Dating cave sediments
The cave system comprises several kilometres of mapped passageways (Figure 1a) that are stratigraphically bound to a 20–30 m-thick, chert-poor dolomite horizon capped by a 1–1.3 m-thick chert unit that forms the roof to the cave system (Dirks et al., 2015).
The fossils occur as a dense bone accumulation in mostly unconsolidated muddy sediment that largely originated from within the cave through weathering of the dolomite host rock (Dirks et al., 2015). In this paper we present results of uranium-thorium (U-Th) disequilibrium, electron spin resonance (ESR), radiocarbon, and optically stimulated luminescence (OSL) dating in combination with palaeomagnetic analyses, to provide ages for the fossils and surrounding deposits in the Dinaledi Chamber, and build upon the geological context described in Dirks et al. Dates acquired via U-Th and ESR techniques were obtained using a double blind approach for each technique to ensure robust, reproducible results, with each laboratory using their own analytical and computational approach.The results challenge our ability to associate given hominin species to specific cultures and behaviours in the past. In contrast to all other hominin deposits in the Co H, the deposits that host H.These issues are discussed in greater detail in an accompanying paper (Berger et al., 2017). naledi in Rising Star Cave are composed of largely unconsolidated, mud-clast breccia in a mud matrix with no evidence of coarse clastic sediment being carried in by water flow.This result has been confirmed independently by dating three H.naledi teeth with combined U-series and electron spin resonance (US-ESR) dating.The main cavity forming the Dinaledi Chamber is ~15 m long with variable widths not exceeding 2.5 meters (Figure 1b), and expands near the intersection with a crosscutting passage, which is the location of the main excavation site to date (Figure 1b).
There is no evidence that the present entrance into the Dinaledi Chamber has significantly changed since the deposition of the fossil hominins, with sediment accumulating mostly near the current access point (Dirks et al., 2015, Dirks et al., 2016a; Figure 2).
Importantly, the most crucial tests were carried out at independent laboratories around the world, and the scientists conducted the tests without knowing the results of the other laboratories. took these extra steps to make sure that the results obtained were reproducible and unbiased.
The estimated dates are much more recent than many had predicted, and mean that H.
By combining the US-ESR maximum age estimate obtained from the teeth, with the U-Th age for the oldest flowstone overlying Homo naledi fossils, we have constrained the depositional age of Homo naledi to a period between 236 ka and 335 ka.
These age results demonstrate that a morphologically primitive hominin, Homo naledi, survived into the later parts of the Pleistocene in Africa, and indicate a much younger age for the Homo naledi fossils than have previously been hypothesized based on their morphology.
Approaches taken by each laboratory that contributed to this paper are described in detail in the methodology section. naledi and early Homo) and associated mammals, reptiles, and birds (e.g., Vrba, 1975, 1995; Brain, 1993; Tobias, 2000; Berger et al., 2010, 2015).