence and refinement of these techniques, the applications for dating organic samples can only improve. In light of these improvements in dating methods, The State Museum of Pennsylvania reorganized its culture chronology chart for Pennsylvania.  Based on the recalibrated radiocarbon dates that are now available the following table provides our current culture chronology. Ages following AD.1000 are listed as BP (before present).

* Note: Calculated Libby half-life of C14 is 5568 years. Recalculated true half-life is 5730 years.

References:

Anderson, E.C., W. F. Libby et al.

1947       Natural Radiocarbon from Cosmic Radiation. Physical Review 72:931

Arnold, J.R., and  W.F. Libby

1949       Age Determination by Radiocarbon Content: Checks with Samples of Known Age. Science 110:678.

Douglass, A.E.

1919       Climatic Cycles and Tree Growth. Vol. 1 No. 289, Washington, D.C. Carnegie Institution of Washington.

Ferguson,C.W.

1970       Dendrochronology of Bristlecone Pine, Pinus arisata. Proceedings of the Twelfth Nobel Symposium, Upsala Sweden, August 11-15, 1969. Almquist and Wiksell, Stockholm.

Libby, W.F.

1952       Radiocarbon Dating. University of Chicago Press.

Poole, Lynn

1961       Carbon – 14 and other Science Methods that Date the Past. Whittlesey House. McGraw-Hill Book Company, Inc.


For more information, visit PAarchaeology.state.pa.us or the Hall of Anthropology and Archaeology at The State Museum of Pennsylvania .

Celebrating 60 Years of Using the Carbon 14 Dating Method

Projectile point excavated from the Central Builders site, Northumberland County.
How old is it?

The above projectile point was excavated from a depth of nine feet below the ground surface along with a small group of stone tools and chips produced from the sharpening of tools. They were recovered next to a small cooking hearth with fire altered rock and charcoal. This point is similar to a style of spear point found throughout Virginia and North Carolina but it is slightly different. Based on its excavation depth, it is probably very old.

Prior to the discovery of carbon 14 (C-14) dating by Willard Libby and J. R. Arnold in 1949, we would not know if this spear point was part of the same cultural tradition as similar spear points found below the Mason-Dixon Line or that this one represents a completely different culture. We could only guess at the age and its relationship to other regions or how fast projectile point styles changed.

The discovery of C-14 dating enabled archaeologists to accurately date for the first time prehistoric archaeological materials in much of the world. It was a spectacular discovery and it revolutionized archaeology. With refinements to the method, especially over the past twenty years, we can now determine the age of objects in years before the present (B.P.); we can accurately determine the age of significant events such as the beginning of agriculture or the entrance of humans into the New World; we can compare cultural sequences in widely separated regions of the world; and, most importantly for archaeology, we can measure the rates of cultural change.

from David Hurst Thomas

How Carbon 14 dating works
Carbon 14 is an isotope that is formed when rays from the sun bombard nitrogen molecules in our atmosphere. It acts like other elements such as oxygen or iron, but it is radioactive and therefore, unstable. It behaves just like the stable or non-radioactive form of carbon. All living things contain the stable form of carbon – carbon 12 and the unstable form of carbon – carbon 14. As long as plants and animals are alive, they absorb carbon 14 thereby introducing it into the cells of the body.

However, when an organism dies, the input of C-14 ceases. At the same time, the stable form of carbon remains unchanged in the body. Because C-14 is unstable, over time it returns to a stable form of nitrogen. In 5,730 years, half of the original amount of carbon 14 in an organism will change back to nitrogen. This is called the carbon 14 half-life. Through Libby and Arnlod's discovery, the ratio of stable carbon to unstable carbon can be measured and a date can be calculated to determine the age of the carbon at the time of death. In essence this is how carbon dating works.

A draw back with C-14 dating is that it can only be used on organic material such as wood, bone, or shell –materials that were once parts of plants and organisms. It cannot, unfortunately, be used to directly date stone spear points or pottery and these are, by far, the most common artifacts from prehistory that have survived the vestiges of time. Therefore, archaeologists must date the organic materials directly associated with these non-organic artifacts. Essentially, scientists date the charcoal from the cooking hearth or trash pit with which the artifacts are associated resulting in a proxy date for the non-organic artifact.

The projectile point from the Central Builders site pictured above was associated with charcoal from the cooking hearth that radiocarbon dated to 9165 + 210 B.P. (University of Arizona Laboratory #10053). What does this mean? First, the University of Arizona facility performed the analysis and the sample number was 10053. The letters “B.P.” are an abbreviation for Before the Present. But that is not exactly correct because it actually means before the year 1950.

Since the present is always changing, Libby and Arnold decided to use a standard date of 1950 (remember the discovery date of the carbon 14 method was year earlier) as the present. The date of the charcoal is 9165 years before 1950 but this is based on several measurements of the amount of carbon 14 and carbon 12 remaining in the sample. In the University of Arizona sample #10053, the number 9165 is the mean of a number of measurements made by the lab.

This results in a plus or minus factor or standard deviation produced by the laboratory calculations. Therefore, using one standard deviation, there is a 68% chance that the actual date falls between 9375 and 8955 B.P. Usually, archaeologists are looking for a 95% probability and that means the date is somewhere between 9580 and 8745 B.P. This is a range of 835 years, but as we will see next week, this plus or minus factor has been greatly reduced by refining the radiocarbon dating method.

For more information, visit PAarchaeology.state.pa.us or the Hall of Anthropology and Archaeology at The State Museum of Pennsylvania .