Karl W. Butzer

Radiocarbon Dating of East African Lake Levels

The fluctuations of the key East African lakes discussed are summarized in Fig. 4 which also includes the available evidence from Lake Rukwa (42) and Lake Chad (43) Exceot for Lake Victoria, all of these now lack surface outlets and are situated in much drier climates than the major lakes of the Western Rift Valley, which remain filled to their overflow levels. The apparent differendes among the fluctuations of the lakes are partly due to differendes in the nature of the evidence or the intensity of research or both, although there must also have been important local differences in the histories of the lakes Yet the consistencies are far more striking, most notably the coincidence of early Holocene high stands. Between 10,000 and 8,000 years ago, it seems that lakes in many parts of tropical Africa were greatly enlarged. Where evidence for the previous span of time is well resolved, it appears that transgressions leading to this high stand began about 12,000 years ago, and evidende from three basins (Victoria, Nakuru, and Chad) indicates a pause or minor recession just at or before 10,000 years ago. Wherever information is available for the period preceding 12,000 years ago, it can consistentlybe shown that lakes were much small-er . Several basins (Rudolf, Nakuru, and Chad) also show traces of much earlier phases of lake expansion. which are not yet well dated but which all occurred more then 20,000 years ago. The Holocene record subsequent to the maximum of 10,00 to 8,000 years ago is more complex. Three basins (Rudolf, Nakuru, and Chad) show an apparently concordant, positive oscillation at some point between 6000 and 4000 years ago, but it is uncertain how widely this episode is represented. Although many of these lakes that are now closed filled to overflowing at least once during the late Quaternary, it is evident from Fig. 4 that the periods of expansion were short-lived compared with phases of contraction to levels near those of today. This pattern may be in accord with fragmentary evidence from lower and middle Pleistocene formations, such as those of Olduvai(44)and Paninj (45), within which some relatively short-term lake expansions can be documented, but which lack evidence for any marked long-term departure from a balance of evaporation and precipitation similar to the present one Further, this pattern of brief moist pulsations, with a duration of perhaps 2000 to 5000 years, is also suggested by other late Pleistocene and Holocene sequences (based primarily on geomorphological and palynological evidence) from the Saharan area, Angola, and South Africa (46). In default of radiometric dating, such complex successions of relatively brief moist intervals provide few stratigraphic markers of broad applicability. This, together with the fact that vegetation, weathering processes, montane glaciers, lake size, lake salinity, and so forth are all likely to reflect the diverse aspects of Climatic change differently, underscores the strictures of Cooke (2) and Flint (3) against the use of pluvials and intrlvasas a basis for subdividing Quaternary time in Africa. Positive correlations between high-latitude glacial advances or maxima and intervals of high lake levels have been demonstrated or suggested for many areas of mid-latitude North America and Eurasia (47), and similar patterns have often been regarded as probable for tropical Africa as well. However, the evidence summarized above shows a notable lack of such correlations for the tropical lakes considered here. If glaciation and tropical lake levels were connected at all, then a far more complex-delayed, multiplefactor, or inverse-relationship must be sought for the late Quaternary (48). This renders the introduction of new climato-stratigraphic terms such as hypothermal and interstadial (49) of questionable value in East Africa. Further, whereas the so-called pluvial lakes of higher latitudes were probably due primarily to reduced evaporation (50), our computations for the early Holocene lakes Nakuru and Naivasha, as well as for the oscillations of Lake Rudolf and Lake Victoria in recent decades, suggest that many or most of the high tropical lake levels where associated with a modest but significant increase in precipitation.

Collapse, environment, and society.

Historical collapse of ancient states poses intriguing social-ecological questions, as well as potential applications to global change and contemporary strategies for sustainability. Five Old World case studies are developed to identify interactive inputs, triggers, and feedbacks in devolution. Collapse is multicausal and rarely abrupt. Political simplification undermines traditional structures of authority to favor militarization, whereas disintegration is preconditioned or triggered by acute stress (insecurity, environmental or economic crises, famine), with breakdown accompanied or followed by demographic decline. Undue attention to stressors risks underestimating the intricate interplay of environmental, political, and sociocultural resilience in limiting the damages of collapse or in facilitating reconstruction. The conceptual model emphasizes resilience, as well as the historical roles of leaders, elites, and ideology. However, a historical model cannot simply be applied to contemporary problems of sustainability without adjustment for cumulative information and increasing possibilities for popular participation. Between the 14th and 18th centuries, Western Europe responded to environmental crises by innovation and intensification; such modernization was decentralized, protracted, flexible, and broadly based. Much of the current alarmist literature that claims to draw from historical experience is poorly focused, simplistic, and unhelpful. It fails to appreciate that resilience and readaptation depend on identified options, improved understanding, cultural solidarity, enlightened leadership, and opportunities for participation and fresh ideas.

