Tuesday, August 25, 2015

Theories Of Dispersal Of Homo Sapiens From Africa

Huw S. Groucutt and colleagues in Evolutionary Anthropology lay out the evolving story of the dispersal of Homo sapiens from Africa. The review brings together fossil, genetic  and archaeological data which now strongly leans towards a scenario of multiple migrations of Homo sapiens out of Africa beginning more  than hundred thousand years ago. These migrations followed ecological  windows of opportunity.  Interglacial phases resulted in wetter climate in the Levant and Arabia and may have made viable migration routes following either coastal contours or more interior passages towards the rest of Europe and Asia.

An Excerpt:

A variety of dispersal models (Table 1) address the period between the widely accepted African origin of Homo sapiens by around 200-150 ka and the arrival of our species at the margins of the Old World, including Australia, Siberia, and northwest Europe, by 50-40 ka.1–4 The evolutionary, demographic, and cultural processes between these milestones remain unclear, but a variety of recent studies add important new data.Whereas earlier models focused on assessing the geographical origins of our species based on fossil data, more recent approaches seek to combine fossil, genetic, archeological, and paleoenvironmental data to illuminate the nuances of dispersal into Asia (Table 1). These models emphasize different hypotheses concerning factors such as when dispersals began, how many occurred and which routes were followed. Recent models have largely fallen into two broad categories, emphasizing Marine Isotope  Stage (MIS) 5 (early onset dispersal model) or post-MIS 5 (late dispersal model) time frames (Table 1). This, however, is not a rigid dichotomy. For example, models proposing an early onset to dispersal are consistent with subsequent post-MIS 5 dispersals having also played an important role in patterns of human diversity.

The map below shows the distribution of Middle Paleolithic sites plotted on a modeled precipitation map of the last interglacial (MIS 5). The abundance of sites in the interior of Arabia speaks against a strictly coastal migration route into India. The interior of Arabia during humid phases would have been a mix of grasslands and riparian corridors offering potential dispersal routes into India and the rest of Asia.

Source: Huw S. Groucutt et. al. 2015

What is the Indian context?  The generally accepted earliest  modern Homo sapiens skeletal record in South Asia are ~35 k old fossils in Sri Lanka. But the tool record indicates presence of modern humans in India much before that. This review suggests that the totality of the tool records favors the theory that Homo sapiens may have entered India during MIS 5 more than a hundred thousand years ago, followed by additional  migrations beginning around fifty thousand years ago. Groucutt et. al. mention that future fossil discoveries from South Asia have the potential to transform ideas about the dispersal of Homo.

As of date the skeletal record of Homo in India consists of just a few fossils . Research by A.R.  Sankhyan and colleagues show that all of these have been found in the Narmada valley at Hathnora and a few km away at Netankheri . At Hathnora, hominin fossils occur in fluvial conglomerate and sand layer. One is a partially preserved calvarium and has been identified as a "robust" late Homo erectus or an archaic Homo sapien. Its cranial capacity is estimated to be 1200 cc to 1400 cc putting in the range of modern humans. It is associated with a collection of heavy duty large flake Acheulian hand axes and cleavers and chopping tools. The other fossil find at Hathnora consists of two clavicles and a partial 9th rib, interpreted to be belonging to a separate population of "short and stocky" archaic Homo sapiens associated with smaller Middle Paleolithic implements.  The cranium has been dated to the Middle Pleistocene ~ 250 k, while the clavicles and 9th rib appear to be younger with an estimated date to be ~150K range. A change in the ecology of this region is seen in the younger deposits based on the faunal content. The large flake tool industry disappears at this point in time . This has been interpreted to mean a migration of the larger robust archaic hominin away from this area based on appearance on this tool typology further north of this region and as far southeastwards to the Bastar region of Bihar.

