Tuesday, January 26, 2016

History Of India Land Use Changes- 1880 To 2010

Notable Effort:

In India, human population has increased six-fold from 200 million to 1200 million that coupled with economic growth has resulted in significant land use and land cover (LULC) changes during 1880–2010. However, large discrepancies in the existing LULC datasets have hindered our efforts to better understand interactions among human activities, climate systems, and ecosystem in India. In this study, we incorporated high-resolution remote sensing datasets from Resourcesat-1 and historical archives at district (N = 590) and state (N = 30) levels to generate LULC datasets at 5 arc minute resolution during 1880–2010 in India. Results have shown that a significant loss of forests (from 89 million ha to 63 million ha) has occurred during the study period. Interestingly, the deforestation rate was relatively greater under the British rule (1880–1950s) and early decades after independence, and then decreased after the 1980s due to government policies to protect the forests. In contrast to forests, cropland area has increased from 92 million ha to 140.1 million ha during 1880–2010. Greater cropland expansion has occurred during the 1950–1980s that coincided with the period of farm mechanization, electrification, and introduction of high yielding crop varieties as a result of government policies to achieve self-sufficiency in food production. The rate of urbanization was slower during 1880–1940 but significantly increased after the 1950s probably due to rapid increase in population and economic growth in India. Our study provides the most reliable estimations of historical LULC at regional scale in India. This is the first attempt to incorporate newly developed high-resolution remote sensing datasets and inventory archives to reconstruct the time series of LULC records for such a long period in India. The spatial and temporal information on LULC derived from this study could be used by ecosystem, hydrological, and climate modeling as well as by policy makers for assessing the impacts of LULC on regional climate, water resources, and biogeochemical cycles in terrestrial ecosystems.

See this comparison

Source: Tian et al. 2014

The massive increase in cropland density over the Indo-Gangetic plain and the diminishing of forest over the Himalayan belts, Central India and Western Ghats is brought out starkly. The forests of the north east though appear to be in a better shape somewhat than other parts of India.

The paper makes a good point that deforestation was higher during colonial times and early days of Independence. The British saw forests as a resource to be exploited, a legacy that continued  after Independence as well. Post 1980's, Forest protection policies did put the brakes on massive deforestation. This however hides some details. Two year surveys of forest cover and forest health by Forest Survey of India reveals that denser canopy forests are being degraded, prime forest land continues to be diverted for development, and the band aid and balancing the book trick that is known as compensatory afforestation is not always meeting its goals and occasionally ends up causing more damage to the environment.

The article comes with lots of details about methodology used and a good reference list.

Open Access

Sunday, January 24, 2016

Papers- Geochemistry Of Carbonate Diagenesis

Aladin's cave has opened up! (behind pay wall)

This is for students and researchers in sedimentary geology and particularly those studying carbonate sediments. The journal Sedimentology has compiled a virtual collection of  papers from the past few decades on the geochemistry of various aspects of carbonate diagenesis ranging from impact of sea water composition and sea level changes on broad patterns of diagenesis to how crystal shapes and sizes are controlled by chemistry of fluids and micro-scale roughness of constituent sediment to oxygen and carbon isotope studies of grains and cements and what they tell us about the past groundwater systems and their interaction with rock material during sea level falls. I read some of these papers during my PhD research, especially some of the classic early work on stable isotope analysis of Pleistocence and Holocene carbonate sediments and rock from the Caribbean and the Bahamas.

One bad miss though - The Great Barrier Reef- A 700 000 Year Diagenetic History. I wrote a post on it some time back. It uses stable isotope and minor element analysis to understand how the Barrier Reef sediments have, through the Pleistocene, interacted with sea water and fresh water (during periodic sea level falls) and transformed in their physical and chemical composition. One can draw surprisingly broad inferences about the regional geological setting from chemical patterns imprinted in carbonate sediments, such as, the thickness and extent of groundwater systems, the paleo-topography, the paleo-climate and the role of surface vegetation in enhancing chemical reactions.

Diagenesis transforms sediment into rock. This is a great reference collection about this fundamental process of rock formation in carbonate environments.

Tuesday, January 12, 2016

5300 Year Old Iceman's Bacteria Genome Does Not Support Out Of India Theory

The genome of bacterium Helicobacter pylori found in  the stomach of the 5300 year old European mummy named the "Iceman" shows close similarity with Helicobacter pylori strains found in the gut of north Indians. This finding published in Science has been used as evidence to support the Out of India theory, which proposes that the Aryans and the Indo-European language family originated in India. One branch of it spread into Europe, diverging into various IE languages, while the branch which remained in India became the common  ancestor of Iranian and Sanskrit. A later migration into Iran founded the Iranian branch of the IE family.

Here is a tweet by Subhash Kak, one of the proponents of the Out of India theory.

He and others who use this finding of the bacterial genome to support this scenario are wrong.

Here's why.

