Tuesday, December 22, 2015

Field Photos- Jaisalmer: Landscapes, History, Geology, Fossils

Jaisalmer was fun!

I was staying last weekend at the pretty amazing Suryagarh hotel. It is a relatively new hotel, but built in the style of an ancient fort. The interiors are stylishly crafted, with courtyards and sunlight corridors, and absolutely beautiful elegant use of lights in the evenings...the service was impeccable and the food was great too! I sampled quite a variety of cuisines, from the classic Halwai breakfast made in the Rajasthani style, to a lunch inspired by a hodge podge of different styles from Mediterranean to Thai, to another Rajasthani style meat and rice platter dinner. The highlight for me among the myriad dishes was a palate freshener made from basil, sweet melon (Mosumbi), lime and salt. It was liquid citrus basil chutney, served chilled. Simple, yet sublime!

Pune is green and black. Trees and that volcanic beast, the Deccan Basalts, give it those hues. Jaisalmer is buff, off-white, yellow, fawn, brown, rust, red, black. These are the colors of the clays and sandstones and limestones deposited in an immense sea which covered the area from the Jurassic to the early Cenozoic. I got to see only the Jurassic section, and that too only in a hurry.

Suryagarh had organized a long drive in the outback.. I guess that's the word that comes to my mind when facing an immense desert. The Thar stretches in all directions of Jaisalmer and a couple of km off-road you begin to sense the isolation.

An Oasis with the vast Thar behind.


We visited the smallish Khaba fort. The interesting history is at the base of the fort.


These are the ruins of the Paliwal community which is said to have moved to this area from Pali, Rajasthan few hundred years ago. They built a successful sustainable agricultural society, making clever use of the limited amount of available water. Then legend has it, they fell out of favor with some powerful locals and almost overnight abandoned their homes, migrating to several larger towns in Rajasthan.


All around, the Jurassic is inescapable. These are north tilted shales and sandstones. Only a few hundred feet of strata outcrop (on the surface), but there is more than five thousand meters of sediment in the Jaisalmer basin subsurface. Some layers are oil and natural gas reservoirs which ONGC has tapped into.


The shales, sandstones and limestones are fossil rich. I could spot ammonoids, belemnites and clams. In an isolated homestead belonging to a Bhil tribal family, we met this amazing old woman who scours the countryside for fossils and then sells them in the Jaisalmer market. This is her treasure trove!


.. and the Bhil family in their abode. The Bhils occupy a proud place in Rajasthan history, being most well known for the military support they gave to Maharana Pratap is his battles against the Mughal emperor Akbar. They, as most of the tribal societies in India are, quite marginalized, sustaining themselves on small farm plots and as day laborers.


Another type of remains of this ancient Jurassic life are ichnofossils. These are tracks and trails and burrows of worms and other creatures disturbing the sea floor and preserved as impressions and casts and molds. Here is a horizontal burrow system likely made by a polychaete worm like creature. The ichnofossils of the Jaisalmer area and their paleo-ecology have been well studied by paleontologists from Pune. Check out this paper co-authored by my friend P.K Sarkar from Fergusson College, Pune.

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More aspects of the geology and the physical processes prevailing in the Jurassic seas are seen in the building stones.

Here is a shell hash with pebbles, a concentration of coarse shells of molluscs and rock fragments, deposited on a Jurassic beach or in very shallow seas where strong wave action removes the finer clay and mud particles, leaving behind a lag of clean sand. Such coarse sands are of great importance to geologists. They are often quite porous and may end up hosting petroleum. So, the basic processes that control their distribution in ancient seas are studied intensely by sedimentologists.


And this great example of deposition in a Jurassic storm. The coarser pebbly layer contains "intraclasts" which are pieces of hardened sea floor that has been ripped up by storm waves, transported and then re-deposited. I could have stood and photographed the walls of the Suryagarh hotel all day. There is so much sedimentology to be learned, all literally written in stone.


The main source of water for these remote communities are these depressions where scanty rainfall accumulates. These make for a really soothing sight in the midst of the harsher surroundings.


Groundwater is usually found at depths of few hundred feet and is often saline. Aquifers are present in the top sand, as well as the Cenozoic, Cretaceous and Jurassic strata underneath. Back in the early Holocene some 8-10 thousand years ago, Rajasthan and Jaisalmer got a lot more  rain. Groundwater got stored in these deeper strata, but over the past few thousand years, the climate became drier, and these deep aquifers don't get replenished too often. Prolonged reaction of the water with the rock increases the salinity of the water.  But there are at places shallower lenses of fresh water which do get replenished from time to time. This community got lucky and has struck potable water at twenty odd feet. Here I am at one of the wells.


Another place of historical interest we visited was an ancient cemetery. Jaisalmer had trading links with Eurasia from medieval times and scattered through the countryside are tombs for the fallen traveler and important locals.


.. and off course a trip to the desert without sand dunes?.. This is part of the Sam Sand Dune National Park..


Overall, my visit was far too short, there is just a lot of history and geology to see around Jaisalmer. I did not even have the time to visit the world famous Jaisalmer fort, which is a UNESCO heritage site.  

Hey,  I am not really complaining! Who would, if you woke up to a view like this?


Wednesday, December 9, 2015

Jurassic Geology- Traveling To Jaisalmer, Rajasthan

I'm traveling to the desert town of Jaisalmer in Rajasthan state this weekend. In college, my final year B.Sc. field trip went to Rajasthan.  I suffered acute appendicitis a day before our departure and missed the trip. Then some years ago, while driving from Ladakh  to Pune, I  drove through the towns of Jaipur and Udaipur but didn't spend any time there. This is going to be third  time lucky I hope. Jaisalmer is an ancient fort town and I'll  be staying at Suryagarh, a beautiful boutique hotel. I will be getting to see the fort and some other  sights and catch some of the geology too.

It is Jurassic outcrops all around the town. Jaisalmer basin is one of the important sedimentary basins of India,  with ONGC producing oil and natural gas from Mesozoic and Cenozoic reservoirs. So,  its geology is well studied.

Here is a map of the Jaisalmer basin and the larger regional context. 


 Modified from Source: N.P. Singh 2006

This basin is the south eastermost part of the Indus shelf, which made up the sea facing continental shelf of the Gondwana/ Indian plate. I  have  outlined  with dotted brown lines the depositional orientation of the sedimentary sequence. The ancient shoreline  was to the southeast  oriented roughly NE-SW.  The strata dip (tilt) towards the north-northwest. So, one finds younger and younger rocks towards the north-northwest. A few hundred feet of sediments outcrop. The rest of the sedimentary sequence which is greater than 5000 m is in the subsurface. The map also shows the major structural elements affecting the basin. These are mainly NW-SE oriented faults along which there has been block movements. The Barmer rift is a northward continuation of the Cambay trough, a linear depression that formed in the late Cretaceous-Paleocene as India broke away from Seychelles.

These are the orientations of the basin and its structures today. I like to take a step back and understand the paleo-geography. The reason is plate-tectonics.  How was India  and this basin oriented during the Jurassic? How has plate tectonics reorganized the configuration of the continents since? One gets a better understanding of the basin history and structural evolution taking this long view.