At Netankheri, a partial femur and a humerus have been found. The femur occupies the same stratigraphic level as the Hathnora calvarium  and has been interpreted as belonging to late Homo erectus -archaic Homo sapien. The humerus though is of the "short and stocky" morphology and interpreted to represent an early modern Homo sapiens. Delicate bone implements have been found along with this fossil.  It is thought to be much younger, dated to be around 75 k, based on its stratigraphic position just below the Baneta Formation which contains Younger Toba Ash layers (ash deposits of the Toba eruption). The researchers interpret this to mean evolution from an archaic to a modern form, population continuity and continuous occupation of this area by this morphologically distinct hominin through the Middle and Late Pleistocene.

In summary, the skeletal and tool record points to presence of two culturally and physically distinct archaic hominin populations occupying the Narmada valley in the Middle Pleistocene. The tool record shows that Homo has been present in India for more than a million years and these physically distinct Middle Pleistocene hominins may be indicating the evolution of distinct hominin lineages in India. Or, was this population differentiation and morphological evolution inherited from an older African population structure, representing separate Middle Pleistocene migration episodes? And how they fit into the broader story of modern Homo sapiens dispersal and occupation of India remains to be worked out.

What is the margin of error on the 150 k date of the "short and stocky" hominin. Could they be younger and represent the early MIS 5 dispersal from Africa ( 100-125 K)?  Of interest are the ~35 K old Homo sapiens fossils from Sri Lanka which are physically distinct from the Netankheri "short and stocky" population. This points to another more recent (MIS 3) migration from Africa. Did these recent arrivals interbreed with the resident archaic hominins?  More fossils from South Asia are needed to fill in these gaps in our understanding of hominin evolution in India.  The authors of the Narmada hominins paper suggest that the "short and stocky" population may have contributed ancestry to later short bodied  populations of South Asia including the pygmies. Certainly, recent genetic work shows interbreeding between modern humans and other differentiated hominins like Neanderthals and Denisovans in Europe and East Asia respectively. Perhaps the Indian story is also one of assimilation of the earlier hominin populations with later human entrants.

Monday, August 17, 2015

Global Warming Hiatus And Internal Natural Climate Variability

This is worth sharing. A short but useful explanation of the global warming "hiatus" and the natural variability of different atmosphere-ocean phenomenon that influence global mean surface temperature (GMST) trends.

From the article-
Every decade since the 1960s has been warmer than the one before, with 2000 to 2009 by far the warmest decade on record (see the figure). However, the role of human-induced climate change has been discounted by some, owing to a markedly reduced increase in global mean surface temperature (GMST) from 1998 through 2013, known as the hiatus (1–3). The upward trend has resumed in 2014, now the warmest year on record, with 2015 temperatures on course for another record-hot year. Although Earth's climate is undoubtedly warming, weather-related and internal natural climate variability can temporarily overwhelm global warming in any given year or even decade, especially locally.

And an excerpt about the role of the Pacific Decadal Oscillation-

There is also strong decadal variability in the Pacific Ocean, part of which is the Pacific Decadal Oscillation (PDO) (see the figure, panel B). The PDO is closely related to the Interdecadal Pacific Oscillation (IPO) but has more of a Northern Hemisphere focus. Observations and models show that the PDO is a key player in the two recent hiatus periods (2). Major changes in trade-winds, sea-level pressure, sea level, rainfall, and storm locations throughout the Pacific and Pacific-rim countries extend into the southern oceans and across the Arctic into the Atlantic (7–9). The wind changes alter ocean currents, ocean convection, and overturning, for example affecting the Atlantic Meridional Overturning Circulation (10). As a result, more heat is sequestered in the deep ocean during the negative phase of the PDO (1, 6, 9, 11, 12). GMST therefore increases during the positive phase of the PDO but stagnates during its negative phase (see the figure) (13).

more here..

