Tuesday, February 6, 2018

Some Thoughts On The Middle Paleolithic Stone Tools From India Story

Early Middle Palaeolithic culture in India around 385–172 ka reframes Out of Africa models - Kumar Akhilesh, Shanti Pappu, Haresh M. Rajapara, Yanni Gunnell, Anil D. Shukla and Ashok K. Singhvi

From a site in Tamil Nadu, South India, stone tool types named Levallois were dated to be 385 ka -172 ka (ka-thousand years). Levallois tools are made by striking a stone core to produce smaller flakes which are then put to various uses.  They were more versatile than the older clunkier hand axes. Previous estimates for the arrival of this technology in India was thought to be around 125 ka or later, introduced by migrating Homo sapiens.

So, who made these older Levallois tools? The recent finding from Morocco of Homo sapiens like fossils dated to be older than 300 ka has prompted many to interpret this finding as evidence of an early arrival of Homo sapiens into south Asia.

Some thoughts-

1) this discovery has put a rare spotlight on the Indian hominin record. The paucity of hominin skeletal fossils and a lack of a rigorous chronology for deposits and tools have meant that the Indian record, if not ignored, has received less attention. This study has established a robust chronological framework of the sedimentary sequence in which these tools are found. A change from older Acheulean style tools to Levallois styles is documented within this dated sequence. Finding a trend, something changing or being replaced by something else, at one locality and within one sedimentary sequence is rare at hominin sites across the world. I think this make it more a compelling story than an isolated find of some stone tools.

2) I've noticed that some media article headlines and discussions in social media are suggesting that the "Out of Africa" theory needs to be reassessed. Well, what exactly do you mean by 'Out of Africa'? The original and popular Out Of Africa theory proposes that Homo sapiens originated in Africa around 200 ka. Then, 60ka-50ka ago these modern Africans migrated and settled the globe, replacing earlier archaic human populations. But, it is not news that there have been many 'Out of Africa's'.  By that I mean there have been many dispersals of humans out of Africa. Early archaic Homo dispersals occurred by 1.8 mya. The ancestors of Neanderthals and Denisovans left Africa by 1 mya to 700 ka ago.  There is genetic, fossil and archaeological evidence for a Homo sapiens migration around 65-50 ka ago. There is also evidence of an earlier migration of Homo sapiens (dated to ~120 ka) into the Levant and possibly into south Asia as well. An older Homo sapiens fossil dated to 185 ka has been found recently in Israel. Now, this discovery of  advanced tool technology has been interpreted by some to indicate an even earlier migration of Homo sapiens into India.

To me, the bigger evolving story is that Homo sapiens are getting older and older, originating earlier that 385 ka! That they might have dispersed into Asia soon after is less of a surprise. Migrations out of Africa seem to have occurred again and again, and so another at around 385 ka doesn't seem to be an extraordinary event. There would have been back migrations into Africa as well. I suspect that the recent finding of anatomically modern humans in Morocco dated to more than 300 ka has shaped the media narrative of this stone tool finding into an 'early migration into India' story.

How would have these stone tools been interpreted without supportive fossil evidence that Homo sapiens existing by 385 ka?  There always was an alternative hypothesis that proposed that evolution of complex behavior and associated advances in tool technology took place independently in disparate human populations residing in Africa, Europe and Asia.  Aspects of 'modern' anatomy and behavior might have developed multiple times in different places.  In this context, the hominin skull dated to around 236 ka found in the Narmada valley, Central India, is intriguing. Given its antiquity, the reasonable interpretation is that it represents a population descended from an earlier Homo erectus migration into India. Yet, it has a mix of archaic and derived (modern) features. It's estimated cranial capacity is comparable to modern humans.  Is it an example of  parallel evolution of 'modern' traits outside Africa?  Or, does it represent a hybrid population formed by the mixing of archaic hominins and Homo sapiens?

Skeptics like Michael Petraglia have pointed out that the technological transition seen in India may be a local invention of technology and not due to migration of a new population carrying advanced tools. Changing environmental conditions may have spurred similar inventions in different parts of the world.

