Australia: The Land Where Time Began
Human Occupation of Northern India Spans the Toba Super-eruption about 74.000 Years Ago
For understanding the dispersal of Homo sapiens out of Africa and into Asia and Oceania, India is located at a crucial geographic crossroads. In this paper Clarkson et al. report evidence for long-term occupation by humans at the site of Dhaba in the Middle Son River Valley of Central India that spans the last about 80,000 years. A stone tool industry that has been unchanging was found at Dhaba that spanned the Toba eruption of about 74 thousand years ago (ka) (i.e., the youngest Toba Tuff (YTT) that bracketed between 79.6 ± 3.2 and 65.2 ± 3.1 ka, with the introduction of microlithic technology about 48 Ka. There is a strong resemblance between the stone tool assemblages from the African Middle Stone Age (MSA) and Arabia, and the earliest artefacts from Australia, which suggests that is the likely to be the Product of Homo sapiens as they dispersed to the east out of Africa.
According Clarkson et al. India is a focus of intense debate about the timing of arrival of Homo sapiens, the material culture signature of occupation by modern humans, the nature of the replacement of archaic populations, and the impact on populations of hominins of the YTT volcanic eruption about 74 ka. For this key period of time there is no known fossil record of hominins, analysis of DNA of contemporary populations of India indicates that the region was an important geographic stepping stone in the colonisation of Australasia by Homo sapiens (Atkinson, Gray & Drummond, 2007). The issue of whether H. sapiens arrived in India before the YTT event (dated by 40Ar/36Ar to 73.88 ± 0.32 ka1 and 75 ± 0.9 ka2) (Storey, Roberts & Saidin, 2012; Mark et al., 2014; Rose & Chesner, 1987; Acharyya & Basu, 1993; Shane, 1995; Westgate et al., 1998; Pearce et al., 2014; Pearce, Westgate et al., 2019; Petraglia et al., 2007) with a non-microlithic African MSA technology that was comprised of Levallois and point technology (Petraglia et al., 2007; Clarkson, 2014; Groucutt, 2014), or entered the subcontinent about 50-60 Ka with Howiesons Poort microlithic technology (Mellars et al., 2015), is at the heart of this debate. The reality is that though this debate is pivotal to understanding the archaeological signature of modern humans throughout the region, very few sites in India are dated to the crucial time period between 80 and 50 ka, therefore reliable evidence which could be used to test competing hypotheses is scarce. The debate over the South Asian record is focused to a large extent on stone tools and the DNA of modern populations, as well as rare finds such as the engraved ostrich eggshell and worked osseous tools from a few sites (Mellars et al., 2015), as a result of the sparse human skeletal record from the Pleistocene between Africa and South Asia (Dennell & Petraglia, 2012; Rabett, 2018).
In this article Clarkson et al. report detailed descriptions of a rich collection of lithic artefacts that have been recovered from the Dhaba locality, which is situated on the banks of the Middle Son River in Madhya Pradesh, in northern India, which is comprised of 3 nearby localities (Dhaba 1, 2, and 3) (Haslam et al., 2012) as well as the associated luminescence age estimates. A detailed archaeological sequence is provided by the Dhaba locality for the Middle Son Valley in a crucial time range of about 80–40 ka, and is positioned chronologically between the early Middle Palaeolithic/Late Acheulian sites of Patpara, Nakjhar, Khurd, Sihawal and Bamburi 1, dated to about 140 to less than 104 ka (Haslam, 2011; Shipton et al., 2013) and the blade-based technologies of the ‘Upper Palaeolithic’ that were recovered from the deposits at Baghor Formation, that had previously been dated to about 39 ka, though the latter age is problematic (Jones & Pal, 2009; Petraglia et al., 2012) (see Supplementary Discussion for more detailed discussion and Supplementary Fig. 8 for site locations). Clarkson et al. report in this study infrared stimulated luminescence (IRSL) ages for feldspar rich in potassium (K-feldspar) grains, which were collected from cultural sequences, were excavated at Dhaba. In order to frame chronological changes in lithic technology at this site and to place the evidence within the context of the South Asian Palaeolithic and, more broadly, the dispersal of modern humans (Field, Petraglia & Lahr, 2007), they used the IRSL ages.