Below is a series of paleo-geographic recontructions of Gondwana and the Indian block since the late Jurassic taken from Sanker Chatterjee et al. 2013.

Fig 1 is the late Jurassic. The sea (Neo-Tethys) flooded the continents from the north. The Mesozoic, especially Jurassic onward, was a time of high sea levels with many continents experiencing marine incursions and the formation of thick sedimentary sequences. This high sea level (with smaller intermittent sea-level drops) persisted for tens of millions of years.  One  reason was that the position of the continents during this time was such that there were no continental land masses at the poles and thus there was no build up of continental ice sheets which could have caused a large global sea level drop as did happen during the Pleistocene ice ages for example. Another reason was that Pangea from early Jurassic and Gondwanaland from later Jurassic started breaking up. Continental break up eventually leads to the formation of new oceanic crust along volcanic ridges that form along the old lines  of continental separation. This new crust being hot and buoyant forms high mountain chains rising above the sea floor. This displaces sea water which floods the continents. This process was stronger beginning latest Jurassic and through the Cretaceous, accounting for the Cretaceous high seas.


Anyways, coming back to the plate tectonic fate of India. When Jurassic sediments were being deposited, Jaisalmer was located around 25 deg south of the equator and India was oriented almost E-W.  India  then separated from Africa around 165 million years ago and drifted along with Australia and Antarctic further southeastwards! The original orientation of the ancient Jurassic shoreline was then roughly E-W which I have depicted as a brown dotted line. As you can see Jurassic sea level rise deposited sediments in a wide arc covering Madagascar as well, which at that time was attached to India.

Fig 2. By early Cretaceous, India broke away from Australia and Antarctic and starts to get pulled northwards and also rotated counterclockwise. Jurassic shoreline is shown as brown dotted line.


Fig 3. Late Cretaceous. Sea floor spreading in the Indian Ocean and the Atlantic too. India now appears to be oriented more like it is today, although its axis is still slightly N-NE. It has separated from Madagascar around 90 million years ago and with Seychelles around 65 million years ago. This latter wrenching apart has formed the extentional faults and linear depressions (red dotted line)  that cut across the Rajasthan basin in a NW-SE direction including the N-S oriented southern Cambay depression. Southwards in the state of Maharashtra, the wrenching apart of India from Seychelles triggered a massive outpouring of magma (see my previous post), resulting in the Deccan Volcanic Province. Jurassic shoreline is brown dotted line.

 
Fig 4. Eocene- Sedimentation continues on the Rajasthan shelf through the Cretaceous and Early Cenozoic. Ultimately the fate of the basin and the larger Indus shelf is sealed. India crashes into Asia. The Neo-Tethys narrows and closes and the sea disappears. Sediments eroding from the rising orogenic Sind-Baluchistan mountains fill up the Indus depression. Deep below though in the sediment pile, organic matter was being cooked into oil and natural gas, a resource that ONGC is today exploiting. Jurassic shoreline is brown dotted line.


There is a further history of the formation  of the Thar desert but I'll leave that for another time.

Check out this Suryagargh hotel I'm staying in. Its looks awesome.



 Picture source: Photo Gallery Suryagarh

Pics later after my trip.  And this was a very broad geology overview. I'll write in more details of the nature of the sediments and fossils next week!

Monday, December 7, 2015

Grand Theft Geology- Report Indicts Reliance Of Pilfering Gas From ONGC Reservoir

Paranjoy Guha Thakurta explains in a detailed article the shenanigans and the disputes over the exploitation of natural gas in the Krishna Godavari basin.

The Krishna-Godavari basin offshore Bay of Bengal composed of Late Mesozoic to Cenozoic deltaic-marine sequences has rich natural gas reservoirs  . Reliance Industries as well as the public sector ONGC are exploring and producing natural gas from adjoining areas. Turns out that in one area the underlying reservoirs are continuous, and ONGC suspected a couple of years ago that Reliance Industries realizing this geological situation drilled wells very close to the common boundary of the blocks. As a result of producing these wells as much as 11 billion cubic meters (bcm) of gas has flowed from the reservoir under ONGC controlled areas into Reliance control. Out of that, Reliance in an unauthorized manner, has sucked out 8.9 bcm of gas worth about Rs 11,000 crore  (~ $1.7 billion).

If fact, the large migration of gas from ONGC controlled reservoir into Reliance controlled reservoir means that it would no longer be economically viable for ONGC  to develop this particular field.

That is the finding of an independent consultant DeGolyer and MacNaughton (D&M) based out of Dallas, Texas, in the US, which was hired to submit a technical report on the ONGC claim which Reliance had disputed.

ONGC has also taken the Government of India to court, naming the Ministry of Petroleum and Natural Gas (MoPNG) and the Directorate-General of Hydrocarbons (DGH) as respondents accusing these agencies of failing to be vigilant in taking precautionary measures.

ONGC claimed in its writ petition:

Pertinently, four wells have been drilled by Respondent No 3 (RIL) within distances ranging within 50 m (metres) to about 350 m from the blocks of (the) petitioner (ONGC) and wells have been so drilled and constructed that there is a pre-planned and calculated slant/angular incline towards the gas reserves of (the) petitioner with a clear idea to tap the same.

According to ONGC, its nomination block, Godavari PML (G4) and discovery block, KG-D5 under the New Exploration Licensing Policy (NELP)-1 are contiguous to the RIL-operated NELP-1 block KG-D6. The public sector undertaking (PSU) had said that it wanted a “truly independent” agency to examine its contention that the Mukesh Ambani-led RIL may have drawn natural gas worth up to Rs 30,000 crore from ONGC’s fields adjacent to the ones in the KG-D6 block where the contracting company controlled by RIL operates.


all this does not reflect well on a government eager to invite foreign investments and collaboration-

Sarma is correctly of the view that management and enforcement of contracts are crucial to good governance in any sector, including the oil and gas exploration industry where the natural resources extracted are not just high in value and also critical to the country’s energy security. A flawed and inadequate PSC between RIL and the MoPNG has been greatly responsible for many of the problems that have been encountered during the exploration and extraction of gas from the KG basin. In the case of alleged theft, the management committee, which included representatives of the ministry, apparently acquiesced in whatever RIL did, and the contractual provisions for joint-management of the gas fields and imposition of penalties were never invoked. This, Sarma points out, does not augur well for a country that is aggressive inviting foreign investments, including investments in the oil and gas industry.

It should also be noted that government-owned companies like ONGC are expected to function independently and safeguard the interests of the shareholders, which include the people of India. The two really “independent” former directors of ONGC persuaded the corporation to approach the Delhi High Court but the ministry under Moily tried to prevent this from happening—it is truly ironic that the government as the major shareholder of ONGC should actively work against its interests and try and cause harm to itself.

The entire article is worth reading.

.. and more on the troubled involvement of Reliance Industries with natural gas exploitation in the Krishna Godavari basin .

Tuesday, December 1, 2015

India And Climate Change- Productivity Challenge

This is a serious essay. But this passage made me laugh out loud-

Because any imaginable path of development involves making massive amounts of steel, ramping up production at Jharia is a top national priority. Achieving Modi’s billion-ton target, company officials tell me, will require the colliery to increase its output by about 15 percent a year.

