Christopher M. Stevenson

High precision measurement of obsidian hydration layers on artifacts from the Hopewell site using secondary ion mass spectrometry

Obsidian hydration dating has served as one of the chronological indicators for the Hopewell Culture earthworks (ca. 200 B.C.—A.D. 500) in central Ohio. This work presents new obsidian hydration dates developed from high precision hydration layer depth profiling using secondary ion mass spectrometry (SIMS). These data suggest that long-distance exchange in obsidian occurred throughout the Hopewell period.

Prehistoric Agricultural Production On Easter Island (Rapa Nui), Chile

A survey of the Easter Island landscape has resulted in the recognition of numerous lithic mulched household gardens and fields. It is proposed that lithic mulching was a technological innovation introduced to enhance the moisture retention capacity of the excessively drained island soils, and was an innovation incorporated into elite managed field systems which arose in the early 15th century to meet the demands for surplus production.

Variation in Rapa Nui (Easter Island) land use indicates production and population peaks prior to European contact

Significance Our paper evaluates a long-standing debate and examines whether the prehistoric population of Rapa Nui experienced a significant demographic collapse prior to European contact in AD 1722. We have used dates from hydrated obsidian artifacts recovered from habitation sites as a proxy for land use over time. The analysis suggests region-specific dynamics that include the abandonment of leeward and interior locations. These temporal land-use patterns correlate with rainfall variation and soil quality. This analysis demonstrates that the concept of “collapse” is a misleading characterization of prehistoric human population dynamics. As a result, we see our approach as useful in the study of other prehistoric societies for which a sudden demographic collapse has been proposed in prehistory. Many researchers believe that prehistoric Rapa Nui society collapsed because of centuries of unchecked population growth within a fragile environment. Recently, the notion of societal collapse has been questioned with the suggestion that extreme societal and demographic change occurred only after European contact in AD 1722. Establishing the veracity of demographic dynamics has been hindered by the lack of empirical evidence and the inability to establish a precise chronological framework. We use chronometric dates from hydrated obsidian artifacts recovered from habitation sites in regional study areas to evaluate regional land-use within Rapa Nui. The analysis suggests region-specific dynamics including precontact land use decline in some near-coastal and upland areas and postcontact increases and subsequent declines in other coastal locations. These temporal land-use patterns correlate with rainfall variation and soil quality, with poorer environmental locations declining earlier. This analysis confirms that the intensity of land use decreased substantially in some areas of the island before European contact.

Rain, Sun, Soil, and Sweat: A Consideration of Population Limits on Rapa Nui (Easter Island) before European Contact

The incongruity between the small and apparently impoverished Rapa Nui population that early European travelers encountered and the magnificence of its numerous and massive stone statues has fed a deep fascination with the island. Ethnographic and archaeological evidence suggest that the indigenous population was previously greater than the estimated 1500-3000 individuals observed by visitors in the 18th Century. Our goal was to determine the maximum population that might have lived on the island by estimating its agricultural productivity in the time before European contact. To determine the agricultural potential of the island we sampled soils and established six weather stations in diverse contexts and recorded data over a 2-year period. We find that the island is wetter on average than previously believed. We also find that rainfall and temperature respond linearly to elevation, but a spatial model of precipitation requires correction for a rain shadow effect. We adapted to Rapa Nui an island-wide spatial model designed to identify agriculturally viable zones elsewhere in Polynesia. Based on functions relating climate and substrate age to measurements of soil base saturation, we identified 3,134 ha that were suitable for traditional dryland sweet potato cultivation, or about 19% of the 164 km2 island. We used a nutrient-cycling model to estimate yields. Modeled yields are highly sensitive to nitrogen (N) inputs and reliable estimates of these rates are unavailable, requiring us to bracket the rate of N inputs. In the case of low N availability, yields under continuous cultivation were very small, averaging 1.5 t/ha of wet sweet potato tuber. When the N fixation rate was quadrupled sustainable yields increased to 5.1 t/ha. In each N scenario we used a model of food-limited demography to examine the consequences of altering agricultural practices, the labor supply, the ability of the population to control its fertility, and the presence or absence of surplus production to support social inequalities. In the low-N case viable populations average approximately 3,500 individuals across all parameter combinations, versus 17,500 in the high-N case, although sustainable populations in excess of 25,000 were possible under some assumptions.

Prehistoric Obsidian Exchange on Rapa Nui

ABSTRACT The four sources of rhyolitic obsidian on Rapa Nui (Maunga Orito, Moti Iti, Rano Kau I [Te Manavai], Rano Kau II) were differentially utilized throughout prehistory (ca. AD 1200–1860). In order to document the nature of quarry exploitation and obsidian distribution, energy dispersive X-ray fluorescence was used to characterize the elemental composition of each source. The classification of 331 archaeological samples from inland habitation sites, ritual centers, and crematoria by discriminant analysis revealed selective patterns of obsidian usage. Obsidian from Rano Kau II was rarely used while Maunga Orito and Rano Kau I glasses were present in nearly equal proportions at inland domestic habitation sites. Motu Iti obsidian was a rare occurrence at interior locations but more frequent at coastally located ritual centers, crematoria, and caves. Surface architecture in the form of an elite house at Maunga Orito, restricted source usage, and the sacred nature of the offshore islets, suggested an elite managerial presence at two quarries in the distribution of obsidian to the island population during prehistory.

Response: Commentary: Rain, Sun, Soil, and Sweat: A Consideration of Population Limits on Rapa Nui (Easter Island) before European Contact

Citation: Puleston CO, Ladefoged TN, Haoa S, Chadwick OA, Vitousek PM and Stevenson CM (2018) Response: Commentary: Rain, Sun, Soil, and Sweat: A Consideration of Population Limits on Rapa Nui (Easter Island) before European Contact. Front. Ecol. Evol. 6:72. doi: 10.3389/fevo.2018.00072 Response: Commentary: Rain, Sun, Soil, and Sweat: A Consideration of Population Limits on Rapa Nui (Easter Island) before European Contact