Ecology in the Long View: Settlement Histories, Agrosystemic Strategies, and Ecological Performance

AbstractThe recent Columbian polemic contrasted beneficial New World land use before 1492 with destructive Old World land management. Since archaeologists are uniquely equipped to document and model long-term settlement and land-use histories, there is both challenge and opportunity to empirically examine the ecological impact of particular agrosystems within long time frames. This paper examines the risk-minimization and ecological fine-tuning of the Mediterranean agrosystem, and its long-term ecological performance. The Mediterranean ecosystem is the product of millennia of co-evolution between the environment and human activities, but traditional land use has been conservative and ecologically adaptive, despite sporadic disequilibrium. The deviations from the norm pose a number of testable hypotheses for further examination, not only in the Mediterranean region but also in other areas such as the New World.

Late Cenozoic paleoclimates of the Gaap Escarpment, Kalahari margin, South Africa

Abstract The Gaap Escarpment is a dolomite cuesta demarcating the southeast margin of the Kalahari. Since Miocene-Pliocene times, thick masses of lime tufa have repeatedly accumulated at several points along this escarpment, and four regional sequences are described. These allow discrimination of six major depositional complexes, commonly characterized by basal cryoclastic breccias or coarse conglomerates that reflect frost shattering and torrential runoff, followed by sheets and lobes of tufa generated in an environment substantially wetter than today. A chronostratigraphy for the last 30,000 yr is provided by 14 C dating, with direct or indirect correlations to the Vaal River sequence. The regional stratigraphy as well as faunal dating indicate an early Pleistocene age for Australopithecus africanus at Taung. Repeated episodes of protracted cold or wetter climate or both begin in terminal Miocene times, and the last Pleistocene cold-moist interval began after 35,000 yr B.P. and ended 14,000 yr B.P. Early and late Holocene times were mainly wetter, whereas the middle Holocene was drier than today. The paleoclimatic sequence differs from that of the southern and southwestern Cape or that of East Africa, but close parallels are evident throughout the lower Vaal Basin and the southern Kalahari. The tufa cycles provide a unique, 5,000,000-yr record of climatic variation in the Kalahari.summer-rainfall belt that can be related to complex anomalies of the general atmospheric circulation.

Critical perspectives on historical collapse

Historical collapse of ancient states or civilizations has raised new awareness about its possible relevance to current issues of sustainability, in the context of global change. This Special Feature examines 12 case studies of societies under stress, of which seven suffered severe transformation. Outcomes were complex and unpredictable. Five others overcame breakdown through environmental, political, or socio-cultural resilience, which deserves as much attention as the identification of stressors. Response to environmental crises of the last millennium varied greatly according to place and time but drew from traditional knowledge to evaluate new information or experiment with increasing flexibility, even if modernization or intensification were decentralized and protracted. Longer-term diachronic experience offers insight into how societies have dealt with acute stress, a more instructive perspective for the future than is offered by apocalyptic scenarios.

Rise and Fall of Axum, Ethiopia: a Geo-Archaeological Interpretation

Civilizations represent human ecosystems amenable to systematic geo-archaeological analysis. The civilization of Axum, spanning the first millennium A.D., had its settlement core on the now-denuded, subhumid plateau of northern Ethiopia. Axum, a new city, began A.D. 100 as a ceremonial center, growing to over 10,000 people, as a prosperous emporium for international trade. Intensified land use led to mass movements in slope soils before A.D. 300, but a range of clayey stream deposits also implicates strong periodic floods and seasonally abundant moisture. The paleoclimatic ensemble suggests that stronger and more reliable spring rains allowed two crops yearly without irrigation, compared to only one with modern summer rains. Trade declined after 600 and Axum was essentially landlocked by 715. Intense land pressure and more erratic rainfall favored soil destruction and ecological degradation during the seventh and eighth centuries. Largely abandoned by 800 and pillaged by border tribes. Axum retained only symbolic significance as power shifted to the more fertile lands of humid central Ethiopia. Axum shows how the spatial and temporal variability of resources, and the interactions between a society and its resource base, can be fundamental in the analysis of historical process.