The men and women who must accomplish this huge task work in a landscaped headquarters that during my visits is full of people standing around in hallways and lobbies without obvious purpose. One morning I interview an able young engineer. Jammed into the other half of his office are a half dozen older men, one of them his supervisor, drinking tea and telling stories. The interview lasts nearly two hours. During that time the other men do not move. Phones do not ring. Email alerts do not ping. Keyboards lie untouched. The office door opens only to admit flunkies with tea on a tray. Leaving the engineer’s office, I wonder if the activists who protest India’s coal expansion plans would be comforted by this scene. Increasing productivity is going to be no easy task.


Charles Mann writes about the two paths- one solar and the other coal- that India seeks to take to develop and at the same time manage its carbon emissions. The preferred pathway according to Charles Mann's assessment is tilting towards coal.

I  kinda agree. The current government is coming up with innovative ways to speedily access India's coal deposits. One aspect of the damage by the increasing reliance on coal that he did not bring up (besides air pollution) is the destruction of some of India's best forest land in the eastern part of the country. Environmental parameters that are used  to define inviolate forest areas are being  diluted to ease the handover of forest land to mining. That means destroying biodiversity and also means a threat to water security and water quality. Even if the next generation of coal power plants are cleaner, India will pay dearly in environmental costs of lost forest cover and degraded water supply.

I am not  trying  to make light of the challenges that India faces, but with nuclear energy taking a backseat because of large capital costs and a whole different set of environmental fears and no prospect of  a quick ramping up of natural gas from conventional and shale gas reservoirs (reserves may not be enough anyway),  I don't see how reliance on coal can be reduced in the near future.

Wednesday, November 25, 2015

Agriculture Changed Us

.. and I don't mean just culturally,  but biologically as well.

Carl Zimmer in the New York Times summarizes recent results from a wide ranging study which incorporates the genetics of extant as well as ancient Europeans. The study found evidence for several instance of natural selection altering height, digestion, skin color and our immune system.

from the article:

Previous studies had suggested that Europeans became better able to digest milk once they began raising cattle. Dr. Reich and his colleagues confirmed that LCT, a gene that aids milk digestion, did experience intense natural selection, rapidly becoming more common in ancient Europeans. But it didn’t happen when farming began in Europe, as had been supposed. The earliest sign of this change, it turns out, dates back only 4,000 years.

While agriculture brought benefits like a new supply of protein in milk, it also created risks. Early European farmers who depended mainly on wheat and other crops risked getting low doses of important nutrients.

So a gene called SLC22A4 proved advantageous as soon as Europeans started to farm, Dr. Reich and his colleagues found. It encodes a protein on the surface of cells that draws in an amino acid called ergothioneine. Wheat and other crops have low levels of ergothioneine, and the new variant increases its absorption. That would have increased the chances of survival among the farmers who had the gene.


People who are followers of the going back to a hunter gatherer Paleolithic diet fad, take note. Our digestive arsenal and our micro-biomes have responded to a different agricultural food combination. Human evolution did not freeze with the coming of the ice age. Agriculture and animal  domestication have pushed evolution into changing our DNA.

For a more detailed treatment on human evolution over the Holocene, I recommend strongly Gregory Cochran and Henry Harpending's book - The 10,000 Year Explosion: How Civilization Accelerated Human Evolution.

Saturday, November 21, 2015

The Hobbit Evolved From Homo Erectus

That goblin of South East Asian forests continues to fascinate:

Abstract

Homo floresiensis is an extinct, diminutive hominin species discovered in the Late Pleistocene deposits of Liang Bua cave, Flores, eastern Indonesia. The nature and evolutionary origins of H. floresiensis’ unique physical characters have been intensively debated. Based on extensive comparisons using linear metric analyses, crown contour analyses, and other trait-by-trait morphological comparisons, we report here that the dental remains from multiple individuals indicate that H. floresiensis had primitive canine-premolar and advanced molar morphologies, a combination of dental traits unknown in any other hominin species. The primitive aspects are comparable to H. erectus from the Early Pleistocene, whereas some of the molar morphologies are more progressive even compared to those of modern humans. This evidence contradicts the earlier claim of an entirely modern human-like dental morphology of H. floresiensis, while at the same time does not support the hypothesis that H. floresiensis originated from a much older H. habilis or Australopithecus-like small-brained hominin species currently unknown in the Asian fossil record. These results are however consistent with the alternative hypothesis that H. floresiensis derived from an earlier Asian Homo erectus population and experienced substantial body and brain size dwarfism in an isolated insular setting. The dentition of H. floresiensis is not a simple, scaled-down version of earlier hominins.

Open Access

Monday, November 16, 2015

Field Photos: Back Country Roads Of Deccan Volcanic Province


 These are the twin pinnacles of Tail Baila, a popular trekking spot near the Western Ghat escarpment about 100 km west of Pune. I get asked often whether Tail Baila is  a volcanic plug or a dyke. It is neither. The pinnacles  are lava  flows. There is a strong structural control over  erosion in  this part of the Deccan Volcanic Province. Take a look at the satellite imagery below.


I have marked in orange arrows, a strong roughly N-S oriented fracture system. In yellow arrows is a less prominent E-W oriented fracture system. The white dotted line is the Western Ghat Escarpment. These fracture systems have their origins in the tensional forces that broke apart fragments of Gondwanaland, with the Indian continental block separating from Madagascar around 88  mya and Seychelles breaking off from the Indian block about 66 mya. The latter rifting event coinciding with India drifting over a hot portion of the mantle known as the Reunion hotspot also triggered Deccan volcanism. Many of these fractures acted as conduits for magma to rise to the surface and spread as massive lava flows. Magma still occupies some of these fractures. These clogged up pipes are called dykes.

A paleo-geographic reconstruction of India in relation to other Gondwana continents and Asia during Deccan volcanism 66 million years ago is presented below.


Source: Sankar Chatterjee et.al. 2013

The legacy of these ancient tensional gashes didn't end with Deccan volcanism but has influenced the evolution of the landforms we see today. Since the lava pile is fractured, physical weathering -aided by water seepage, disruption by plant roots and by temperature changes- peels off slabs of lava along these weak fractures faces. Rock falls are a common site at the base of many cliffs. Removal of blocks of lava eventually results in the formation  of isolated mesas, buttes and pinnacles, remnants of once continuous lava flows. Streams follow narrow fracture zones and carve out steep sided canyons. The result, after eons of weathering and erosion, is a spectacular landscape with plateaus, narrow valleys,  high basalt cliffs  and pinnacles shaped as rectangular blocks like Tail Baila. 

Update- November 17 2015: Since this topic is of great local interest let me add another thought. The Western Ghat escarpment also has been undergoing this type of physical weathering and erosion along cracks and fractures. The original location of this escarpment would have been tens to a hundred km west of the present line. For millions of years the escarpment has been retreating eastwards as lava blocks have peeled off the cliff face. The Deccan Plateau was much wider in the past. It is being eaten up by eastward erosion. Places similar to Tiger's Leap and Konkan Kada would have been to the west earlier in geological time!

Last Sunday I drove with some friends on one of the loveliest back country roads in this part of the country. The interactive map below shows the route looping around the backwaters of  the Mulshi Dam from village Valane to village Nive.



