Kurt Rademaker

Early maize agriculture and interzonal interaction in southern Peru

Over the past decade, increasing attention to the recovery and identification of plant microfossil remains from archaeological sites located in lowland South America has significantly increased knowledge of pre-Columbian plant domestication and crop plant dispersals in tropical forests and other regions. Along the Andean mountain chain, however, the chronology and trajectory of plant domestication are still poorly understood for both important indigenous staple crops such as the potato (Solanum sp.) and others exogenous to the region, for example, maize (Zea mays). Here we report the analyses of plant microremains from a late preceramic house (3,431 ± 45 to 3,745 ± 65 14C bp or ∼3,600 to 4,000 calibrated years bp) in the highland southern Peruvian site of Waynuna. Our results extend the record of maize by at least a millennium in the southern Andes, show on-site processing of maize into flour, provide direct evidence for the deliberate movement of plant foods by humans from the tropical forest to the highlands, and confirm the potential of plant microfossil analysis in understanding ancient plant use and migration in this region.

Paleoindian settlement of the high-altitude Peruvian Andes

Mountain dwellers of the Pleistocene Humans colonized the inhospitable high Andes at least 11.5 thousand years ago. Rademaker et al. unearthed evidence of hunter-gatherer occupation at heights of almost 4500 m in Peru in two open-air sites. The sites contained more than 750 tools, including likely spearheads and scrapers. A nearby rockshelter with sooted ceilings and floor detritus may have been a campsite. The sites were probably used seasonally for hunting vicuña and other high-altitude prey. Science, this issue p. 466 Artifacts and rock shelters indicate hunter-gatherer presence at ~4500 meters above sea level, 12.8 to 11.5 thousand years ago. Study of human adaptation to extreme environments is important for understanding our cultural and genetic capacity for survival. The Pucuncho Basin in the southern Peruvian Andes contains the highest-altitude Pleistocene archaeological sites yet identified in the world, about 900 meters above confidently dated contemporary sites. The Pucuncho workshop site [4355 meters above sea level (masl)] includes two fishtail projectile points, which date to about 12.8 to 11.5 thousand years ago (ka). Cuncaicha rock shelter (4480 masl) has a robust, well-preserved, and well-dated occupation sequence spanning the past 12.4 thousand years (ky), with 21 dates older than 11.5 ka. Our results demonstrate that despite cold temperatures and low-oxygen conditions, hunter-gatherers colonized extreme high-altitude Andean environments in the Terminal Pleistocene, within about 2 ky of the initial entry of humans to South America.

Younger Dryas deglaciation of Scotland driven by warming summers

Significance Resolving the full manifestation of past abrupt climate change is key to understanding the processes driving and propagating these events. As a principal component of global heat transport, the North Atlantic Ocean also is susceptible to rapid disruptions of meridional overturning circulation and thus widely invoked as a cause of abrupt climate variability in the Northern Hemisphere. We assess the impact of one such North Atlantic cold event—the Younger Dryas Stadial—on an adjacent ice mass and show that, rather than instigating a return to glacial conditions, this abrupt climate event was characterized by deglaciation. We suggest this pattern indicates summertime warming during the Younger Dryas, potentially as a function of enhanced seasonality in the North Atlantic. The Younger Dryas Stadial (YDS; ∼12,900–11,600 y ago) in the Northern Hemisphere is classically defined by abrupt cooling and renewed glaciation during the last glacial–interglacial transition. Although this event involved a global reorganization of atmospheric and oceanic circulation [Denton GH, Alley RB, Comer GC, Broecker WS (2005) Quat Sci Rev 24:1159–1182], the magnitude, seasonality, and geographical footprint of YDS cooling remain unresolved and pose a challenge to our understanding of abrupt climate change. Here, we present a deglacial chronology from Scotland, immediately downwind of the North Atlantic Ocean, indicating that the Scottish ice cap disintegrated during the first half of the YDS. We suggest that stratification of the North Atlantic Ocean resulted in amplified seasonality that, paradoxically, stimulated a severe wintertime climate while promoting warming summers through solar heating of the mixed layer. This latter process drove deglaciation of downwind landmasses to completion well before the end of the YDS.

Multi-technique geochemical characterization of the Alca obsidian source, Peruvian Andes

We report results from comprehensive mapping and multi-technique geochemical characterization of obsidian from the Alca source in the Peruvian Andes (15.3°S, 72.7°W), aimed at understanding patterns of extraction and trade in one of the world’s centers of complex civilization. Alca obsidian was among the most economically important and widely distributed volcanic glasses used for stone tool making in South America from ca. 13 ka until recently, yet the geologic source of this material has never been studied comprehensively. Our work establishes Alca as one of the largest obsidian sources in South America and the only Peruvian source known to have patterned intrasource geochemical variability. There are six geochemically distinct Alca subsources exposed from 2710 to 5165 m elevation over >330 km 2 of the highlands, an area nearly seven times larger than previously known. Our results now permit provenance determination of artifacts to specific outcrops. We analyzed 252 geologic samples using energy-dispersive X-ray fluorescence, neutron activation analysis, wavelength-dispersive X-ray fluorescence, and nondestructive, portable energy-dispersive X-ray fluorescence. All techniques distinguish the same six Alca subsources, establishing analytical comparability between geochemical methods. Discrimination of Alca obsidian to the subsource level using portable X-ray fluorescence represents a major advance in nondestructive provenance analysis. Further nondestructive analysis of robust sets of obsidian artifacts within Peru will allow high-resolution study of the evolution of central Andean exchange systems.