There are 3 archaeological excavations that comprise the Dhaba locality (Dhaba 1, 2 and 3) on the northern banks of the Son River and west of its confluence with the Rehi River. The 3 archaeological excavations are each consisted of a step trench placed into hill slope sediments. Dhaba 1 (N 24o29’57.6”, E 82o00’35.0”) was selected as the location that had the densest surface artefact concentration that dated to the Middle Palaeolithic, with artefacts that were visibly eroding from the sediment at several points up the slope. Dhaba 2 (N 24o29’55.4”, E 82o00’24.5”) and Dhaba 3 (N 24o29’56.1”, E 82ooo’22.5”) were selected for excavation because of the eroding accumulations of artefacts from the Middle Palaeolithic, and a dense concentration of cryptocrystalline microblade and small flake artefacts higher up the slope at Dhaba 3. At Dhaba 1 and Dhaba 2 excavations are about 600 m and about 900 m west of the Rehi-Son River confluence, respectively. The trenches were excavated into colluvial and alluvial sediments that overlie the Proterozoic sandstone and shale bedrock of the Vindhyan Supergroup (Ray, Veizer & Davis, 2003; Korisettar, 2007). Substantial deposits of YTT, that are chemically identified, are exposed about 700 m to the east of Dhaba: at Ghogara on the northern bank of the Son River (Jones, 2010; Gatti et al., 2011), and on the east bank of the Rehi River (Lewis et al., 2012; Neudorf, Roberts & Jacobs, 2014a; Neudorf, Roberts & Jacobs, 2014b), in cliff sections.
Pedogenically altered alluvial sands, silts and clays were exposed in the step trenches. At Dhaba 1 and Dhaba 2, the top step trenches are about 16 m above the river level. At Dhaba 1 the trench revealed a sequence of floodplain silts, clays and sands with angular sandstone and shale pebbles, carbonate nodules and rhizoliths that coarsened-upwards. Angular limestone, sandstone and shale boulders that were derived from the underlying bedrock are overlain by these floodplain sediments. At Dhaba 2 the trench exposes floodplain clays, silts and sands that contain carbonate nodules and a few angular pebbles that overlie shale bedrock. At Dhaba 3, that is about 1 km west of the Rehi-Son River confluence, a trench that is about 3 m deep and about 21 m above the level of the river that was dug into the southeastern facing slope of a hill that is composed of colluvial silts, sands and gravels that overlie sandstone and shale bedrock that is decomposing. At the top of the hillock the estimated thickness of the colluvial sediments is about 5 m. Silty sands and pebble gravel, with angular sandstone and shale clasts, is exposed in the trench. South and southeast draining gullies that feed into a channel, in turn, drains into the Son River, separate the hillock from the neighbouring sandstone and shale bedrock ridge which rises to the west to more than 40 m above the river level. A terrace that dates to the Holocene that is about 10 high, that is composed of sands and silts abuts the north bank of the Son River (Haslam et al., 2012; Neudorf, Roberts & Jacobs, 2014b). Large, angular quartzite boulders, that are exposed intermittently for more than 100 m along the riverfront, is underlain by this terrace. The removal of large flakes by the use of hard hammer percussion is visible of some of these boulders, which is suggested by Clarkson et al. to possibly be for the manufacture of quartzite Acheulean cleavers that have been recovered from of the sites in the region.
Evidence of long-term occupation by humans that spanned about the last 80 ka has been provided by excavation sites at Dhaba. Occupation spans the Toba eruption and it is shown by the sandstone tool industry that there was no change in technology until microlithic technology was introduced about 48 ka. The lithic industry from Dhaba resembles strongly Middle Stone Age tool assemblages from Africa, Arabia and Australia, that is interpreted here as a product of H. sapiens as they dispersed to the east out of Africa.
At the 3 Dhaba excavations the sequence of stone artefacts spans 55 kyr, from about 80 to 25 ka, during which there are several distinct pulses in artefact discard. There are 3 major technological phases that characterise the sequence.
Dhaba 1 assemblage accumulated between about 80 and 65 ka, and is comprised of a predominantly recurrent Levallois core assemblage that includes centripetal, bidirectional, and unidirectional Levallois flakes, Levallois points, Levallois blades, notches and scrapers; these tools are made almost exclusively of chert, mudstone and silicified limestone. Also present are multiplatform and bidirectional cores, as well as redirecting flakes. Flakes show predominantly radial and weakly radial scar patterning that is consistent with centripetal reduction. There is also red ochre present in the Dhaba 1 assemblage.
Between about 55 and 47 ka Levallois technology continues to dominate the Dhaba 2 and 3 assemblages (strata k and J at Dhaba 3, and strata I to E at Dhaba 2) when the deposition of artefacts peaks. There is no Levallois technology above stratum E which was dated to 47.5 ± 2 ka. At about 48 ka microlithic technology appears in stratum D in Dhaba 2 and stratum J in Dhaba 3, with microblades, backed artefacts and unidirectional and bidirectional microblade cores that all appear in these strata.