A gnarly trunk  of the Peepal tree with the Mulshi backwaters

 
Thick lava flows of the Deccan Traps with crude columnar jointing.
 

In a distance a pretty colorful entrance to a temple is glimpsed through the trees.


 Serene backwaters


 A lonely stretch of road through a woodland...


 opens up with vistas of grasslands, upland forests and high basalt cliffs


Throughout the Holocene this tug of war has continued... where farmland meets forest.


  Distant pinnacles shimmer in the afternoon haze
 

When I was in college, geology was a road less traveled by. I am so glad I took it.


..until the next time.

Monday, November 9, 2015

Quote: Stephen Jay Gould On Paleontology

This study of periodicity of mass extinction was published last month-

Periodic impact cratering and extinction events over the last 260 million years - Michael Rampino and Ken Caldiera.
 
The claims of periodicity in impact cratering and biological extinction events are controversial. A newly revised record of dated impact craters has been analyzed for periodicity, and compared with the record of extinctions over the past 260 Myr. A digital circular spectral analysis of 37 crater ages (ranging in age from 15 to 254 Myr ago) yielded evidence for a significant 25.8 ± 0.6 Myr cycle. Using the same method, we found a significant 27.0 ± 0.7 Myr cycle in the dates of the eight recognized marine extinction events over the same period. The cycles detected in impacts and extinctions have a similar phase. The impact crater dataset shows 11 apparent peaks in the last 260 Myr, at least 5 of which correlate closely with significant extinction peaks. These results suggest that the hypothesis of periodic impacts and extinction events is still viable.

This idea is not new and I remembered Stephen Jay Gould's essay "The Cosmic Dance of Siva" (in The Flamingos's Smile) which describes one of the early such hypothesis followed by his trademark meditations of the role of paleontology in understanding the nature of evolution  and the history of life. Gould was always irked by the opinions held by many that paleontology is a dusty sort of a science, where people spend their careers fighting over species names, and that they have nothing important to say about the theoretical aspects of evolution. A large part of his popular science writing effort was devoted to demolishing  this notion. He was very successful in it with essay after essay beautifully demonstrating the utmost importance of paleontology in highlighting life's little oddities as well as its grand patterns.

Paleontology in the early 1970's underwent something of a change in attitude. Decades before "big  data" became a buzzword, researchers led by David Raup, Jack Sepkoski,  Leigh Van Valen and Tom Schopf, to name a few,  began amassing enormous data sets on fossil characteristics and species distributions and subjected them to rigorous statistical analysis in an effort to elucidate distribution of biodiversity and macro-evolutionary trends. Gould's own work was substantial. Ideas such as "punctuated equilibrium" (with Niles Eldridge) which relies on the fossil record to tease out patterns in the mode and tempo of evolution, were met with admiration as well as fierce criticism as was his thinking on the role of contingency and chance and the limits of natural selection and adaptive evolution as explanations for life's historical trajectories. His theoretical forays did make paleontologists think more broadly about their data and what it tells us about evolution but my take is that it didn't cause a revolution in evolutionary theory as was made out by the media and by Gould's  rhetoric. But he did elevate the status of paleontology and that can only be good for science.

He writes:

Most hot  ideas turn out to be  wrong. I can only hope that I will not be remembered as the man who campaigned with a name for the nonexistent (surely worse than a moon for the misbegotten). Some chances are certainly worth taking. If Thalia smiles and Siva exists, think what it all will mean for my beloved science of paleontology. We have labored so long under the onus of boredom and dullness. We are guardians of life's history, but we are often depicted as mindless philatelists of stone; specialists in tiny corners of space, time, and taxonomy; purveyors of such arcane names  as Pharkidonotus percarinatus in extended orgies of irrelevant detail. The editors of Britain's leading scientific journal wrote of us in 1969: "Scientists in general might be excused for assuming that most geologists are paleontologists and most paleontologists have staked out a square mile as their life's work." 

That impression has changed since to include paleontology as an important contributor to evolutionary theory. For that, the field owes him a debt.

Thursday, October 29, 2015

Fossils And The Origin And Diversification Of Birds

ResearchBlogging.org
Stephen Brusatte and colleagues have a fine review article in Current Biology that brings together findings from the fossil record and molecular phylogeny work that throw light of the long history of bird evolution from Jurassic-Cretaceous to modern species.

Did you know .. that the remarkable Jehol Biota from northeastern China from 130  to 120 million years ago preserves thousands of bird fossils and accounts for nearly half of the global Mesozoic bird diversity? The Jehol Biota represents fossilization in wetland and lake sediments. The fine grained sediment size would have aided the superb preservation of these creatures. This fauna included small arborealists, semi-aquatic birds and large generalists but certain modern ecotypes like large aerial forages and aquatic specialists are not present. The End Cretaceous mass extinction produced empty ecologic niches for a greater diversity of bird forms to evolve.

..or that birds retain a single functional ovary and oviduct and a single oocycte is ovulated, shelled and laid per 24 hour cycle. Microstructural egg shell characteristics and small clutch size evolved incrementally in bird-like dinosaur ancestors who did retain two ovaries though. Earliest birds like Jeholornis and enantiornithines ( a basal group of birds) apparently had one ovary indicating that birds may have lost one ovary perhaps due to body lightening in response to the evolution of flight.

There is plenty of information in this essay on the long evolutionary history of bird like characters in dinosaur ancestors and the subsequent diversification of early (and now extinct) and post Cretaceous modern birds. It is not true that the end Cretaceous mass extinction affected only non-avian dinosaurs. Early birds had diversified into distinct groups by late Cretaceous and the mass extinction wiped out many of these lineages as well. Some lineages of the early birds (neornithines)did make it through the mass extinction. Molecular phylogeny indicates that all modern lineages formed within the first 15 million years after the extinction and then diversified quite rapidly and are today represented by 10,000 odd species.

But why write so much? The old adage " a picture is worth a thousand words" can be so true!

Just take a look at this lovely inforgraphic.


 Source: The Origin and Diversification of Birds

It summarizes the evolutionary relationship (phylogeny) of dinosaurs and birds and superimposes the evolution of traits that we recognize as typical of birds on a timeline from Triassic to the earliest birds (where Avialae/Aves branch out) . What we see is that these features evolved piecemeal over a 100 million year period in dinosaurs and some in the earliest birds, but not as a crazy spurt of morphological innovation that would have marked the geologically sudden appearance of a radically different creature.  Traits like bipedal posture, hollowed bones, wishbone, three fingered hands, wings and feathers, all appeared at successive stages in dinosaurs. Other traits like keeled breastbone to support flight muscles, endothermic metabolism and rapid growth, highly reduced tail, true muscle powered flight, and the loss of that one ovary, appeared in early bird lineages. The long story is that a lineage of therapod dinosaurs very gradually evolved bird-like characters so much so that experts find it difficult to separate bird-like dinosaurs from dinosaur-like birds.