3) One point to note is whether these earlier archaics and Homo sapiens living outside Africa contributed ancestry to today's people. Some recent genetic analyses suggests that all non-Africans are descended from Homo sapiens that dispersed from Africa around 80 ka -50 ka ago. These people did mix with archaic hominins in Europe and Asia but the degree of admixture is low. We contain about 2-4% Neanderthal and/or Denisovan genes.  If this is true, if earlier people migrating from Africa did not leave much of a genetic legacy in us, then the original 'Out of Africa' model still has some relevance.

Monday, February 5, 2018

Article: Groundwater Worries In Maharashtra

Pune based groundwater researchers Dhaval Joshi and Uma Aslekar write about the need to understand the geology of aquifers and the importance of governance in managing this resource:

Understanding the Triggers of Groundwater Competition in Maharashtra

an excerpt-

The recent vagaries of rainfall and the resultant water scarcity and drought-like situation in Maharashtra has resulted in a series of supply-side programmes being implemented across the state. Be it the promotion of farm ponds or dug-wells through various government programmes, the approach has largely been supply-side interventions. The assumption behind this seems that increasing the number of sources would help resolve the crisis around water. There is a misplaced judgment when it comes to making such assumptions. One, it is perceived, even today, that it is the question of access, and that many of the users still do not have any access to any water source, be it in the form of dug-well and bore-well. etc. Second, it also justifies the understanding that users are efficient in their use of water resources, and that limited supply in itself, is a problem. These two points fuel the approach of supply-side interventions.

They identify these focus areas:

1) Granularity of data
2) Integrating hydrogeological in water security programmes
3) Need for stakeholder participation
4) Effective implementations of legislation on groundwater
5) Larger role for groundwater institutions

Open Access

Tuesday, January 30, 2018

Field Photos: Dikes At Korlai, India West Coast

Sharing a few pics of dikes intruding the Deccan Volcanics at Korlai, a small village south of Mumbai. I had taken a group of nature lovers and science enthusiasts on a traverse from Pune to the   west coast last weekend. We stopped at the Western Ghat escarpment to take in majestic views of massive lava flows and then went to the coast to observe dikes and silica geodes.

Several dikes are exposed along the rocky coastline. Most of them are oriented in a N-S to  NNW-SSE direction.

Here is one with a shape of a serpent

A close up of a dike. Notice the clear contact between the dark colored dike and the brown/grey looking basalt lava flow.

Another large dike with closely spaced fractures.

And this one, intruded along en echelon fractures, showing a sinistral or left handed offset.

A view of the rocky wave cut platform from top of Korlai fort. Arrows point to two dikes.

One interesting feature of these dikes is that many of them contain tiny fragments (2 -20 cm in diameter) of the lower crust, incorporated by the basaltic magma as it ascended. These fragments or 'xenoliths' are composed of granulite, a common rock type formed in the high temperature - high pressure environments of the lower crust. Work done by A.G Dessai and colleagues  suggest that these granulites are present at depths ranging from 15 km to 40 km below the surface. Dike chemistry suggests that the original composition of the parent basaltic magma, formed at even greater depths in the uppermost parts of the mantle, was modified  due to reaction with and assimilation of this lower crustal granulite.

That was a point of great interest to the people who participated in this field trip. They were awestruck that they were looking at solidified sheets of magma that extended to depths of more than 40 km below the surface.

Sunday, January 21, 2018

5700 Year High Resolution Record Of Indian Monsoon From Uttarakhand Cave Deposit

..continuing on the topic of environmental changes and Harappan Civilization. Gayatri Kathayat and colleagues have teased out an intra-decadal record of variability of Indian monsoons from a cave deposit in Uttarakhand.  This they did by measuring the O18/O16 ratio in the mineral calcite (CaCO3) which grew incrementally to form a speleothem. The lighter isotope of oxygen is preferentially retained in the vapour phase. Less and more amounts of rainfall thus results in less or more amounts of O16 in rain and groundwater and eventually in the mineral calcite that precipitates from that groundwater. This is known as the amount effect. A chronology of speleothem growth was established using thorium 230 dating method.

The record for the past 5700 years is summarized in this figure. The time period of the growth and consolidation of urban Harappan society coincides with a period of accentuated monsoons.

