Harappan Technology, Homo Floresiensis, Foraminifera

Some exciting readings for you- 

1)  Manufacture of synthetic stone in the Bronze Age Harappan Civilization.

Stone beads were important in Harappan culture and trade. They were made out of agate, an amorphous or cryptocrystalline form of silica. The Kutch region was the primary source of these agates. Stone and bead processing Harappan age workshops abound in this region. The tradition continues today. Some of the best ornamental agate is still being sourced from Kutch. The agates precipitate as secondary silica in cavities of the Deccan Basalts and associated silica rich lava.

To perforate these agates, the Harappans needed tools such as drill bits which were harder than the agate. For this, they manufactured a synthetic stone, now called Ernestite, by high temperature sintering of sand and laterite raw materials. Reaction temperature needed to fuse these materials into a cohesive rock would have reached 1100 deg C! Mesozoic sandstone, found all over Kutch, provided the sand, and the laterite came from iron rich weathered layers capping the Deccan Basalt.

A terrific study by M.K. Mahala and coworkers that details the provenance and fabrication of this interesting artificial stone has just been published in Nature Heritage Science. There is a lot of mineralogy and geochemistry described in the paper, but the conclusions are clearly laid out for all to understand.

2) Climate change and the decline of the Hobbit.

Why are small isolated populations of animals vulnerable to extinction?

Inbreeding, small geographic range, limited access to resources, reliance on one or few food sources, a chance catastrophic event, all may be factors making them susceptible to extirpation.

A case in point is the Hobbit or Homo floresiensis, the diminutive hominin discovered on Flores Island, Indonesia, in 2003. The archaeologic record shows it lived on the island for at least one million years. Homo floresiensis is thought to be a descendant from an early Homo species which dispersed from Africa 2 million years ago. The other famous inhabitant of the island that coexisted with the Hobbit and was its main food source is the dwarf elephant Stegodon.

A careful analysis by Michael Gagan and coworkers, published in Nature Communications Earth and Environment, using geochemistry of calcite from cave deposits show how climate change and decrease in water availability may have increased competition for resources and made life challenging for the inhabitants.

Summer rainfall began declining around 76,000 years ago with record low rainfall between 61,000 to 55,000 years ago. Both the Hobbit and Stegodon fossils become rarer during this interval and disappear by 50,000 years ago. Modern humans entered Flores Island around 46,000 years ago, and whether the Hobbit interacted with them on Flores Island is uncertain. 

3) The history of the ocean, as told by tiny beautiful fossils. 

The tiny fossils are planktonic foraminifera living suspended in the upper sunlit portion of the ocean. Their shells are made of calcium carbonate. They occur in huge numbers and have short lives. Their shells drop down and carpet the ocean floor, making them valuable archives for understanding evolution. Scientists make use of them for studying climate change too. Certain changes in the chemical composition of their shell are a function of water temperature. Tim Vernimmen has written a short piece on how foraminifera inform us about past environmental crisis and ocean conditions.

Articles: Trace Fossils, Supercontinents, Harappan Hydrology

 Some interesting geology rich readings from the past few weeks:

1) Ichnology is a branch of palaeontology that studies the traces made by organisms in soft sediment. These could be tracks and trails as animals move around on a substrate, or burrows constructed as escape structures or as dwellings, or bite marks on shells and bones. All these are indicative of behavior, which otherwise would be hard to discern from just the fossilized remains of body parts. Science writer Jeanne Timmons has written this lovely article on Ichnofossils and what they tell us about past ecology and animal behavior.

Trace fossils, the most inconspicuous bite-sized window into ancient worlds.

2) The earth has seen over its long geological history episodes of continents coming together to form a supercontinent, then breaking up and drifting apart forwhat seems an eternity, but eventually coalescing to form another giant landmass. When did this supercontinent cycle begin on earth. What are the forces that initiated and subsequently has maintained this mode of surface reconfiguration, and what are its consequences on tectonics, and the physical and chemical evolution of earth. A great review article by Ross N. Mitchell and colleagues.

The Supercontinent Cycle.