Creationists smirk that experts can't even decide what is a bird and what is a dinosaur. Or that bird-like dinosaur fossils are younger than the earliest birds and so dinosaurs can't be the ancestors of birds. They are missing the point that the later appearance in the fossil record of bird-like dinosaurs is simply an artifact of preservation potential. This means that older bird-like dinosaurs haven't been found yet and that after birds branched out from dinosaurs the ancestral dinosaur lineage survived alongside birds. So, the sampled bird-like dinosaurs are not the direct ancestor species of birds but co-existing cousins. More importantly, the difficulty in taxonomic identification means that morphological transformations are being captured in the fossil record. This is strong evidence for evolution.

Meanwhile, just a thought from another paper I read recently on styles of diversification in the fossil record by Douglas Erwin. In the article he points out that the evolution of morphological novelty and spurts of diversification are often de-coupled  i.e.  novelty may arise in a species but that may not immediately result in an adaptive response in terms of exploitation of new resources and ecological space. Many novel traits that we recognize as typical of birds evolved much earlier in dinosaurs and it is not clear whether their evolution lead to an adaptive radiation in that dinosaur lineage. What did happen though is that at some point a threshold was crossed during maniraptoran (the closest relatives of birds) dinosaur evolution. We can think of  this as the dinosaur-bird transition. A collection of traits which had evolved piecemeal and under different evolutionary circumstances worked really well together and were co-opted and modified to serve different functions. The bird body plan then very successfully diversified into many different and new ecological roles.

Brusatte, S., O’Connor, J., & Jarvis, E. (2015). The Origin and Diversification of Birds Current Biology, 25 (19) DOI: 10.1016/j.cub.2015.08.003

Erwin, D. (2015). Novelty and Innovation in the History of Life Current Biology, 25 (19) DOI: 10.1016/j.cub.2015.08.019

Sunday, October 25, 2015

Low Emissions Due To Ecofriendly Lifestyles? India's Climate Roadmap

India has submitted its Intended Nationally Determined Contribution to the United Nations Framework Convention on Climate Change. It is a sort of a road map the country will take with regards to future carbon emissions, mitigation and adaptation.

On page two I came across this gem:

Even now, when the per capita emissions of many developed countries vary between 7 to15 metric tonnes, the per capita emissions in India were only about 1.56 metric tonnes in 2010. This is because Indians believe in nature friendly lifestyle and practices rather than its exploitation.

What a load of bollocks!

Anyone familiar with the reality of life in India will recognize this as a specious attempt to explain away the low per capita emissions.

Emissions in India are low not because of nature friendly lifestyles but because of deep poverty. Hundreds of millions of people don't have access to enough energy... and the energy they are forced to exploit like burning cow dung, charcoal, wood and rubbish to sustain themselves is deeply injurious to their health.

On the other end of the spectrum, emissions from the increasingly affluent classes living mostly in cities are beginning to catch up with the developed world.

Nagraj Adve and Ashish Kothari critique the road map. It is not "nature friendly".

Tuesday, October 13, 2015

Open Access- History Of Life Articles In Current Biology

Update: November 6 2015- The articles are no longer open access.

This is a treat!

A special section in Current Biology on the History of Life with short essays and longer reviews on a variety of evolutionary history topics. So far I have read four:

The Cambrian Explosion - Derek E.G. Briggs
The Neoproterozoic- Nicholas J Butterfield
Novelty and Innovation in The History Of Life- Douglas H Irwin
Life in the Aftermath of Mass Extinctions- Pincelli Hull


These are densely written and immensely informative articles about various aspects of the evolution of the earth and its biosphere.

Couple of passages-

..from Novelty and Innovation in The History Of Life on the different styles of diversification seen in the fossil record-

Several challenges have arisen to claims that adaptive radiations are responsible for most evolutionary diversifications. For one, many events have been identified among both living and fossil clades that cannot be explained as the outcome of diversification from a single species. Examples range from the Cambrian explosion of animals, which involved many major clades but relatively few species, to the diversification of grasses. I have already discussed cascading radiations where increased diversity was driven by ecological interactions between clades. Other diversifications, for example the spread of a genus across a continent, may be largely non-adaptive. The most striking observation, however, is the absence of evolutionary novelty associated with classic adaptive radiations. Indeed, by their nature, adaptive radiations concern the adaptive exploitation of ecological opportunities via variation on existing adaptive themes, but not the formation of the themes themselves. While the fossil record documents adaptive radiations that encompass greater morphological diversity than Darwin’s finches, mockingbirds or Anolis lizards, including the spread of insects and angiosperms, and the Mesozoic radiation of mammals, the origins of morphological novelties often seem to involve a different process.

..from The Aftermath of Mass Extinctions-

Macroevolution is shaped as much by those who survive as those who did not [3,121]; it is shaped as much by extinction, as by innovation and speciation [3,122]. More than 99% of all the species that have ever lived are now extinct [3], and the losses have often been distinctly non-random [7,8]. The largest biotic crises eliminate entire branches of the tree of life [1], drive the decline of once diverse clades [123], and lead to the radiation of new species and ecosystems [13,124,125]. In the prolonged aftermath, ecosystem change across the globe exerts an evolutionary influence distinct from the extinction itself, with a timing characteristic of the earth system (i.e., earth system succession). As such, mass extinctions should not be considered as macroevolutionary point events, but rather as prolonged intervals of varying selection spanning the mass death and subsequent radiation of taxa.

The last line adds some perspective.... that although mass extinctions are defined by death, there is also evolution, often at elevated rates, going on during this interval. Groups of organisms which are able to adjust and evolve their way through environmental crises will find and occupy emptied ecologic niches and so to speak inherit a new earth to settle and diversify.

As you would have guessed from the articles I first dived into, my interest lies primarily on the broad patterns of evolution as revealed from the fossil record. But there are plenty more biology oriented articles to capture your interest. 

Current Biology

Sunday, October 11, 2015

The Social Utility Of Archaeology

Archaeologist Graeme Barker has been working on a Neanderthal site in the Kurdistan region in northern Iraq. In August 2014 he had to leave that region due to advances made by ISIS forces. Last month he returned to continue his studies.

He makes a pointed observation on the social uses of archaeology.

You have also worked in Libya through civil war and conflict. What has driven you to persist with these digs?

People say to me they won’t go on holiday where I choose to work next, but in both cases we embarked on the excavations in conditions of stability and then events took over! But these excavations are enormous intellectual opportunities. They are ways of tackling big, fundamental questions about the human past, using the techniques of modern archaeological science.

There is also a broader social purpose. Archaeology is often thought of as a cosy sort of subject, but most of the killing that is going on around the globe relates to people's sense of whether they are similar or different to each other, all of which is rooted in how they feel about their past and where they come from. Archaeology has a huge role to play in building civil societies that are comfortable with the complexity of their past.


This is very relevant to the situation in India too, where tension between ancient social divisions erupts into communal violence from time to time. 

Thursday, October 8, 2015

Groundwater Policy: Quis Custodiet Ipos Custodes

Who regulates the regulators?

In the context of groundwater policy, who will keep an independent check on government data collection methods and analysis which informs groundwater policy decisions.

