Researchers analyzing the molecular fossils left behind by plants at a 1.8-million-year-old Olduvai Gorge site have discovered that early humans had reliable access to potable fresh water as well as the animal and plant resources that come with it. The findings are published in Proceedings of the National Academy of Sciences this week.
The availability of fresh water and plants for food and protection shapes diets and behaviors. But until now, the fossil evidence for how hominins (the group that includes us and our extinct ancestors) coexisted with these sorts of local resources was scant.
Now, a team led by Clayton Magill of ETH Zürich excavated 71 buried soil samples across a 25,000-square-meter (270,000-square-foot) area at Olduvai Gorge, and then they analyzed the biomarkers in the soil in order to distinguish between the different co-occurring plant types. Different types of plants each leave behind their own characteristic organic geochemical fossils, called biomarkers, in the soil. Trees, grasses, and other such terrestrial plants produce leaf waxes with a chemical structure that’s different than aquatic plants and phytoplankton. Additionally, plants in closed forests undergo photosynthesis differently than that of plants in open, arid-adapted grasslands, while woody and non-woody, herbaceous plants leave behind different relative abundances of compounds called phenols.
Their biomarker analyses revealed that a diversity of edible plants as well as protective woodlands were available to the hominins. Their ancient patchwork landscape was comprised of freshwater wetlands fed by a spring, which was located near woods surrounded by open grasslands. In addition to the presence of aquatic animals, there were numerous animal bones with cut marks on them located within the thicketed area – just meters away from ferns, sedges, and various wetland vegetation.
Together, the bone debris, plant biomarkers, and previously published hominin remains (adults and juveniles) define a clear spatial pattern placing animal butchery in an isolated forest patch near fresh water teeming with resources. The early humans may have brought their animal prey from nearby grasslands and wetlands over to the forested area, which likely served as a refuge to protect them from predators.
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