Throughout this microlithic phase quartz is the dominant material, followed by agate. Predominantly centripetal flake scar patterning continues to be shown until the microlithic change (strata 2D and 3G and 3H), when the dominant dorsal morphology becomes proximal and bidirectional scar patterning. Artefact discard drops dramatically at Dhaba 2 and 3, and very few microlithic artefacts are recovered after this time (above strata 3C and 2D). Throughout the final period of occupation of the site agate and chalcedony are the most common materials, and mainly bidirectional and proximal flaking orientations are shown by flakes. The broad changes in the proportion of key types through time are statistically significant (Pearson chi-square = 2109; N = 864; p = 0.0005 one-sided).
A key missing component in the chronological sequence is contributed by the luminescence ages of the Dhaba locality, as well as a glimpse into the nature of technological change that took place in India between 80 and 24 ka. The sequence closely mirrors that at Jwalapuram in southern India (Clarkson, Jones & Harris, 2012; Clarkson et al., 2018; Petraglia et al., 2009), displaying a change from recurrent Levallois technology to an increasing use of single and multiplatform technology, and, then the manufacture of microlithic assemblages. In both the Middle Son and the Jerreru River valleys the technology changes appear to be stepwise, involving broad and statistically significant changes in selection of raw materials, changing strategies of retouching (from scrapers and points to backed artefacts), systematic shifts in the core reduction technology, and the introduction of new forms of retouched artefacts such as backed microliths as Levallois technology disappears (Clarkson, Jones & Harris, 2012; Clarkson et al., 2018). At Dhaba there is also some overlap between Levallois and microlithic technology that occur together in stratum J in Dhaba 3 (48.6 ± 2.7 ka) and stratum E in Dhaba 2 (47.5 ± 2.0 ka). Stratified assemblages that span the YTT event and the transition from Levallois to microlithic traditions are presented by the Dhaba sequence. In India, other key sites also represent gradual changes from the Middle Palaeolithic to the microlithic, such as Bhimbetka (Misra, 1970) and Patne (Sali, 1989), though neither of these sites has been well dated by the use of modern geochronological techniques and are not known to contain any traces of YTT.
Clarkson et al. found that the sequence offered by Dhaba is further support for the idea that MSA-like technologies were present in India prior to and following the YTT eruption (Petraglia et al., 2007; Clarkson, Jones & Harris, 2012; Blinkhorn & Petraglia, 2017). Lithic technology evolved away from Levallois towards lamella core reduction systems, and the introduction of microlithic (in the form of backed microblades) that most likely occurred long after the first appearance in the region of H. sapiens (Clarkson, Jones & Harris, 2012; Clarkson et al., 2018).
An exit of modern humans from Africa about 70 – 52 ka (Pagani et al., 2016; Kuhlwilm et al., 2016) is pointed to by recent analyses in which all non-African people branched off from the same ancestral population that left Africa, possibly with minor genetic contributions from an earlier non-human migration wave (Pagani et al., 2016; Nielsen, 2017). Earlier dispersals of modern humans is supported by fossil evidence, with modern humans present in Greece and the Levant by 200-185 ka (Harvati et al., 2019; Hershkovitz, 2018), Arabia by about 85 ka (Groucutt et al., 2018), China prior to about 80 ka (Liu et al., 2015), and Southeast Asia by 73-63 ka (Westaway et al., 2017), in association with MSA/Middle Palaeolithic technology (where stone artefacts are present). A modern presence at the eastern end of the ‘southern arc’ dispersal route by 65 ± 6 ka, which is also indicated that groups of modern humans are likely to have colonised South Asia prior to this time, is documented by recent finds from Madjedbebe in northern Australia. The strong connections between Aboriginal and South Asian modern human genomes is consistent with dispersal through South Asia (Atkinson, Gray & Drummond, 2007; Mondal et al., 2016; Rasmussen et al., 2011; Reich et al., 2011) and admixture with Denisovans somewhere along the route (Vernot & Pääbo, 2018; Jacobs et al., 2019). In northern Australia about 65 ka, the presence of centripetal and retouched point technology, make connections with Southeast Asia, India and East Africa much stronger that had been proposed previously (Clarkson, 2014; Groucutt et al., 2018). These technologies co-occur in sites east of Africa that have been dated to between 100 and 47 ka, which suggests they were likely stepping stones along the southern arc dispersal route (Clarkson, 2014). Quantitative comparisons of core technologies from along the route that point to technological continuity between Africa and Australia further support this hypothesis. According to Clarkson et al. the dispersal of modern humans out of Africa, and more importantly east of Arabia, must therefore have taken place earlier than about 65 ka, so cultural and fossil evidence from sites that date to this period will be important for future tests of this hypothesis, notwithstanding that population contractions and turnovers may have also occurred. The Dhaba locality serves as an important bridge that links regions with similar archaeology to the east and west.
Clarkson, C., et al. (2020). "Human occupation of northern India spans the Toba super-eruption ~74,000 years ago." Nature Communications 11(1): 961.
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