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 would probably consider which of the following the LEAST likely means of dating archeological artifacts?
Mark Twain and Garrison Keillor were both born and bred in Midwestern America; yet the themes, writing styles, and attitudes of these two humorists are_______.
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