Harappan Technology, Homo Floresiensis, Foraminifera

Some exciting readings for you- 

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

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

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

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

2) Climate change and the decline of the Hobbit.

Why are small isolated populations of animals vulnerable to extinction?

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

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

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

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

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

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

Landscapes: PIndari Glacier Trail

Every time I am dragging myself back on the last day of a tiring trek in the Himalaya, I curse and swear that I’ll never do this again. And yet, here I am, exploring the Pindari Glacier area in the Kumaon. What a beauty!!

The trail begins at village Khati. This is also the starting point for the trek to Sunderdunga Glacier which I managed to do last year. A third trail to Kafni Glacier also starts here. Landslides has made a section of that trail inaccessible for the time being.  Pindari Glacier was a favorite recreation site for colonial administrators during the Raj. As a result, two comfortable guest houses were built along the trail. The first one is at Dwali, a 12 km walk from Khati. The next hut is a further 7 km walk at Phurkiya. A cot and a warm meal is available at both places. The caretaker lives there from April to late November. 

My preference has been to go to these Uttarakhand trails in early mid November. I love that season with its cold weather, clear views, and the occasional snow flurry. And the last day walk from Phurkiya camp to the glacier is breathtaking (it was 6 below zero when we started!!).

Here are some pics of the landscapes along the trail. 

A walk through the forest with a peek of the snow ridges.

Splashes of  yellow in a steep valley.

River terraces.  

T0 is the old river bed. It is now colonized by vegetation. The river then incised or cut down into the sediment creating a bench or a terrace clinging to the valley side. There was a second phase of sediment accumulating on the new river bed followed by another incision, creating the T1 terrace at a lower level. I love to observe these changing behavior of rivers as I walk along. 

Organic red pigments have colored these boulders in the Pindari river bed.  

Dwali campsite which you get to by crossing this rickety wooden bridge over a fast flowing river.  

Ahead of Phurkiya camp, walking towards the glacier, the valley widens, opening up some great views. 

Pindari Glacier, still about 3 km walk away.  

At "Zero Point", standing on a narrow lateral moraine!  

Listen to an afternoon rain shower in a High Himalaya valley, near Phurkiya campsite. 

Above the tree line. These glacial valleys are harsh, desolate, and beautiful.

 Until next time...

Deccan Traps: Thickness And Elevation

I recently read Peter Brannen’s excellent book “The Ends of the World: Volcanic Apocalypses, Lethal Oceans And Our Quest To Understand Earth's Past Mass Extinctions”. He has packed quite a few details on the geologic triggers and ecologic upheavals the earth has witnessed from time to time, resulting in the episodic reorganization of the earth’s biosphere.

In the chapter on the Late Cretaceous mass extinction he writes, referring to the Deccan Basalts, .. “today in Western India, 11,500 -foot-tall bar-coded mountains, like the jagged banded peaks of Mahabaleshwar have been carved from this surfeit of molten rock”.  He presents a lively discussion on what impact such a prolonged phase of volcanism could have had on environmental health and biodiversity. 

The view below of a section of the Deccan Basalts at Warandha Ghat, SW of Pune city, illustrates nicely the 'bar coded mountains" that Brannen mentions. 

 

Repeated effusion of lava which spread rapidly away from eruptive vents has produced the distinct layered architecture.  Differential weathering of softer and hard layers produces intermittent rubbly vegetated slopes alternating with scarps resulting in a "bar coded" edifice.

But what about the 11,500 foot tall reference? "Tall" will be read by most as elevation. That is a curious number since the "jagged banded peaks" of the popular hill station of Mahabaleshwar are around 4700 feet high. The highest region in the Deccan Volcanic Province is Kalsubai near Nasik, standing at 5400 feet.

Why such a large discrepancy between Brannen and the measured elevation in the Deccan Volcanic Province? I suspect what Brannen is referring to is a composite stratigraphic thickness of the lava in Western Maharashtra. Refer to the table below. It presents two different approaches to organizing the lava pile into discrete units. 

 Source: Vivek S Kale and coworkers 2017- Geological Society of London, Special Publications. 

"Lithostratigraphy" relies on systematic physical differences in lava packages to classify them into formal units. The "Chemostratigraphy" classification uses chemical differences in successive phases of eruption to subdivided the lava pile. 

Add up the thickness of the individual units and you end up with a 3400 meters or 11,150 feet thick section of lava. Branner may have used a slightly different estimate of lava thickness to arrive at a 11,500 foot thickness for the Deccan Basalts. 

If, as seen in the section at Warandha Ghat, the lava is nearly horizontally disposed, why then is the stack of lava "only" 4700 feet at Mahabaleshwar and caps out at 5400 feet at Kalsubai? 

The answer is in the way the different subunits of the lava are exposed all across the volcanic province. The map below shows sections of the Deccan Traps at different locations.

 

Source: L Vanderklyusen and coworkers 2011- Journal of Petrology.

In this map, the chemostratigraphic subdivisions are shown. What is important is that all the subunits never stack up in any one place. The reason is in the regional structure of the volcanic pile. It is in the form of a gently waveform with younger packages of lava offlapping towards the south. 

Source: M. Widdowson and K.G. Cox 1996: Earth and Planetary Science Letters.

This north to south cross section of the Deccan Traps along the Western region shows how different subgroups are exposed along the profile. You can see how at any one place the lava thickness and altitude is between 1000 to 1500 meters ASL.

It is important to mention that this is a regional view of the lava section across a distance of around 650 km depicted with a 40x vertical exaggeration.  The inclination of the lava layers is very subtle and has been deduced from careful measurements of the altitude of the subunit boundaries at different locations along the profile. 