Gayatri Kathayat et. al. 2017: The Indian monsoon variability and civilization changes in the Indian subcontinent

Here is their conclusion:

The hydroclimate conditions during the evolution and subsequent decline of the IVC have remained a subject of debate (for example, 9, 14–19). On the basis of the Sahiya d18Orecord, the Early and Mature Phases occurred during a fairly wet/warm and climatically stable period. The Mature Phase began around an abrupt intensification of the ISM at ~4550 yr BP (Fig. 3) and sustained for nearly ~700 years to ~3850 yr BP, corresponding with the late portion of the mid-Holocene Climate Optimum, during which the ISM reached its maximum over the past 5700 years. It is plausible that the optimum (warm/wet) climate might have allowed the civilization to develop a farming system with large and reliant agricultural surpluses, which in turn supports the development of cities.

Previous studies have attributed societal collapses in the Middle East and in the Indus Valley to a climate event, the so-called “4.2 ka BP event” (or ca. ~4.2–3.9 ka BP event) (15–21, 42–45). The 4.2 ka BP event in the Sahiya d18O record manifests as an interval of declining ISM strength, marked by a relatively higher-amplitude d18O variability and a slow speleothem growth rate, rather than as a singular prominent abrupt event (Fig. 2). A lack of an abrupt change in our record around the time is consistentwith the idea that the 4.2 ka event did not influence the Deurbanization Phase (14) in contrast to the more severe societal impact it had on the Old Kingdom in Egypt and the Akkadian Empire in Mesopotamia (42–45). 

Some commentators have already pointed out that this sample is well removed from the Harappan realm and we need to understand regional variation in monsoons before drawing any firm link between monsoon variability and Harappan civilization phases. In that context, let me put up another figure from a study of the Kotla Dahar lake sediments from Haryana. This site falls within the Harappan region. Yama Dixit and colleagues measured oxgyen isotopes of carbonate lake sediment as well as from gastropod (snail) shells. Take a look at the figure below.

Source: Yama Dixit et.al. 2014: Abrupt weakening of the summer monsoon in northwest India ~4100 yr ago

The variation in oxygen isotope ratios is due to variation in intensity of evaporation. Greater evaporation during dry phases results in the lake water getting enriched in the heavier isotope (the lighter isotope goes into the vapor phase more readily). Sediment and shells precipitated from this water will therefore get enriched in the heavier isotope during dry phases. Their sampling is coarser than the Sahiya study. But, if you look at the time period from around 5000 BP to around 3800 BP, there is no clear persistent trend towards monsoon intensification (should show up as a centuries long shift towards more negative dO18 values since evaporation will be less during wet phases). A fine resolution local record is needed to fill in the details and explain this apparent contradiction.

Finally, I came across a talk by archaeologist Shereen Ratnagar on environmental changes, river history and the Harappan Civilization. She does not like the theory that climate change was responsible for the decline of the Harappan Civilization. Instead, she prefers a social sciences approach, arguing that factors like the over-extension of empire and social dynamics need to be taken into account. Well, I am not sure that these are mutually exclusive. Civilizations may be in a phase of political and social cohesiveness whereby they could prove resilient against environmental changes. In times where their capacity for collective action is weak for internal reasons of polity and demography, exogenous factors like climate change may trigger disruption and decline.

She spends a lot of time criticizing a study by Liviu Giosan and colleagues on the fluvial history of that region. That paper showed that during Harappan times there were no glacial rivers flowing in the region between Yamuna and the Indus. Ratnagar points out that there might have been tributaries of the Yamuna and overspill of the Sutlej that may have provided water to the channel of the Ghaggar river and so there was no severe water shortage. But Giosan's work has not claimed that! They too point out that higher rainfall in the Siwaliks would have kept the Ghaggar perennial through most of the urban Harappan phase. They find that sedimentation continued through the late Harappan phase as well. The study suggests that continued monsoon decline and drying resulted in migration away from the Ghaggar-Hakra belt. However, they don't argue for a direct link between abrupt climate change and civilization decline across the entire Harappan extent. Anyways, the talk is worth listening too, especially her analysis of the wonderful water management strategies at the Harappan age site of Dholavira in Kutch, Gujarat.

