W.J. Rink

Geochronology of cave deposits at Liang Bua and of adjacent river terraces in the Wae Racang valley, western Flores Indonesia: a synthesis of age estimates for the type locality of Homo floresiensis

A robust timeframe for the extant cave deposits at Liang Bua, and for the river terraces in the adjoining Wae Racang valley, is essential to constrain the period of existence and time of extinction of Homo floresiensis and other biota that have been excavated at this hominin type locality. Reliable age control is also required for the variety of artifacts excavated from these deposits, and to assist in environmental reconstructions for this river valley and for the region more broadly. In this paper, we summarize the available geochronological information for Liang Bua and its immediate environs, obtained using seven numerical-age methods: radiocarbon, thermoluminescence, optically- and infrared-stimulated luminescence (collectively known as optical dating), uranium-series, electron spin resonance, and coupled electron spin resonance/uranium-series. We synthesize the large number of numerical age determinations reported previously and present additional age estimates germane to questions of hominin evolution and extinction.

Confirmation of a near 400 ka age for the Yabrudian industry at Tabun Cave, Israel

Abstract The important Lower and Middle Palaeolithic site of Tabun has been previously dated using ESR, U-series and TL. ESR ages throughout the site are substantially younger than TL dates, although these methods have been shown to agree at other sites in Israel and elsewhere. All previous ESR dates have been obtained on museum specimens using only attached sediments for dosimetry. Here we report the first ESR and U-series analyses of a tooth found in situ in an area equivalent to the lowest part of layer Ed. We obtain a combined ESR/U-series age of 387+49−36ka, in good agreement with a TL age of 340±33 ka for similar levels, and substantially older than an ESR/U-series age using attached or nearby sediment for dosimetry. We conclude that the most likely explanation for the previous shorter ESR chronology was the use of inappropriate gamma dose rates based on sediments attached to teeth.

Progress in ESR and U-Series Chronology of the Levantine Paleolithic

Any study of the origins of humans must be set in a chronological context. Prehistorians now have available to them a reasonably large set of tools with which to assign ages to events of the past. Radiocarbon is essentially useless as a tool for the time range under discussion here: In samples older than about 40 ka, the atoms originally deposited with the sample have decayed to less than 1% of their initial value, while equal or greater amounts of contaminant atoms may be present. Newer dating methods now exist which are based on the measurement of doses of radioactivity trapped in natural or artificial materials. While these methods can span the time range, they can also extend much further back in time, and are applicable to a wide variety of archaeological deposits. While their normal precision of 10% is much less than that of dating, they do not require independent calibration. These methods encompass the following: thermoluminescence (TL) dating of burned flint artifacts (Valladas et al., this volume); opticaland infrared-stimulated luminescence (OSL, IRSL) dating of wind-blown sand and silt (e.g., desert loess) which has been zeroed by solar bleaching; and electron spin resonance (ESR) dating of tooth enamel of larger mammals. Some of the physical parameters used to determine the age are shared by all these methods (external dose rate, water content of sediment) while others are unique to each method and sample type (e.g., internal dose rate) and assure that these various methods provide dates that are largely independent of one another. For example, ESR ages at a site may largely depend on the internal uranium content of the tooth sample and its uptake history, whereas TL dates on flint at the same site may depend equally on internal and external dose rates. Over the past decade there has also been an order-of-magnitude increase in the precision of uranium-series (US) dating through the advent of thermal ionization mass spec-