Human occupation of northern India spans the Toba super-eruption ~74,000 years ago

India is located at a critical geographic crossroads for understanding the dispersal of Homo sapiens out of Africa and into Asia and Oceania. Here we report evidence for long-term human occupation, spanning the last ~80 thousand years, at the site of Dhaba in the Middle Son River Valley of Central India. An unchanging stone tool industry is found at Dhaba spanning the Toba eruption of ~74 ka (i.e., the Youngest Toba Tuff, YTT) bracketed between ages of 79.6 ± 3.2 and 65.2 ± 3.1 ka, with the introduction of microlithic technology ~48 ka. The lithic industry from Dhaba strongly resembles stone tool assemblages from the African Middle Stone Age (MSA) and Arabia, and the earliest artefacts from Australia, suggesting that it is likely the product of Homo sapiens as they dispersed eastward out of Africa.


Human occupation of northern India spans the Toba supereruption ~74,000 years ago
Clarkson et al.

Section 2: IRSL Dating
Supplementary Figure 1 | a, Typical IRSL and MET-pIRIR curves obtained for different stimulation temperature (temperatures are shown above each curve) from sample Dhaba1-OSL4. b, The dose response curves for the MET-pIRIR signals at different temperatures for sample Dhab1-OSL4. The data points were fitted using a single saturating exponential function (full lines).c, The residual doses of bleached sample (Dhab2-OSL4) plotted against the MET-pIRIR stimulation temperature. d, Dose recovery results (ratio of measured to given dose) for Dhab2-OSL4. The measured doses were corrected for residual dose shown in panel c. e, Anomalous fading rate (g-value) of the MET-pIRIR signals from samples Dhab2-OSL1 and Dhab3-OSL1 as a function of IR stimulation temperature. Error bars in all the panels represent 1 sigma uncertainty.  A water content of 7 ± 2 % was assumed for all samples, based on the measured (field) water content of each sample (shown in the brackets). b The internal dose rate for K-feldspar used in age calculation was estimated by assuming K = 13 ± 1% and Rb = 400 ± 100 ppm. c Residual doses of Dhab2-OSL3, Dhab2-OSL5, Dhab3-OSL2 and Dhab3-OSL6 were not measured, but are estimated based on the weighted mean of the residual doses measured for the other samples. d Des are estimated from the weighted mean of 6 aliquots of each sample. All the De values have been corrected for residual doses. e Age uncertainties are expressed at 1σ and include a systematic error of 2% to allow for any possible bias associated with calibration of the laboratory beta source.  Recent dates for pre-existing (Patpara) and new (Bamburi) archaeological sites 5 can now be used to update this model, alongside those presented for the first time in this paper.

Supplementary
Of great relevance to this study are the excavated localities of Patpara and Baghor, which preserve Late Acheulean to Middle Palaeolithic, and microlithic artefacts respectively. These pre-date and post-date Dhaba, dating to c.140 ka and younger at Patpara 5 and possibly terminal Pleistocene at Baghor, therefore leaving a large temporal gap in between. Other sites, which cover this gap and preserve late Middle Palaeolithic and early blade and bladelet technologies, are also highly relevant but evidence is limited 4 .
Artefacts from Patpara, in the far west of the Middle Son study area, were assigned to the Lower and Middle Palaeolithic based on the morphology of the assemblages collected from surface scatters and excavations. The range of stone artefact types found at Patpara includes scrapers of varying edge modification and retouch intensity, notched artefacts, burins, handaxes, cleavers, backed artefacts and cores, including Levallois, discoidal and blade cores. Only two backed bladelets were recovered and are said to derive from overlying deposits that contain Upper Palaeolithic artefacts 16  Artefacts from Baghor 3, manufactured on a range of high quality raw materials (e.g. chert, chalcedony, porcellanite), include blades, microblades, backed bladelets, burins and single platform bladelet cores, in addition to utilised red ochre 4,7 .
While the artefact assemblages from Patpara and Baghor provide large sample sizes and consequentially a detailed record of past technologies and behaviour, there is a very large temporal gap between these excavated sites, in the order of c.100 kyr. In the Middle Son valley, this gap is covered by several very small collections of artefacts that are from unexcavated contexts, deriving instead from eroded surface and section exposures that are either undated or indirectly dated. Archaeologically, these small collections of artefacts are intriguing and are of particular relevance to this study. They are described in detail by Jones and Pal 4 , who use evidence from initial reports 7,18,15 , new fieldwork and artefact analysis 4,21 . To summarise, these collections derive from younger Patpara formation sediments and early 16 Baghor formation deposits, represented by the Baghor coarse member, proximal to the current river (and approximately equivalent to the Baghor loess deposits located more towards the Kaimur foothills remained until now a poorly known period in the prehistory of the Middle Son.

Section 5: Cryptotephra investigation
Supplementary Note 1 A total of 32 discrete sediment samples, each weighing between 2 and 3 g, were collected at ~10 cm intervals throughout the sequence at Dhaba 1 and processed for cryptotephra analysis following the methods of Blockley et al. 22 .
Samples were treated with dilute hydrochloric acid at 10% to remove carbonates, and then wet sieved to isolate sediments within the 25 -80 µm grain size. Using the heavy liquid sodium polytungstate (SPT), the residues were further concentrated to contain only grains with a density in the 2.0 -2.