It would be nice if government scientist themselves keep refining their methods, but equally needed are independent researchers from Universities and research institutions. Rahul Gokhale and Milind Sohoni of IIT Bombay analyze Maharashtra statewide groundwater data collected over the past few decades by the government Groundwater Surveys and Development Agency. The Agency in October of each year puts out a report on the groundwater outlook for the upcoming dry season (until June of the following year). This report relies on measured groundwater levels from ~ 5000 wells and the State rainfall data. However, there is substantial variation in groundwater levels throughout the dry season and between years in most wells.  By subjecting this data to statistical analysis and modelling study Gokhale and Sohoni conclude that aggregate rainfall data is a poor predictor of groundwater levels and that unmeasured factors like extraction patterns and land use influence groundwater availability. They point a way toward refining groundwater assessment methodology by incorporating local socio-economic and groundwater use data.

Now, on the face of it the finding seems somewhat banal, that groundwater levels and availability is controlled not just by rainfall patterns but other anthropogenic factors as well. However, it is important that someone dives into large government data sets and teases out these quantitative relationships between various interacting parameters. And it is good to see an Indian government agency share data willingly.

Abstract:

This paper looks at the crucial issue of dry-season groundwater-availability in the state of Maharashtra, India. We look at the two key hydro-climatological measurements which are used to implement groundwater policy in the state, viz., water levels in 5000+ observation wells across the state and aggregate rainfall data. We see that there is substantial variation in groundwater levels within and across the years in most wells. We argue that for a large number of these observation well locations, aggregate rainfall data is inadequate to model or to predict groundwater levels. For this, we use a novel random rainfall coefficient model for the purpose of modelling the effect of rainfall in a composite setting where extraction and changing land-use data is unknown. The observed high variance of this coefficient points to significant variations in groundwater levels, which may only be explained by unmeasured anthropogenic factors. Next, we see that the uncertainty in actual groundwater levels along with scarcity are two distinct features of groundwater availability and will elicit different behaviours from the typical user. Finally, we recommend that quantitative groundwater assessment protocols of the state should move to incorporating data from which extraction and land-use may be modelled. We believe this is one of the first studies where large spatio-temporal scale data gathered by state agencies have been analysed for scientific adequacy.

and a relevant finding and recommendation:

It is necessary to recognize that scarcity and uncertainty are mutually distinct features of a groundwater regime. For example, if groundwater was scarce but certain, the groundwater-user may make  a different set of socio-economic decisions as compared to when it were both scarce and uncertain. In the first case, it incentivizes efficient use of groundwater, while in the second case, it may well lead to competitive extraction and a race to the bottom, worsening the scarcity. Indeed, the spatial coincidence of large σα with σρ seems to suggest this. This leads us to the following policy recommendations: (i) recognition of scarcity and uncertainty as separate attributes of groundwater-availability and developing indices to measure uncertainty, (ii) further work into the incorporation of socioeconomic data along with hydrogeologic and climatic data for building groundwater assessment tools. Perhaps, one relevant avenue for this is the periodic water balance computation carried out by GSDA for each watershed, every 3–5 years (see GEC’97 1997). This incorporates considerable data on extraction, irrigation, surface water bodies, and estimates of other stocks and flows. A refinement of this water balance exercise may yield better inputs for the yearly outlook for the dry season.
 

Download paper here.

Tuesday, September 29, 2015

Eukaryote Evolutionary Dynamics Through The Proterozoic

ResearchBlogging.org

No, attention on evolution need not only be on dinosaurs, mammals and other large creatures. The Proterozoic, which is dominated by microscopic life also has a very interesting evolutionary story to tell.

Take a look  at this absolutely lovely info-graphic showing number and type of non-metazoan  eukaryote fossils in sampled stratigraphic units through the Proterozoic.


This was compiled by  Phoebe A. Cohen and Francis A. Macdonald from a literature survey of described fossil assemblages of non-metazoan Eukaryotes from Proterozoic stratigraphic sections from all over the world. The results show a dynamic living world in which biodiversity of eukaryotes fluctuated, tracking global ecological triggers. The bottom panel showing lithology in which fossils are found is important. You can see that mudstone (shale) dominates. Certain types of organisms favor certain types of sediment. Also, certain parts of organisms are better preserved in certain sediment types. This means that lithology can introduce a bias to the fossil record. There is plenty of sandstone in the Proterozoic. But soft bodied organisms don't get preserved too well in sandstone.  Carbonates are not very well represented too as host lithology in the fossil assemblages recorded. The Proterozoic has lots of limestone and dolostone sequences, but just like sandstone may not preserve soft bodied organisms as well as mudstones do. Proterozoic limestones generally have been found to contain the tougher recalcitrant fragments of eukaryote cells, so there is scope for carbonate sequences to be examined in more detail for their fossil content. Moving on, take a look at the distribution of phosphatic rocks. They appear in small time windows in the Tonian in early Neoproterozoic around 1000 million years ago and then much later in the Ediacaran beginning around 630 million years ago. Phosphatic minerals preserve fine details of soft tissue, but such type of preservation is restricted to only thin time slices.

Paleogeography may also bias the fossil record. Some locations may have accumulated the right types of sediments at the right time intervals. Location with respect to nutrient inputs and basin configuration may result in peculiar or endemic biota in that particular region. Add to that is a sampling bias. Deposits in some countries as just better studied resulting in a better fossil record. A journalist asked me recently why is the Vindhyan Basin in Central India so rich in fossils. This was in the context of the Proterozoic fossil record. The answer is that Vindhyans are not the exception. There is an improving fossil record from many Indian Proterozoic basins. A recent review by Mukund Sharma and colleagues summarizes this record...  I suspect though that the Vindhyan fossil record has been examined in a more systematic stratigraphic context so as to discern macro evolutionary trends.  An excellent paper by Purnima Srivastava  summarizes such evolutionary trends in the Proterozoic fossil record of the Vindhyans. She documents simpler prokaryote communities and moderately diversified megascopic unicellular eukaryotes in the early parts of the Proterozoic. In the Neoproterozoic she documents  more diverse and complex megascopic eukaryotes including the emergence of multicellular plant (bryophytes and sporophytes) and animal clades (Ediacaran fauna).


Source: Srivastava 2012

Explanation-  Megafossils from the Vindhyan Supergroup. (a) Association of Chuaria and Tawuia comparable with Jacutianema from the Rewa Group. (b) Dichotomous branching from the Samaria Shale, Bhander Group. (c) Association of Chuaria and Tawuia comparable with Jacutianema from the Rewa Group. (d) Carbonaceous disc with a cluster of small spheroids or a scale of some metazoan, Dholpura Shale, Bhander Group. (e) Carbonaceous vesicle with dinoflagellate-like features and two notches, Samaria Shale, Bhander Group. (f ) Chuaria-like carbonaceous discsarranged within a Tawuia-like elongated vesicle, Sirbu Shale, Bhander Group. (g) Close view of the hold fast-like  structure of (f ). (h) Chuaria with prominent and well-preserved inner body/nucleus and outer ring, Sirbu Shale, Bhander Group. (i) Carbonaceous ring, a part of the hold fast, according to the model proposed by Kumar (2001) for a multicellular plant from the Sirbu Shale, Bhander Group. ( j) Chuaria with spines/notches/ budding, Samaria Shale, Bhander Group. (k) Carbonaceous disc with two spines/processes, Samria Shale, Bhander Group. (l) Very thin filaments exhibiting branching, Rohtas Formation, Semri Group, Lower Vindhyans. (m) Small carbonaceous disc, with an umbrella-like protrusion (Sirbu Shale), comparable with the problematic microfossil Kakabekia from the Gunflint Chert (Barghoorn & Tyler 1965). (n) Very small-sized carbonaceous globules scattered haphazardly in an organic gel-like matrix, Sirbu Shale, Bhander Group. (o) Carbonaceous vesicles attached on a branched filament, Dholpura Shale, Bhander Group. (p) Branched filaments of the Dholpura Shale, Bhander Group.