Here is the link to the video

Tuesday, January 9, 2018

Note On The Sutlej Paleochannels

The topographic relief rendition posted below shows beautifully the incised valleys of the glacially sourced Yamuna and Sutlej rivers. This rendition has been derived from the NASA Shuttle Radar Topography Mission (SRTMv3) DEM (Digital Elevation Model) with a 1 arc-second or 30m spatial resolution. The region depicted in the figure is immediately west of the Himalaya frontal ranges covering parts of Punjab and Haryana.

Source: Ajit Singh et. al. 2017 - Counter-intuitive influence of Himalayan river morphodynamics on Indus Civilisation urban settlements.

This incision began during the early Holocene, beginning about 10,000 to 8700 years ago and continuing over the next few thousand years, as proposed in an earlier study by Liviu Giosan and colleagues. A decline in monsoon strength over northwest India resulted in low sediment load carried by the rivers. Under such conditions, starved of sediment, the river starts cutting down or incising into its older deposits. Over time they carve out large valleys as the Yamuna and Sutlej have.

During the mid Holocene, from about 6000 years to 3800 years ago, the region between the Yamuna and the Indus was extensively settled and farmed by the Harappan people. The river Ghaggar flows through this region. One popular theory supported by many geologists was that during Harappan times the river Sutlej flowed into the river Ghaggar, switching to its present course only about 4000 years ago. However, Giosan and colleagues had argued that had that been the case, a large incised valley should have been carved by the Sutlej from the point it exits the Himalaya to the point it joins the Ghaggar. The absence of a wide NE-SW oriented incised valley in the interfluve between the Yamuna and the Indus indicates that the Sutlej did not flow into the Ghaggar during most of the Holocene.

 A recent study led by geologist Sanjeev Gupta (Ajit Singh et. al. 2017)  has validated this scenario using geochemical criteria. They have shown that the Sutlej river once did flow into the Ghaggar but changed course and joined the Indus in the late Pleistocene -early Holocene between 15000- 12,000 years and 8000 years ago. Additional data from Giosan and colleagues shows (SI Text) fluvial deposits of Late Pleistocene-Early Holocene age (latest being 10,000 years old) along the present day Sutlej floodplain. These staggered dates imply that a major channel of the Sutlej avulsed or changed course as early as 15000 to 12000 years ago. A smaller strand of the river continued to flow into the Ghaggar until about 8000 years ago or so.

All this means that the Harappan settlements and agriculture in this region was not sustained by a large perennial glacial fed river. Rather, the Harappans adapted their water usage strategy and farming practices to exploit a smaller and maybe an ephemeral river and more distributed water sources.

The geochemical  work by Gupta and colleagues has been rightly praised and highlighted in many media reports. What did go unnoticed and unappreciated was the relief rendition of the incised channels. They provide a very powerful visual representation of the Holocene fluvial history of this region.

The modified relief rendition below also shows the course of the abandoned Sutlej incised valley. Note that this valley is much narrower than the Sutlej and Yamuna incised valleys. Also, trace these narrower incised valleys upstream and you can see that they originate in the Siwaliks. There are no deep extensive incised valleys along the route I have marked in blue. The Sutlej would have carved a prominent incised valley roughly along the blue route had it been flowing into the Ghaggar during most of the early and mid Holocene. Its absence suggests to me that the valley annotated as the abandoned Sutlej incised valley was really carved out in the earlier part of the Holocene by the smaller Ghaggar river originating in the Siwaliks.

Modified from :  Ajit Singh et. al. 2017 - Counter-intuitive influence of Himalayan river morphodynamics on Indus Civilisation urban settlements

Aside: After Liviu Giosan's paper came out, the archaeologist Shereen Ratnagar asked me whether incised valleys are diagnostic of glacial rivers. She was puzzled because the monsoonal rivers Marakand, Ghaggar and a number of smaller streams which originate in the Siwaliks have also carved incised valleys. The answer is no, they are not. What Giosan's work was pointing out was that wide incised valleys of a particular telltale orientation were absent, thus providing a clue as to when the Sutlej changed its course.