Thursday, May 9, 2019

Links: Petroglyphs, Language, Urban Groundwater, Dams

Some interesting articles I came across past few days.

1) Pleistocene Rock Art in India- New York Times covers the discovery of ancient rock art (40k-10K yr old?) carved on laterite plateaus of Ratnagiri District, S. Maharashtra. Good to see credit given to the stellar work of two amateur archaeologists Sudhir Risbud and Dhananjay Marathe.

Link: Ancient Rock Art In The Plains Of India.

2) Language Evolution- Linguistic analysis suggests that the Sino-Tibetan language family originated about 7200 years ago among millet farming communities in northern China.

Links: Paper - Dated language phylogenies shed light on the ancestry of Sino-Tibetan.
Summary - Origin of Sino-Tibetan language family revealed by new research.

3) Urban Groundwater- This is an issue that is gaining importance as cities in India grow and municipal water supply from surface reservoirs becomes inadequate. S. Vishwanath crunches some numbers on the ground water potential of the shallow aquifer underneath Bengaluru. It comes to more than hundred billion liters! Similar situations exist underneath other Indian cities as well, but urban groundwater has been a neglected area of study. More quantitative understanding of aquifers is needed along with a focused effort to recharge ground water.

Link:  Revisiting The Shallow Aquifer

4) Environmental Implications of Pancheshwar Dam, Uttarakhand - A review in Current Science of environmental concerns regarding the proposed Pancheshwar Dam in Uttarakhand implies that critical aspects of seismicity, slope instability, and high sedimentation rates have not been addressed in detail during the planning stages in the environment impact assessments carried out so far.

Link: Environmental implications of Pancheshwar dam in Uttarakhand (Central Himalaya), India.

Tuesday, April 30, 2019

Eastern Ghats- The New Kid On The Block

We who live in the Deccan Volcanic Province in and near about the Western Ghats generally look down upon the Eastern Ghats. Call them the poor man's mountains. Point out that the Eastern ranges have a more gentle topographic profile than the Western ranges. We smirk at the lack of spectacular escarpments, narrow gorges and the mesas and pinnacles.

But, when it comes to geology, the Eastern Ghats more than holds its own. In fact, it has a much more complicated and interesting geologic history than the Western Ghats, at least the Deccan Volcanic part of the Western Ghats.

The Deccan Volcanic part of the Western Ghats is an elevated plateau which formed by the piling up of lava 66 million years ago and which since has been dissected by rivers, forming gorges, narrow valleys, and high relief. The edge of this plateau is the Western Ghat escarpment. The Eastern Ghats on the other hand is an ancient orogenic belt which formed by the collision between crustal blocks, resulting in the formation of fold mountains.

The map below shows the broad geology of the Eastern Ghat with the inset showing its location within the Indian continent.


Source: Relative Chronology in High-Grade Crystalline Terrain of the Eastern Ghats, India: New Insights: Samarendra Bhattacharya, Rajib Kar, Amit Kumar Saw, Prasanta Das 2011.

The Eastern Ghats is a Late Archean to Proterozoic age crustal block that has evolved through long and multiple episodes of magmatism, metamorphism and deformation.  It contains rocks ranging in age from 2. 9 billion years to 900 million years old. The rocks have some of the coolest names in petrology; charnockites and enderbites, khondalites, anorthosites and syenites along with granitic rocks and  sedimentary rocks like quartzites. Charnockites (and enderbites) and khondalites are granulite grade metamorphic rocks, i.e. they formed at very high temperatures of around 900-950 deg C by transformation of older igneous and sedimentary rocks respectively. Anorthosite is an igneous rock made up almost entirely of plagioclase feldspar. Syenite is also an igneous rock containing potassium and sodium rich feldspars with no or little quartz.

The interesting part is that the Eastern Ghat block was not part of India when these rocks formed. It may have been an independent block in the Archean (more than 2. 5 billion years ago), but at some point it became part of a larger block that is now the Antarctic continent. This region then underwent magmatism around 1.7-1.6 billion years ago, an episode of granulite metamorphism around 1.6 billion years ago in its southern regions, followed by sedimentary basin formation around 1.3 to 1.2 billion years ago. These sediments were then buried, intruded by magmas like syenites,  and subjected to another episode of granulite grade metamorphism around 1.2 to 1 billion years ago. This last episode of metamorphism and deformation was a result of continental movements and collisions related to the formation of the Rodinia Supercontinent.

When did the Eastern Ghats become part of India? Geologists have timed that event to around 500 million years ago, part of the assembly of Gondwanaland.

How did they figure that out? When the Eastern Ghat terrain collided with India in the Bastar region, it caused the Baster region crust to be buried to great depths resulting in the partial melting of that crust. Radiogenic dating of minerals titanite and zircon, which formed in these new melts, give an age of around 500 million years to this melting event.

I love it when these big ideas are depicted in simple and clean diagrams. Below is a graphic that shows the separation of the Eastern Ghat terrain from its conjugate Antarctica block called the Rayner Complex.