Continuing a little more on the journalist's question about fossil record in India, there are other locations in the Himalayas (Krol Formation, Lesser Himalayas) and Rajasthan (Marwar Super Group) that also contain latest Neoproterozic sediments and offer rich scope for exploring the biodiversity of a very interesting period of earth history.

Coming back to the paper, the authors after taking lithological and geographic biases into account find a pattern of increasing assemblage diversity from the early Proterozoic up to the Cryogenic Period, which sees a fall in diversity. Cryogenic Period or " Snowball Earth" was a phase in the Proterozoic which saw episodes of widespread glaciations. Fossil assemblage diversity increases again in the Ediacaran Period.

Here is an extract from the paper that highlights the important questions about Proterozoic evolution that the authors address:

Here, we assess the existing record of Proterozoic fossils and test the robustness of this record by investigating potential biases presented by taphonomy, fossil categorizations, regional sampling, and uncertainties in age models. We then layer on existing paleogeographic, geochemical, and climatological datasets and assess potential relationships between eukaryotic diversification and environmental change. Questions we seek to illuminate with improved datasets include: What was the relationship between eukaryotic diversification and a putative rise in oxygen (Lenton et al. 2014; Planavsky et al. 2014)? Did the breakup of the supercontinent Rodinia lead to changes in the diversity and distribution of microfossil assemblages (Valentine andMoores 1970;Dalziel 1997; Hoffman 1998)? Was the diversification of crown group eukaryotes and origin of biomineralization (Parfrey et al. 2011, Cohen et al. 2011) driven by tectonically modulated changes in ocean chemistry (e.g., Halverson et al. 2010; Squire et al. 2006)? Did increased sinking of newly evolved mineralized tests drive changes in the biogeochemical cycles and climate (Tziperman et al. 2011)? What were the effects of global glaciation (a.k.a. Snowball Earth; Hoffman et al. 1998) on microeukaryotes? Were microeukaryotic diversification and the appearance of metazoans driven by predation (Porter 2011), changing ocean chemistry, or other factors?,

The connection with the breakup of  Rodinia is intriguing. Rifting of continents beginning around 830 mya and 780 mya lead to emplacement of large igneous provinces. Weathering of these silicate rocks resulted in an increased supply of iron and phosphorous to the oceans, leading to increase in primary productivity with effects down the food chain. Likewise, an increase in oxygen content in sea water may have provided many an impetus for the evolution of eukaryote complexity and diversity. Predation, a metabolically demanding activity may have been favored, as may an increase in cell size. Certain elements like Zinc which play physiologically critical roles in eukaryotes also may have been more accessible in the enhanced presence of oxygen.

Geological processes and biological evolution are intertwined and the Proterozoic fossil record provides ample instances of it. The origins of multicellular animals lie in the latest Neoproterozoic. The much later Cambrian "Explosion" which represents the geologically rapid diversification of the triploblastic biosphere grabs all the attention, but it is relevant to point out that a lot of the molecular machinery that animal cells rely on had already evolved in unicellular eukaryotes in various protist and fungal groups. Their diverse fossil record in the Proterozoic provides us with a broader understanding of the evolution of complexity.

Cohen, P., & Macdonald, F. (2015). The Proterozoic Record of Eukaryotes Paleobiology, 1-23 DOI: 10.1017/pab.2015.25

Friday, September 18, 2015

Harappa DNA- What Could It Tell Us About Holocene Peopling Of India

Hindustan Times carried a report a few days back on the recovery of DNA from Harappa age skeletons at Rakhigarhi village in Haryana.

What could ancient DNA tell us about the Holocene population composition of  India?

Background:

Recent genetic studies of  Indian populations  shows that Indians are a admixture of two ancient populations, the Ancestral South Indians (ASI) and  the Ancestral  North Indians (ANI). The general understanding is  that ASI has been resident  in India  since the Pleistocene, while ANI ancestry -which is related to Central and West Eurasians- was introduced in India  at various times during the Holocene. ANI and ASI are deeply divergent populations having separated from each other as early as 30 thousand to 40 thousand years ago.

ANI ancestry in Indian populations decreases along a north to south cline and from upper caste to lower caste.  Indo-European speakers have a larger component of  ANI ancestry than Dravidian speakers with North Indian upper castes showing the highest ANI ancestry.

Scenarios:

Lets assume that a representative sample of Harappa society is eventually collected. What could Harappan DNA tell us?

1) There is an absence of ANI in Harappa DNA. Harappans are unmixed ASI. This would indicate that Harappans were not Vedic Aryans. It will also have implications on how farming was introduced to the Indus valley.

2) Harappans have some ANI ancestry i.e they are a mix of ANI and ASI . This would not automatically mean that the ANI ancestry was contributed by Vedic Aryans. ANI is likely a fairly diverse group i.e. different groups of ANI after separating from West Eurasians may have  migrated into South Asia at different times in the Holocene. There is a possibility that ANI ancestry in Harappans reflects the migration of farmers (Dravidian speakers?)  from West Eurasia in the earlier part of Holocene. Moorjani et al's study indicates waves of admixture of ANI and ASI,  with middle and upper castes showing multiple layers of ANI ancestry and northern Indo European language groups shows younger admixtures dates than southern Dravidian speaking groups. These have been dated to a late and post Harappan period, although the authors say that their methods may have missed earlier admixture events. I am predicting that any ANI component in Harappans will be taken by many people as confirmation that the Vedic Aryans built the Harappan civilization.

3) Harappans have some ANI ancestry with markers suggestive of Indo-Aryan people ; One example could be the proposed West Eurasian origin -13910 C>T mutation for lactase persistence which in India  shows a northwest to southeast declining pattern. This would favor the scenario that the Vedic Aryans were a part of the Harappan civilization.  And there could be other markers typical to Indo-Aryans. Needless to say, such a finding will upset linguistic reconstructions of Indo-Aryan origins (proto-Sanskrit) thought to be not earlier than 2000 B.C. 

4) Harappans are entirely ANI. This would mean that ANI co-existed alongside ASI in the Indian subcontinent but remained genetically distinct for thousands for years until admixture in late/post Harappan times.

5) Update: November 21 2015- [ Harappans are an ASI-Austro Asiatic mix, likely speaking a Munda related language. This is a wild card entry and I am basing it on a linguistic hypothesis that there are loans words indicative of a northwest India geography in the early parts of the Rig-Ved that have phonetic similarities to Munda languages. This language substrate has been termed "Para-Munda" as it occurs really on the western most fringe of the occurrence of Munda language distribution in India, and based on its linguistic properties seems to be an early branch of the Austro-Asiatic language family.  This suggests that Indo-Aryans came in contact with resident Austro Asiatic language speakers in the Greater Punjab and Gangetic plains. Genetic work on Austro Asiatic language communities suggest a somewhat later entry (~ 2300 B.C) into East India from a Laos homeland, but Harappans just might represent an early wave of migrants from the east.]

