For absolute dating of archeological artifacts, the radiocarbon method emerged during the latter half of the twentieth century as the most reliable and precise method. The results of obsidian (volcanic glass) dating, a method based on the belief that newly exposed obsidian surfaces absorb moisture from the surrounding atmosphere at a constant rate, proved uneven. It was initially thought that the thickness of the hydration layer would provide a means of calculating the time elapsed since the fresh surface was made. But this method failed to account for the chemical variability in the physical and chemical mechanism of obsidian hydration. Moreover, each geographic source presented unique chemical characteristics, necessitating a trace element analysis for each such source. Yet despite its limitations, obsidian dating helped archeologists identify the sources of many obsidian artifacts, and to identify in turn ancient exchange networks for the flow of goods. Nor were ceramic studies and fluoride analysis supplanted entirely by the radiocarbon method, which in use allows for field labeling and laboratory errors, as well as sample contamination. In addition, in the 1970s, dendrochronological (tree-ring) studies on the bristle cone pine showed that deviation from radiocarbon values increases as one moves back in time. Eventually calibration curves were developed to account for this phenomenon; but in the archeological literature we still find dual references to radiocarbon and sidereal, or calendar, time.The author mentions all of the following as problems with radiocarbon dating EXCEPT for
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The Andean cordillera is made up of many interwoven mountain ranges, which include high intermundane plateaus, basins, and valleys. The Northern Andes contain several broad ecosystems falling into four altitudinal belts. Its northern subregion is distinguished by higher humidity and by greater climatic symmetry between eastern and western flanks. The Central Andes are characterized by a succession of agricultural zones with varied climatic conditions along the mountains flanks and by large, highaltitude plateaus, variously called puna or altiplano, which do not occur in the Northern Andes. The soil fertility of the northern altiplano is generally good. The western Central Andean ranges are relatively arid with desert-like soils, whereas the eastern ranges are more humid and have more diverse soils. The eastern slopes of the Central Andes in many ways are similar to the wet forests of the Northern Andes. Unlike the Northern Andes, however, these slopes have a dry season. In regions of gentle topography, such as the Amazon basin, regional climatic variation can be determined from a few widely spaced measurements. Regional projections in the Andean cordillera are quite difficult by comparison. For example, while air temperature generally decreases with increasing altitude, variability of mountain topography can produce much lower than expected air temperatures. Nevertheless, some general climatic patterns are discernible. For example, with increasing distance south of the equator the seasonality of precipitation increases, whereas the total annual amount generally decreases. Humidity commonly increases with increasing altitude, but only to some intermediate altitude, above which it declines. The variability of mountain terrain also affects precipitation, such that conditions of extreme wetness and aridity may exist in close proximity. Related to this temperature gradient is a pattern of greater rainfall at the valley heads, and less rain at lower altitudes, resulting in part from mountain rainshadow effect. The weather patterns of theAndean cordillera and Amazon basin in general reflect movements of highand low-pressure cells associated with the Intertropical Convergence Zone, a low- pressure trough that moves further north and south on a seasonal basis. Precipitation is high throughout the year in the highlands and on the coast in the NorthernAndes. Coastal aridity increases south of central Ecuador, culminating in the Atacama desert of northern Chile. In the Central Andes, highland precipitation is seasonal, and amounts are approximately half those measured in the Northern Andes. The aridity of the Central Andean coastal zone is the result of the drying effect of the cold Pacific Humboldt current and the southern Pacific high-pressure cell. Much of the southern portion of the Central Andes in Bolivia is also arid.The dry season causes soil moisture deficits and diminished stream flow part of each year.The passage is primarily concerned with
Personality is rooted as deeply in the need for _______, or at least personal interaction, as _______ well-being is rooted in chemical needs.
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