Their scenario requires the European strain of Helicobacter pylori to have been derived from the Indian strain. That means people from India migrated  into Europe in the Neolithic-Early Bronze Age around five to six thousand years ago carrying with them the Indian bacterial strain which then evolved into the European variety found in the Iceman. This interpretation is demonstrably wrong. The analysis of the bacterial genomes clearly shows that the Indian strain shares ancestry with the European strain

" The resulting linked co-ancestry matrix (Fig. 4) showed that the ancient H. pylori genome shares high levels of ancestry with Indian hpAsia2 strains (Fig. 4, green boxes), but even higher co-ancestry with most European hpEurope strains".....

... "Furthermore, our co-ancestry results indicate that the Iceman’s strain belonged to a prehistoric European branch of hpAsia2 that is different from the modern hpAsia2 population from northern India".

In plain English what this mean is that the European strain has not evolved directly from the Indian strain.  Rather, the European strain and the Indian strain share an Asian common ancestor. This is clearly seen in the phylogeny (evolutionary relationship) presented in the supplementary materials of the  paper (page 50 of 88). See the image below.

Source: Supplementary Materials Maixner et al. 2016

The red arrow points to the common ancestor of the Iceman and Indian strains. The Iceman's strain and the Indian strain are sister lineages. The European strain is not derived from the Indian strain. The most sensible explanation of this finding is that from a common Asian source in the Anatolian / Near East region this bacteria spread into Europe and into India with the Neolithic expansion of farmers. It then diverged into the respective strains seen in the Iceman and in extant Indians. In Europe, this Asian derived strain then mixed with an African variety due to a migration in more recent times.

No evidence can be  found for a bronze age Out of India migration of people and languages from this study of the Iceman's bacterial genome.

Monday, January 11, 2016

Blueshist Facies And An Exam Written Long Ago

Bear with me.


Emergence of blueschists on Earth linked to secular changes in oceanic crust composition - Richard M. Palin and Richard W. White

The oldest blueschists—metamorphic rocks formed during subduction—are of Neoproterozoic age, and 0.7–0.8 billion years old. Yet, subduction of oceanic crust to mantle depths is thought to have occurred since the Hadean, over 4 billion years ago. Blueschists typically form under cold geothermal gradients of less than 400 °C GPa−1, so their absence in the ancient rock record is typically attributed to hotter pre-Neoproterozoic mantle prohibiting such low-temperature metamorphism; however, modern analogues of Archaean subduction suggest that blueschist-facies metamorphic conditions are attainable at the slab surface. Here we show that the absence of blueschists in the ancient geological record can be attributed to the changing composition of oceanic crust throughout Earth history, which is a consequence of secular cooling of the mantle since the Archaean. Oceanic crust formed on the hot, early Earth would have been rich in magnesium oxide (MgO). We use phase equilibria calculations to show that blueschists do not form in high-MgO rocks under subduction-related geothermal gradients. Instead, the subduction of MgO-rich oceanic crust would have created greenschist-like rocks—metamorphic rocks formed today at low temperatures and pressures. These ancient metamorphic products can hold about 20% more water than younger metamorphosed oceanic crust, implying that the global hydrologic cycle was more efficient in the deep geological past than today.

Blueschist facies metamorphic rocks contains a  very typical mineral assemblage of glaucophane, epidote, jadeite, albite and chlorite. The blue color  is due to Glaucophane which belongs to the sodic amphibole group of minerals.

I had read Miyashiro's book on metamorphic facies during my graduate studies in India, and then  again  as I appeared for the CSIR (Council of Scientific and Industrial Research)  scholarship exam. It served me well. One of the questions in the exam was to explain the absence of blueschist facies metamorphic  rocks from the Archean record.

There could be two explanations I had learnt. One is  that these rocks did  exist in the Archean but had been subsequently re-metamorphosed to a more stable  assemblage. The problem is to explain why there is not even a single instance where the transformation is incomplete and blueschist facies partially preserved at some Archean age subduction complex somewhere on earth. That left the other explanation as the stronger one i.e. such metamorphic rocks did not exist on earth in the Archean due to higher heat flow. I think I wrote a good answer and generally did quite well as I cleared the exam and won the scholarship.

This study also links the high heat flow on early earth to the absence of blueschist facies rocks, but in a different way. High heat flow would have meant greater amounts of partial melting of mantle rocks,  resulting in greater amounts of refractory magnesium partitioning into the magma. Such high magnesium content ocean crust then would have metamorphosed into the Mg rich greenschist type rocks instead of blueschist varieties.

The paper mentions greenschist rocks. There are plenty of them in the Archean terrains of India. The green color is due to minerals like chlorite and hornblende. They form linear belts of low-medium grade metamorphic rocks, formed by the transformation of mafic volcanic and clastic sedimentary rocks formed in an oceanic setting and deformed during events of subduction and orogeny. Some of the best metamorphic mineral collection tours are in such terrains, with rich pickings of garnet, tourmaline, flourite found in the large quartz veins that intrude these greenstone schists.  Many a college geology tours have trampled the greenstone belts of south India near the towns of Dharwad, Chitradurg  and Shimoga.

 Source: Wiki
I never had to dabble in metamorphic petrology again as my research took me a world away into carbonate sedimentology. But Miyashiro's elegantly written book I remember.

Friday, January 8, 2016

I Want This Wine!

via @geo_teira

I think the label Malbec + Malbec implies grapes from two different wineyards. ... in any case a big Argentine steak to go with it will be great too!