Tag Archives: archaeology

Reconstructing the proteome of ancient peoples in soils

Soils are often one of the most common archaeological artifacts, and the clay minerals contained within soils have a unique ability to tightly bind proteins, slowing or preventing their decomposition. For this reason, a fraction of proteins added to a soil during human occupation can potentially be retained for hundreds or thousands of years, serving as a “protein fingerprint” that may shed light on the diet, agricultural activities, livestock, or even human populations themselves that inhabited region.

A recent study attempts to use mass spectrometry techniques to characterize the proteinaceous matter residing in soils from excavated farmhouses of Roman origin in the present-day Netherlands. Using a novel approach termed “peptide-mass fingerprinting”, the researchers were able to uncover a suite of keratinaceous proteins commonly found in human hair and skin fragments.

Characterizing the proteins present in living tissues has been common practice in the biomedical world for at least two decades. The application of proteomics to complex environments such as soils is, by contrast, novel, and this study represents the first published attempt to use proteomics as a fingerprinting tool in an archaeological soil. I could easily see this technique becoming valuable in reconstructing the history of not just soils, but any structures or artifacts produced from clays, as clay minerals in soils are one of the key protein-binding agents. If certain protein classes in soils, for instance keratinaceous skin proteins, could be distinguished into different isoforms, or classes, based on their molecular weight, then these protein fingerprints could be related to extant proteins.Taking this one step further, different protein isoforms are often associated with genetically distinct populations of organisms. If we could begin relating ancient protein fingerprints to their extant counterparts, we might be able to indirectly trace the human genetic history of a site or an object.

Oonk et al. 2012. Soil proteomics: An assessment of its potential for archaeological site interpretation. Organic Geochemistry, 50, 57-67.

Mountain glaciers become sea water, frozen tombs uncovered

Over the past several decades, the rapid melting of mountain glaicers has been a primary contributor to rising sea levels. Estimates of the long-term contribution of non-polar glacial melting to sea level rise vary substantially, but most experts agree that the contribution will fall somewhere between a tenth and a third of a meter. A recent Nature Geoscience report used the World Glacier Inventory, a repository of information on >120,000 glaciers, to predict changes this century in all 19 non-polar regions containing mountain glaciers and ice caps. This study predicts that total glacial volume will reduce by 21 +/- 6% by 2100, though in certain areas the reduction may be as high as 75%. This will lead to dramatic changes in regional hydrology and serious water problems for people who depend on seasonal glacial melting for freshwater and irrigation (see my December post, “Fog harvesting for a thirstier world”).

Water shortages, sea level rise, and erosion and hydrologic changes resulting from mountain glacial melting all pose real and very apparent problems for human populations. Another fascinating result of glacial melting will not incite new environmental dangers, but is already leading to social unrest and conflict between scientists and indigenous populations. It turns out that in certain regions, tombs, bodies and ruins from ancient civilizations, once buried deep beneath the ice, are now thawing. The most prominent example of this is in the Central Asian Altai mountains, where over 700 tombs have been preserved for 2,500 years by ice or permafrost. Increasing ground surface temperatures are causing these tombs to thaw. Another example is the huge coastal cemetery near Barrow, Alaska, where sea ice loss is causing the coastline to erode at rates of up to 20 m/year, exposing generations of human remains. It is becoming apparent that glacial thawing will impact frozen archaeology worldwide, and will potentially lead to both great discoveries and great unrest.

Globally, some of the most fascinating human archaelogical discoveries have involved frozen remains. Freezing allows preservation of human tissue that would otherwise decay in several decades, and archaelogists are now using advanced molecular techniques to date such tissue and even extract ancient DNA samples. Archaeologists across the world are now clamoring to take advantage of newley exposed human remains that may only be valuable for a short period of time. This has already stirred anger amongst many indigenous populations, who do not wish to see their ancestor’s remains and a part of their cultural heritage uprooted and shipped off to a lab thousands of miles away for chemical analysis.

The problem essentially arises from the fact that there is currently no standard legal framework to mediate the interests of scientists, governments and indigenous people with respect to these precious archaeological repositories. Glacial retreat necessitates the creation of new laws and policies to address these concerns- and soon, if our mountain melting rate predictions are at all accurate.

Radick and Hock. 2011. Regionally differentiated contribution of mountain glaciers and ice caps to future sea-level rise. Nature Geoscience. In press.

Molyneaux and Reay 2011. Frozen archaeology meltdown. Correspondence . Nature Geoscience. In press.

The rise and fall of human society with climate change

Scientists are becoming increasingly skilled at reconstructing past climates through use of a variety of “climate proxies”, including ice cores, lake sediments, fossils and tree pollen assemblages. Dendochronology, the analysis of tree rings, is now providing powerful evidence for the connection between human welfare and climate. Climate variations have influenced agricultural productivity, warfare and health of preindustrial peoples. A recent study in Science reports a high-resolution reconstruction of Central European summer precipitation and temperature for the past 2500 years, providing direct evidence that periods of social stability correspond with climactic stability, while periods of social upheaval, famine and even plague correspond with dramatic climate shifts and increased climactic variation.

To reconstruct a long-term climate record, researchers examined nearly 9000 pieces of wood from living and dead trees. Over 7000 were oak samples from France and Germany. Many of these were collected from historic buildings, or rivers and bogs that preserve ancient wood. To obtain the earliest dates possible, samples were obtained from archaeological sites. Researchers separately collected 1500 stone pine and larch wood samples from high altitudes in Austria.

To make a continuous record from the present to the past, dendochronologists first examine tree rings from live wood samples to provide a baseline for dating. From there they work back to older and older samples. The width of spacing between consecutive rings corresponds to the amount of growth experienced that year. In particularly bad years, a ring may be broken, fuzzy, or barely present. The isotopic composition of wood samples can also be taken and several important climate metrics can be extracted from it. O18, for example, is a heavy isotope of oxygen. In rainy years, paleoclimatologists expect a sample to be relatively enriched in O18. Taken together, these two sources of data provide strong evidence for both temperature and moisture conditions in a particular year.

To calibrate such a climate record, human records are extremely valuable. Weather records providing temperature and moisture data over the past 200 years were collected for Central Europe. These records allow scientists to precisely determine how weather affects ring growth in that year.

The result?  A continuous, 2500-year climate record that, when compared with archaeological and historical data, showed a stark pattern. Times of social stability and prosperity corresponded with warm, wet summers that led to high agricultural yields. Warm, stable climates coincide with the rise of the Roman Empire and peak years of medieval Europe. The opposite was also true. For example, a dramatic cold snap around ~1300 A.D. occurred directly prior to the famines and plague that spread across Europe half a century later. The decline of the Holy Roman Empire from AD ~250-600 coincides with a marked increase in climactic variability.

Though ancient peoples were clearly more susceptible to the affects of a bad harvest year than modern societies are, the powerful and fundamental connection between human welfare and climate still manifests itself today. Many scientists believe that the Holocene, the geological era of relatively mild, stable climates that led to the global dominance of the human species, is now ending. The Anthropocene, an era in which human actions are the primary climate driver, has just begun. We may do well to consider the effect of climate on human society throughout a climactically stable era when making decisions that will affect our climate in the future.

 

Buntgen et al. 2011. 2500 Years of European Climate Variability and Human Susceptibility. Science. In press.