Wednesday, August 12, 2015

Assessment Of India Coastal Erosion

Some data points on changes in India's coastline due to erosion and accretion over 15 years (1989-91 to 2004-2006)

Assessment of coastal erosion along the Indian coast on 1 : 25,000 scale using satellite data of 1989–1991 and 2004–2006 time frames 

The  long  stretch  of  coastline  on  either  side  of the Indian  peninsula  is  subjected  to  varied  coastal  processes  and  anthropogenic  pressures,  which  makes  the coast vulnerable to erosion. There is no systematic inventory  of  shoreline  changes  occurring  along  the  entire  Indian coast  on 1:25,000  scale, which is required for  planning  measures  to  be  taken  up  for  protecting the coast at the national level. It is in this context that shoreline  change  mapping  on  1:25,000  scale  for  the entire Indian coast based on multi-date satellite data in GIS  environment  has  been  carried  out  for  1989–1991 and  2004–2006  time  frame.  The present  communication discusses  salient  observations  and  results  from  the shoreline   change inventory.   The   results   show   that 3829 km (45.5%) of the coast is under erosion, 3004 km (35.7%)  is  getting accreted, while  1581 km (18.8%)  of the coast is more or less stable in nature. Highest percentage  of  shoreline  under  erosion  is  in the Nicobar Islands (88.7), while the percentage of accreting coastline  is  highest for  Tamil  Nadu  (62.3)  and Goa  has the highest   percentage   of   stable   shoreline   (52.4).   The analysis shows that the Indian coast has lost a net area of  about  73 sq.km  during  1989-1991  and  2004–2006 time  frame.   In Tamil Nadu,   a   net  area   of  about 25.45 sq.km has increased due to accretion, while along the Nicobar Islands  about  93.95 sq. km  is  lost  due  to erosion.  The  inventory  has  been  used  to  prepare a Shoreline Change Atlas of the Indian Coast.

Background geological processes keep reshaping coastlines, but this short time frame assessment seems to have captured several anthropogenic disturbances. And one big natural event- the 2004 Indian Ocean tsunami appears to have caused considerable erosion in the Andaman and Nicobar Islands.

Monday, August 10, 2015

Understanding Aquifers For Sustainable Groundwater Management

This essay  (open access) is a timely reminder from Rajiv Sinha from IIT Kanpur on the role basic geology plays in sustainable groundwater management plans.

He gives the example of the Haryana and Punjab plains where recent decades has seen large amounts of groundwater withdrawal, so large that it can be captured by satellite borne instruments measuring  changes in the earth's gravity field.  Aquifers in this region occur mostly in bodies of sand of Pleistocene and Holocene age. These sands are remnants of river channels which have built large alluvial fans, aprons of sand and finer sediments in front of the Himalayan foothills. They form lenticular bodies surrounded by finer sediment which may not be prolific aquifers. Understanding this spatial heterogeneity of aquifers is crucial for coming up with a workable aquifer management plan.

He recommends the following -

1) Replace state boundaries with aquifer boundaries
2) Integrate all available groundwater data from the Central Groundwater Board (CGWB) and State Groundwater Boards into an integrated database for water-level characterization
3) Update the ways in which subsurface aquifer data are combined and analysed
4) Registration of all tube well locations
5) Update training for subsurface aquifer analysis and characterization

Besides basic sedimentological and stratigraphic studies to delineate aquifer boundaries, Sinha makes another extremely important  point. Data needs to be shared by institutions, and research findings made by Universities and other Research Institutes need to be translated into effective management plans by the respective State Groundwater Boards (groundwater comes under State control in India). This means a culture of strong institutional  linkages  and of transparency and openness needs to evolve. This has been India's stumbling block in the past. I have witnessed enough frustration expressed by some of my groundwater researcher friends here in the Deccan Basalts that their research has long been ignored by State Groundwater Agencies. This does remain a challenge, but hopefully new groundwater policies recommended by the Center and realized by the State Governments via their Groundwater Agencies (example: see this interview on Maharashtra Groundwater Act and for links to the Act. ) will provide new impetus for research and collaboration in understanding aquifers as a crucial component of sustainable groundwater management plans.