Hominin use of springs and wetlands: Paleoclimate and archaeological records from Olduvai Gorge (~ 1.79–1.74 Ma)

Abstract

An interdisciplinary study of the geologic and archaeological records of a 50 ky year period at the Plio-Pleistocene boundary in Olduvai Basin (Tanzania) revealed that a small groundwater-fed wetland was a consistent focus of hominin activity during periods of climate change (wet/dry cycles). Paleoenvironmental analysis of sedimentary records from 33 excavations in Lowermost Bed II (LMB II), Olduvai Gorge (3° S) revealed evidence of significant climate fluctuations that produced two and one half lake cycles between ~ 1.79 and 1.74 Ma. The region experienced wet-dry cycles in response to combined astronomical forcing effects of eccentricity (~ 100 ky cycle) and precession of the equinox (19 and 23 ky cycles). Rhythmic variability of the monsoon system produced wet periods followed by a transition into dry periods followed by a transition back into wet climate. A high-resolution study of the stratigraphy documented a groundwater-fed wetland complex (~ 1 km 2) that flourished during low lake levels (dry periods) and was drowned during high lake levels (wet periods). Stratigraphic analysis (temporal changes) of 916 artifacts from 13 excavations selected from a landscape transect across alluvial fan, spring/wetland and lake margin environments showed no notable differences in artifact type frequency and raw material type when comparing wet periods (as a group) and dry periods (as a group). However, a lateral shift of hominin activity on the landscape did occur between wet and dry periods. The Oldowan tool kit did not vary at spring sites between wet and dry periods, whereas the tool kit did vary at other lake margin sites between wet and dry periods. Both analyses suggest that climate affected the location of an activity, not type of activity. These data suggest that Oldowan hominins adapted their land-use patterns to exploit spring/wetland resources available during dry periods. A switch from wet to dry conditions likely altered surface and groundwater systems affecting food and potable water availability, forcing hominins to adjust their subsistence patterns.