A nine-meter library of stone tools
On the eastern edge of the Serengeti plains stands Nasera, a massive, isolated rock formation, or inselberg, made of quartz-feldspathic gneiss. For over a hundred thousand years, its northern face provided shelter for early humans, and in the process, it recorded their existence. The ground beneath the overhang contains a nine-meter-deep sequence of archaeological deposits, with 25 distinct layers. This deep, continuous record allows scientists to study technological and environmental changes over an immense period of time.
Excavations at Nasera began with the famed paleoanthropologist Louis Leakey in 1932 and were significantly expanded by Michael Mehlman in the 1970s. The layers they uncovered represent a nearly continuous timeline from the Middle Stone Age (MSA) through the Later Stone Age (LSA) and into the Pastoral Neolithic period. The lowest, and oldest, layers contain MSA toolkits, characterized by techniques like the Levallois method, which produced predictable flake shapes. As excavators moved up through the layers, the toolkits changed, showing a clear technological transition.
The upper layers reveal a shift to LSA technologies. These toolkits are different, featuring an abundance of bipolar and laminar (blade) methods. The appearance of microliths—small, precisely shaped stone pieces like crescents and trapezes—marks a significant innovation. These small pieces were likely hafted onto wood or bone to create composite tools. The site also contains artifacts from the Pastoral Neolithic, including pottery, showing its long-term use by different cultures.
Innovation driven by a changing world
The deep record at Nasera catalogues tools and links the development of these technologies to major shifts in the ancient environment. Faunal remains—the bones of animals processed at the site—show a changing ecosystem. Analysis of animal bones from a Later Stone Age level dated to around 47,000 years ago shows a prevalence of species like Alcelaphini (hartebeest and wildebeest relatives), Antilopini (gazelles), and Equus quagga (plains zebra). The dominance of these animals indicates the surrounding environment was a dry, open grassland.
This evidence, combined with sediment analysis, allows researchers to reconstruct the climate at different periods of occupation. The transition from the larger, more generalized tools of the Middle Stone Age to the smaller, more specialized composite tools of the Later Stone Age corresponds with periods of environmental fluctuation. As rainfall patterns shifted and the landscape changed from more wooded to open savanna, human populations had to adapt their hunting and survival strategies. The development of new toolkits, such as those with backed microliths appearing after 46,000 years ago, reflects this adaptation. The archaeological sequence at Nasera shows that as the environment presented new challenges, human ingenuity provided new solutions.