3) The rivers that sustained the Bronze Age Harappan Civilization have been the subject of lively research in recent years. Ajit Singh and colleagues have worked on the Markanda river catchment in the Sub-Himalaya dun region. Markanda joins the Ghaggar-Hakra river flowing through present day Harayana, Punjab and Rajasthan. They find that during the Mature Harappan Period (2600 B.C. to 1900 B.C.), large floods in the Himalaya foothill rivers sustained flow in downstream reaches, making  agricultural viable, even as northwestern parts of India experienced a reduction in summer monsoon strength.

Larger floods of Himalayan foothill rivers sustained flows in the Ghaggar–Hakra channel during Harappan age (behind paywall).

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. 

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.

The Theory Of The Glacial Sarasvati Has Been Given A Quiet Burial

Something significant went unnoticed and unreported amongst all the hoopla surrounding the recent paper on Harappan civilization and its link to climate change. The theory of the glacial Sarasvati got dumped. The paper does not even mention it as a possible reason for the reduced water flow in the Ghaggar. Based on its geographic description in the Rig Ved the Ghaggar has been equated with the Vedic Sarasvati river.

The glacial river theory proposed that the river Yamuna and the river Sutlej, both glacially sourced from the high Himalaya,  earlier flowed into the Ghaggar. They changed course around 2000 B.C or so to their present day channels. This switch starved the Ghaggar of water and it became a smaller ephemeral river. This theory also accepts that climate change did occur, but the main reason for the apparently sudden water shortage was the changing of course of the glacial rivers.

Until a few years ago, there just wasn't enough detailed work done on the sediment provenance (comparing characteristics of old channel sands of Ghaggar with those of present day Yamuna and Sutlej) and channel chronology of the Ghaggar system to say whether this theory was correct. But work  published in 2012 on river sediment provenance tied to a chronology and analysis of fluvial landforms have shown that the Yamuna and Sutlej did once flow into the Ghaggar but changed course to their present locations by late Pleistocene-earliest Holocene, thousands of years before the Harappan civilization. Since this work, no new data challenging these results has appeared. Scientists as evidenced by this paper appear to now accept that the Ghaggar was a monsoonal river right through the Holocene.

This result has annoyed not only geologists who had proposed the glacial river theory but also supporters of the indigenous Aryan theory. They had used the glacial river theory to time the presence of the Vedic people in the plains of Haryana and Punjab before 2000 B.C. The reasoning was that the Rig Ved describes a mighty Sarasvati flowing down from the mountains. Hence, it must have been glacially sourced and must have been the present day Ghaggar. The Aryans would have had to have been present in northwest India before the river became less mighty i.e. before 2000 B.C. This according to them destroyed the Aryan Invasion /Migration theory which proposed that the Aryans, who were a Central Asian people, entered India after the Harappan civilization disintegrated.

Where do we stand now in terms of the Aryan question in the light of the new results on the Ghaggar river?

Well, in exactly the same place as before! It was always futile to try to link the condition of the river, whether glacial or monsoonal to the question of the origin of the Aryans. The Rig Ved describes a big river. It doesn't really say that it was glacial in origin. If the Aryans had been present in the Punjab and Haryana before around 2000-1800 B.C. they would have seen a larger Ghaggar (due to a wetter climate).

At the same time, this supposed earlier presence of the Aryans in the Harappan realm does not automatically answer the question of their origins. They just as well could have represented an earlier wave of Central Asian migrants who settled in northwest India during the latter stages of the Harappan civilization. For this same reason, the indigenous Aryan theory would not have been strengthened even if the river had turned out to be glacial during Harappan times.

The geological history of the river cannot solve this riddle. A combination of archaeology, deciphering the script and genetics will be required. We await with anticipation the results of the DNA recovered from Harappa age skeletons.

In the meantime, people who tend to read too much into Rig Vedic hymns should accept that the Vedic poets who wrote (source) -

"This (Sarasvati river) has shattered mountain peaks with her fast and powerful waves, just (as easily) as one uproots the lotus-stems, let us invoke her,who strikes what is far and near, with holy hymns and prayers"..

and ..

"Whose boundless, impetuous and swift-moving flood gushes forth with a tempestuous roar"

may have been really looking at a brown colored muddy, silty, sluggish river originating in the Siwalik hills.

Put that down to poetic license!

Geochemical Data Supports Yamuna Became Tributary Of Ganga In The Pleistocene

How long has the Yamuna been flowing along its present course in the Indian plains i.e. flowing eastwards as a tributary of the Ganga?