We may get clear cut answers only when we can resolve with confidence the different layers of ANI ancestry.

I'm leaning towards Scenario (2). 

Wednesday, September 16, 2015

Coral Reefs, Atolls And Sea Level Rise

Will coral reefs and atolls (coral islands) be able to keep pace with the current and projected sea level rise and remain geologically stable in the coming decades and centuries? Will atolls in  the Pacific and Indian Oceans remain habitable?

Regarding  the first question,  I came  across a couple of recent  studies that suggest that reef growth in the Pacific, Indian and Caribbean seas has historically and in the geological  past been able to keep pace with sea level rise of magnitudes equal to or even greater than the current rate of change of sea level.

In a recent issue of  Geology, P.S Kench and colleagues study six time slices of shoreline position of the Funafuti Atoll in the tropical Pacific Ocean and find out that there has been no loss of  island due to erosion by sea level rise. This part of the Pacific has experienced some of the highest measured rates of  sea level rise amounting to about 5 mm per year over the past 60 years. Their analysis showed that reef islands in this group shifted their size, shape and positions in response to sea level rise.

What could be happening? Coral reefs are prolific producers of carbonate skeletal material. As sea level rises, corals grow upwards and outwards from established communities keeping pace with the sea level rise so as to remain in the optimum water depth range. Wave energy keeps breaking down corals and produce carbonate sand which then gets redistributed and deposited in adjacent areas including island beaches. Corals thus form a renewable supply of sediment that balances sediment lost to erosion. Thus coral islands, although may change in shape and position due to changes in depositional locus will not experience any net loss of land.

Studies which go back in geological time also seem to confirm that coral reefs have often extraordinary growth rates that they can sustain for centuries and may keep up with extremely rapid episodes of sea level rise. In a special issue of Sedimentology ( Feb 2015 Open Access) on carbonate response to sea level change, Gilbert F. Camoin and Jody M. Webster document very rapid coral growth rates  using age constrained fossil coral reefs from Barbados in the Caribbean Sea and from atolls in the Pacific and Indian Oceans.

Their results show that following the melting of the global ice caps beginning around twenty thousand years ago, coral reefs kept pace with high rates of sea level rise amounting to 6-10 mm per year and astonishingly in places like Tahiti, for periods of a few  centuries, amounting to 45 mm per year. This very high rate dated to 14.65 k to 14.3 k corresponds to a Melt Water Pulse i.e. an accelerated rise in sea level due to collapse of portions of the ice sheet. Healthy reef growth means a steady supply of sediment to replenish coral island beaches, thus maintaining geological stability through periods of sea level rise.

This suggests that many coral atolls will not simply vanish beneath the waves as sea level rise in the coming centuries, although they will change their shape and positions. The other danger besides sea level rise is the changing chemistry of sea water and other biological changes that might harm coral growth. Sea water acidification may slow down the capacity of corals to build calcium carbonate skeletons, although again, studies on the impact of changing pH on coral growth have shown mixed results, with ill effects on some coral species in some locations, while others seem to have sufficient internal buffering capacity to maintain normal growth patterns. Increasing sea water temperature may also result in a) expulsion of symbiotic algae that corals depend on, thus slowing down their growth and/or b) infection by parasites that might harm the coral animal. So, there is still much to worry about the health of coral ecosystems as the earth warms and ocean temperatures rise.

Now to the second question - will coral atolls remain habitable? Habitations on these islands are built on a foundation of dead coral communities and sand which are not going to be lifted up in response to sea level rise. Although the fringing living reef communities will supply sediment to these islands, powerful storms and high tides will still pose problems. Reefs don't form water tight sea walls around these atolls and tidal surges will bring sea water further inland.

Another problem is the impact of sea level rise on groundwater. Many of these island  communities rely on a thin fresh water aquifer for their water supply. The foundation of these islands is porous Pleistocene limestone. Holocene coral communities and sand is piled up on this Pleistocene foundation to build the island. The fresh water aquifer usually occurs in this Holocene sediment. The pores and fractures in the Pleistocene limestone below the fresh water lens is filled with sea water. The contact between the fresh water aquifer and the underlying sea water aquifer is called the Thurber Discontinuity. The graphic below shows a typical cross section and hydrogeology of a coral atoll.


 Source: Bailey et. al. 2010 adapted from Ayers, J.F.; Vacher, H.L. Hydrogeology of an atoll island: A conceptual model from detailed study of a Micronesian example. Ground Water 1986, 24, 2-15

What will be the impact of sea level rise on this fresh water lens. This is an active area of study and early results seem to suggest a variety of outcomes with small fresh water lenses further diminishing while larger ones persisting. This is a complex topic with a variety of controlling parameters like amount of eustatic sea level rise, island size and shape and island topography which will channel the extent of storm wave washover. As sea level rises over the next few decades and centuries, especially on coral atolls which are experiencing erosion and loss of land, the danger of salinization of the fresh water lens is a real possibility, which will make living on these islands a difficult proposition.

Tuesday, September 8, 2015

Understanding Global Warming- Consensus Via Committees

This is an important summary by Spencer Weart, historian emeritus at the American Institute of Physics, Maryland, on the growth of our understand of the risks posed by global warming. He does not point to any particular scientist or specific scientific papers that provided "breakthroughs" in our understanding of climate change and global warming. Instead, he says that the real actors were various committees set up to collate the diverse research done on climate change and to come up with a consensus on the risks climate change poses to humans.

A closer look, if I had much more space, would certainly turn up plenty of individuals, along with lots of mistakes and controversies about details. Each new idea was first brought up by someone and then argued out at length. Our history of committees is like the swan that glides serenely on the surface while paddling furiously underneath. Still, I haven’t been telling a Whig history, reconstructing after the fact an understanding that never existed at the time. In this peculiar case a consensus was constructed by committees on the fly, a consensus that became increasingly detailed and certain decade by decade. The topic was so important that people recognized very early on that it could not be left to a few individuals making statements to the newspapers. Experts had to analyze the entirety of the peer-reviewed literature, even have elaborate computer studies done expressly for their use, and get together to hammer out conclusions that everyone could agree were scientifically sound. To be sure, in some areas they could only agree on the extent of their uncertainty, but that, too, was a genuine and important scientific conclusion.

and this on public perception ..

I submit that a major problem in communicating climate realities to the public is that the media, and everyone else addressing the public, feature individual scientists and their discoveries and disagreements. We have scarcely come to grips with committee consensus, a different kind of history of science. You will find no account digging into details of committee deliberations. I haven’t been able to do it here, and I am not sanguine about prospects for getting it done. In fact, the IPCC and the NAS and their members have been highly reluctant to make public any documents or recollections about just what goes on in the committee deliberations. Only recently, under pressure from critics, has the IPCC made its review process entirely transparent to the public. Be that as it may, I suggest historians and social scientists should give more attention to those committees. If we did, the public would have a better idea of how “science” comes to say what it does say about global warming —and a good many other issues.

Read the article here..

HT @aboutgeology 

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.