Source: Eastern Ghats Province (India)–Rayner Complex (Antarctica) accretion: Timing the event- Pritam Nasipuri, F. Corfu, and A. Bhattacharya 2018

Two scenarios are shown. The upper panel shows a composite Eastern Ghat Province-Rayner Complex colliding with the Greater Indian landmass around 500 million years ago, followed by a breaking away of the Rayner Complex. The lower panel shows that the Eastern Ghat Province had broken away from the Rayner Complex by 800 million years ago. It then collided with India around 500 million years ago.

The Indian continent was put together by the collision and welding of several smaller continental blocks, namely Dharwar, Aravalli, Bundelkhand, Bastar and Singbhum. This assembly took place between 2 billion and 1 billion years ago.

The Eastern Ghat block was the last to join India. As recent work suggests, as late as 500 million years ago.

Sunday, April 14, 2019

Human Evolution: Stories From SE Asia

Some recent finds from SE Asia are adding detail to the complex story of human migration and population interaction, and putting a much needed spotlight on the varied geographies and ecology in which human evolution took place.

1) Anthropologist John Hawks writes about the significance of the newly reported Homo luzonensis from the northern island of Luzon in the Philippines. This hominin appears to be small bodied like the 'Hobbit' (Homo floresiensis), which lived about 700 km to the south on the island of Flores. The fossils are at least 50,000 years old and their presence suggests that SE Asia was colonized several times by different hominin populations. How they were related to each other is currently an open and actively debated question.

Link: New species of hominin from Luzon.

2) Denisovans were an archaic group of hominins who diverged from the Neanderthals more than half a million years ago and lived over wide swaths of Eurasia and SE Asia. They interbred with more recent humans entering these regions, beginning about 60,000 years ago. Living Eurasians and Papuan people carry small amounts of Denisovan ancestry. A recent genetic analysis suggests that at an early stage in their history the Denisovans split in to two or three distinct groups, which then genetically diverged from each other. Papuans carry evidence of intermixing with these different Denisovan lineages.

Link: Multiple Deeply Divergent Denisovan Ancestries in Papuans (paper)
Summary: Ancient DNA reveals new branches of the Denisovan family tree.

3) Some of the oldest cave art has recently (2014) been found in Indonesia from the southern part of Sulewasi Island. They are estimated to be around 35,000 to 40,000 years old. A nice summary in Smithsonian Magazine details the discovery. Art forms of this antiquity from Indonesia suggests that a simple story of a singular origin of human symbolic thinking is not tenable anymore. 

Link: A Journey to the Oldest Cave Paintings in the World.

Saturday, March 30, 2019

Palaeontology: Some Recent Spectacular Fossil Finds

Sharing some news on exciting fossil discoveries of the recent past:

1) Early animal evolution is a topic that continues to fascinate. A fossil rich sedimentary deposit from China dated to about 518 million years ago reveals exquisitely preserved soft bodied animals of the early Cambrian. This find, termed the Qingjiang biota, compliments the well known Burgess Shale of Canada and the Chenjiang site in China. It contains representatives of early cnidarians (related to corals), comb jellies, sponges, and many other creatures, and is helping paleontologists answer questions about the evolutionary relationships and timing of branching of animal groups.

Link: Spectacular new fossil bonanza captures explosion of early life.

2) Before the early Cambrian diversification of animals, is fossil evidence of the roots of some animal lineages, contained in the Ediacaran biota of late Neoproterozoic age ( 600-542 million years ago). At one site in S. Australia, a farmer is conserving a rich Ediacaran fossil site, turning it in to an outdoor research museum.

Link: This Australian farmer is saving fossils of some of the planet’s weirdest, most ancient creatures.

3) A 4 foot sedimentary layer in South Dakota contains a jumble of fossils of animals and plants. This 'event deposit' formed instantaneously from material gathered and dumped by a tsunami triggered by a large meteorite crashing into the Yucatan Peninsula, Mexico. Readers will recognize this! It happened 66 million years ago and resulted in the end Cretaceous mass extinction.

Link: Fossil Site Reveals Day That Meteor Hit Earth and, Maybe, Wiped Out Dinosaurs.

..and there is a longer article in the New Yorker on this fossil site and the hard work paleontologists have put in to tease out its secrets..  (thanks to Hollis for the reminder! ).

Link: The Day The Dinosaurs Died

Happy reading!

Saturday, March 23, 2019

Two Short Talks - Deccan Basalts And Geology

My friend Milind Sathe has started an arts and science outreach initiative for children named Khula Aasmaan (Open Sky). He asked me if I could give two short talks, one on my career path and experiences in geology, and the other on Deccan Basalts.

We went to a nearby hill to shoot the videos. An abandoned quarry and the basalt rock made for a pretty and relevant backdrop to the video.

Here are the links. Email subscribers who can't see the embedded video can use the permanent link to go to the Khula Aasmaan web pages for access.

1) Link- Deccan Basalts: Eruptions, mass extinctions, western ghat escarpment, ground water properties.

One correction. I mention that India broke away from Africa about 100 million years ago. It was earlier, beginning about 160 million years ago.



2) Link- Geology: My career pathway and broad interests.



Hope you like them!