Exploring the temporal change in provenance encoded in the late Quaternary deposits of the Ganga Plain - Shailesh Agrawala, Prasanta Sanyal, Srinivasan Balakrishnan, Jitendra K. Dash - Sedimentary Geology April 2013

Temporal analysis of Sr isotopes in soil carbonates and Sr and Nd isotopes in silicate fractions has been carried out in a sedimentary core (Kalpi core; 50 m long) raised from the southern bank of the Yamuna river, Ganga Plain, India. The aim of the study is to constrain sediment provenance through comparison with the modern Himalayan and peninsular river systems' water and bank sediments. Sr isotopic data in soil carbonates (0.71874 to 0.71410) and Sr\Nd isotopic data in silicate (0.72865 to 0.74544 and−13.9 to−17.2, respectively) vary significantly with depth and are indicative of both Himalayan and peninsular sources for sediments in the southern Ganga Plain. The positive correlation between 87Sr/86Sr ratio and 1/Sr in soil carbonate and the negative correlation between 87Sr/86Sr and εNd in silicate confirm mixing of sediments from these sources. Variations of 87Sr/86Sr ratios in soil carbonates show that at ~80 and 45 ka the Himalaya acted as the major source of sediments in the southern part of the Ganga Plain. The gradual decrease in 87Sr/86Sr ratios after 80 and 45 ka indicates change in source to peninsular India which is also supported by limited Sr and Nd isotope data in silicates. The change in sediment provenance corresponds well with the available climatic record and is suggestive of strong climatic control in sediment supply with high supply from the Himalaya during the interglacial period and peninsular sediments during glacial period.

Background:

K.S Valdiya On The Glacial Saraswati In Current Science

In the latest issue of Current Science, geologist K.S. Valdiya has written a long response to a paper   by  Giosan et.al 2012 which concluded that the Yamuna and Sutlej rivers of northwest India stopped flowing into the Ghaggar river by early Holocene. There is a companion paper by Clift et al 2012 on this topic which Valdiya does not elaborate on.

The Ghaggar floodplains formed the agricultural heartland of the Harappan civilization. This finding by Giosan et al and Clift et al if true, meant that during the Harappan civilization the Ghaggar was not a glacial fed river but a monsoon fed river, but likely a perennial one due to a wetter climatic regime in the Ghaggar catchment areas of the Siwaliks. That in turn had implications for Harappan water use and agriculture methods. This question has also fed the controversy about the origin of the Aryans and the relationship between Aryans and the Harrappan civilization, since some say that a glacial Ghaggar was the Vedic Saraswati mentioned in the Rig Ved, an ancient collection of hymns in the Sanskrit language composed perhaps around 1500 B.C. or so.

K.S. Valdiya strongly disagrees with Giosan et al's findings that Holocene climate imparted a characteristic geomorphology to large glacial rivers of this region and that their finding suggests that there was no glacial river flowing on the plains of Haryana and Punjab during mid late Holocene. Goisan et al in due course may provide a detailed reply to Valdiya's arguments. I do have several comments on the way in which K.S. Valdiya has presented his evidence.

Violence Part Of The Social Experience In Indus Civilization

Researchers Gwen Robbins Schug and Veena Mushrif Tripathy in an interview with Anthropology news have this to say about Harappan society:

It was argued that Harappa was a rare example of a peaceful, heterarchical state. The human skeletal material was never consulted to address this question. Based on our evidence for both exclusion and social differentiation in the mortuary practices at Harappa, we argue that Harappa was not entirely peaceful and social differentiation was part of life. We hope archaeologists working in this area will plan future excavations to include the peripheral areas outside the cities; excavation outside the city walls will tell us more about Indus society.

We are using the human skeletons as artifacts of the social experience. We used the concept of structural violence in our most recent work because it accounts for the clear distinctions we see in the burial practices, ritual aspects, prevalence of trauma and infection. The mortuary and bioarchaeological evidence at Harappa suggests that the social experience in South Asia was not exceptionally different from other early urban civilizations; the kinds of suffering and the patterns of violence present at Harappa suggests structural violence—unequal power, uneven access to resources, and oppression that leads to denial of basic needs and even violence.

Lest some people get too excited about the use of the words Harappa and violence in the same sentence, let it be made clear that this violence refers to interpersonal violence present in any complex society and not violence inflicted by outsiders during war.