Identifying disturbance in archaeological sites in tropical northern Australia: Implications for previously proposed 65,000‐year continental occupation date

Abstract

The stratigraphic integrity of archaeological deposits in the seasonally wet tropics can be disrupted by termite activity and other processes. Significant questions have been raised about the surprisingly old age estimates for artefacts recovered from two sites in northern Australia: Nauwalabila and Madjedbebe. If accurate, a 65,000‐year date for the latter would represent a 30% increase in the currently accepted length of human occupation of the continent. The oldest estimate for Nauwalabila falls just short of that. These dates would have important implications for human dispersal across Eurasia in the Late Pleistocene. No other data from Australia support them. Smith et al. (2020) claim to refute the notion that termite disturbance accounts for these anomalies. Here we show that the criteria on which the assertion is based are invalid. Radiocarbon data from both sites, not cited by Smith et al. (2020), are consistent with the termite‐disturbance hypothesis. Luminescence data claimed to offer strong support for the early Madjedbebe estimate are also consistent with termite disruption. We conclude that the early dates for human presence at Madjedbebe and Nauwalabila must be rejected along with any chronometric inference about human behaviour to the degree it relies on them.

Letter to the editors on termite stone lines

“…We agree with Williams et al (2020) that soil horizons are typically poorly developed in the seasonally wet tropics. However, it is well understood (Holt & Lepage, 2000) that as termites open up the fabric of a sediment, their activity facilitates a range of physical and chemical changes in soils.…”

“…On this basis, the soil above a termiteproduced stone layer will have mineralogical or chemical properties that distinguish it. Williams et al (2020) agree that prolonged termite activity is required to form stone lines. In such cases, it is likely that direct evidence of termites-ranging from remains of galleries, fecal pellets, fragments of termite cuticle or termite corpses to clay aggregates-will be apparent in micromorphological examination of sediments.…”

“…There are no grounds for expecting that archaeological deposits will differ from other sediments in this regard or that mounds (termitaria) are the default outcome of termite activity. Williams et al (2020) estimate that it takes 10,000-15,000 years for the formation of a subsurface stone line, and that these features form at the foraging limits of termites. The corollary is that a surface (ancient or modern) must be more or less stable over a substantial period to allow a well-defined stone line to develop.…”

“…We can infer, therefore, that wherever stratigraphic details-including microlaminations-are preserved, that termite activity is unlikely to have been intensive. Williams et al (2020) dismiss several methods used by archaeologists to explore structure in their sites: analysis of spatial patterning, magnetic susceptibility, micromorphology, and analysis of conjoinstheorizing that evidence of structure is irrelevant, as downward "settling" of lithics and charcoal through a sediment mantle will preserve the original relationships between artifacts. They hypothesize that an archaeological assemblage can be translocated ("settle") through a sediment column without affecting its structure.…”

“…From first principles, we expect that size sorting of artifacts will be determined by (a) the heterogeneity of the parent assemblage-which can range from large grindstones and edge-ground axes to much smaller flaked stone artifacts and fine flaking debitage-and (b) by the time spent in passage within a profile. Williams et al (2020) hypothesize that wherever termite activity is present, an artifact assemblage will inevitably be translocated without apparent effects on its structure and will "settle through a sediment column … like a handful of gravel slowly sinking through a bucket of honey." This is unlikely except at the short scale (10-50 mm), and this hypothesis is entirely without supporting data.…”