Das Klima der Schweiz von 1525-1860 und seine Bedeutung in der Geschichte von Bevolkerung und Landwirtschaft

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Darwin's Apes, Dental Apes, and the Descent of Man: Normal Science in Evolutionary Anthropology

This paper sketches successive refinements, optional renderings, and disclaimers of the ape model of hominid evolution from its initial statement by Darwin, Huxley, and Haeckel until 1973. I suggest that of the four principal ape models that have been advanced-brachiating troglodytian; brachiating, bipedal hylobatian; knuckle-walking, brachiating troglodytian; and pristine ground ape-the hylobatian model of Morton is the most convincing. Thus, future biomechanical, experimental, and theoretic studies might be profitably focused on determination of the arboreal adaptive complexes that were fundamental to the initial divergence of the hominids and the pongid apes. The 19th-century ape model and the burgeoning research provoked by it during the past century seem to satisfy Kuhns criteria for the establishment of a normal science. Hence we might refer to the ape paradigm as the foundation of a normal science of evolutionary anthropology, especially in the aspect which deals with the emergence and other early phases of the hominid career.

Lithostratigraphy of Border Cave, KwaZulu, South Africa: a Middle Stone Age sequence beginning c. 195,000 b.p.

Abstract Border Cave is well-known for its Middle Stone Age (MSA) sequence and associated hominids, as well as for the earliest demonstrable Later Stone Age (LSA) ( c. 38,000 b.p.) strata in southern Africa. Detailed lithostratigraphic and sedimentological study permits identification of 8 Pleistocene sedimentary cycles, including 6 major cold phases and 2 intervening weathering horizons. The 2 youngest cold phases are associated with the LSA and have 8 14 C dates 38,600-13,300 b.p. By gauging sedimentation rates in finer and coarser sediments, duration of sedimentary breaks, and allowing for differential compaction, the excellent radiocarbon framework provided by 28 available 14 C dates can be extrapolated to the 6 cold intervals and 2 palaeosols that are older than 50,000 b.p. These clearly span oxygenisotope stages 4, 5 and 6, placing the base of the MSA deposits at c. 195,000 b.p., Homo sapiens sapiens at c. 90,000–115,000 b.p. and the sophisticated, microlithic “Howiesons Poort” industry at 95,000 b.p. These results require radical reassessment of the age and nature of the MSA complex and of the earliest evolution of anatomically-modern people.

Late cenozoic evolution of the Cape Coast between Knysna and Cape St. Francis, South Africa

The southeastern coast of South Africas Cape Province underwent complex geomorphic evolution during the late Cenozoic, leaving a variety of erosional forms and a detailed, complementary record of distinctive sediments. The latter include several new lithostratigraphic units and paleosol horizons. An almost ubiquitous planation surface, the 200-m Coastal Platform, is associated with the fanglomeratic and deltaic Keurbooms Formation (late Tertiary?). A major sea level at +120 m truncated a laterite paleosol and was followed by accumulation of land rubble and littoral deposits to 101 m, constituting the Formosa Formation. Then follow sea level stages at +60, +30, and +15–20 m, as well as several generations of weathered eolianite, including the Brakkloof Formation with the deep superposed Brakkloof Soil. Beaches at +5–12 m, with thermophile mollusca and C 14 dates of 40,000 yr mark the Swartkops horizon, probably of Eem interglacial age. Next are cryoclastic screes and cave deposits, and ultimately the podsolic Brenton Soil of the Wurm Interpleniglacial. Transgressive eolianites and coastal dunes after 16,000 BP were interrupted by pedogenesis ca. 7500 BP and stabilized after 4200 BP when sea level reached +2.5 m. Geomorphic instability in stream valleys after 1000 BP was followed by man-induced activation of the coastal dunes, since the late 18th century. Environmental patterns accompanying this succession at various times included (1) semiarid pediplanation, (2) interior dune formation, and (3) intensive, cold-climate denudation, all under open vegetation in what is now closed, humid forest; by contrast, some of the more aberrant paleosols indicate warmer, perhumid conditions.