The section below shows a close up of the lava stratigraphy along two north to south profiles in mid Western Maharashtra in the well known Harishchandragarh - Bhimashankar area. Notice again how only a few of the units stack in any one location.  

Source: Vivek S Kale and coworkers 2017- Geological Society of London, Special Publications.

Why did such an arrangement of the lava units emerge? Is the waveform a regional volcanic dome with lava radiating from one central eruptive center? Or is it due to post-eruption arching of the crust? Have younger lava sections been removed by erosion from the northerly locales, or has there been a southerly migration of eruptive centers over time, resulting in the offlapping arrangement? Anne E. Jay and Mike Widdowson in a study published in the Geological Society of London estimate that as much as 1.5 km of lava section has been removed by erosion from the Nasik area. That region would have stood much taller tens of millions of years ago. We will leave these questions lingering for another time. 

What I do wish is that Mahabaleshwar really stood 11,500 feet tall. I could have ice skated on Lake Venna. 

Dinosaur Engineers, Laterite Plateau, Social Insects

The latest batch of readings and a video for you readers.

1) How the death of the dinosaurs reengineered Earth. Here is an interesting linkage between dinosaurs, sedimentary rock type distribution and river geometry. Fluvial sedimentary environments are different before (Cretaceous) and just after (Paleocene) dinosaur extinction.

In the latest Cretaceous, large bodied dinosaurs destroyed riverside vegetation, destabilizing banks and preventing stable meanders. Natural levees were breached causing sand to spill onto the floodplains, resulting in an open riverine environment. Post dinosaur extinction, vegetation growth stabilized banks, forming stable channels and meander belts, promoting a sharper division between the constrained channel sands and surrounding floodplain fine mud and organic rich swamps.

Ecosystem engineering by dinosaurs!

2) The Rocky Life: Plateaus of the Monsoon. South of the town of Satara in Maharashtra, the crest of the Western Ghats is mantled by a thick hard iron rich soil known as laterite. This red crust is a deep weathering profile that developed by chemical breakdown of the Deccan basalts (in Maharashtra) and of Precambrian metamorphic rocks (Goa and southern Western Ghats) around 50 million years ago in the Eocene during a warm and wet climate phase. For long, these high regions were treated as "wastelands", devoid of vegetation and wildlife. 

But as biologist Varad Giri explains in this excellent video, there is a hidden world that a careful observer will notice. 

And conservation biologist Neha Sinha writes about (under paywall) the plant life on these rocky plateaus- Why India's "wastelands"are biodiversity hotspots in disguise.  As she evocatively wrote about the Kaas Plateau near Satara on her X timeline- "Lakhs of flowers - carnivorous, parasitic, wild, mesmerising, ephemeral, resilient".

3) One mother for two species via obligate cross-species cloning in ants.  Social insects must rank as some of the most amazing creatures.

In one species of ants, the mother gives birth to offspring of two different species! This happens because the mother uses sperm from another species male to produce the worker caste.

Yes, they have caste too!

I’ll reproduce the abstract here and leave you to roll your eyes in wonder-

“Living organisms are assumed to produce same-species offspring. Here, we report a shift from this norm in Messor ibericus, an ant that lays individuals from two distinct species. In this life cycle, females must clone males of another species because they require their sperm to produce the worker caste. As a result, males from the same mother exhibit distinct genomes and morphologies, as they belong to species that diverged over 5 million years ago. The evolutionary history of this system appears as sexual parasitism that evolved into a natural case of cross-species cloning, resulting in the maintenance of a male-only lineage cloned through distinct species’ ova. We term females exhibiting this reproductive mode as xenoparous, meaning they give birth to other species as part of their life cycle”.

I love the first line-  Living organisms are assumed to produce same-species offspring. After all, we never tried too hard to prove it!

Will Earth Become Venus?

I came across an article written by economist Sanjeev Sabhlok on the long term climate future of the earth titled - Limestone proves the impossibility of a runaway greenhouse effect on Earth.  Mr Sabhlok has been reading some geology and has found out that the earth can naturally regulate the earth's carbon dioxide levels over geologic time.

The process operates like so: During times of increased volcanism, CO2 levels in the atmosphere increase to a point where the earth starts warming. This in turn enhances rock weathering reactions which pull back CO2 and washes it down into the ocean where it is sequestered as a bicarbonate or carbonate molecule. A fraction of this carbonate gets locked up in limestone precipitating on the sea floor. 

Besides this mechanism, photosynthesis also pulls out CO2 from the atmosphere. This CO2 goes into building organic molecules. Some of  that organic matter sinks to the ocean floor and is buried, creating another long term carbon sink.

All these natural adjustments to atmospheric CO2 means that a runaway increase where CO2 levels keep rising thousand fold unabated is unlikely to occur. Earth will not turn into a Venus. Mr Sabhlok says that most climate scientists ignore this natural regulator in their panic over a runaway greenhouse effect.

Mr Sabhlok has written quite a nice summary of the geological evolution of the earth's atmosphere. But he entirely misses the point about why scientists ignore geologic sequestration of CO2 in their climate change projections. They do so because it works too slowly to matter to us. Our concern is not a distant future where surface temperatures may or may not reach a Venus like 450 deg C, but one where there is a spike of 3-4 deg C in the next few decades to centuries which nevertheless will result in extreme damage to human society and the ecosystems we depend on.

The geologic thermostat that Mr Sabhlok describes can't prevent these smaller shorter time scale perturbations in atmospheric conditions. Some numbers he shares demonstrates the inadequacy of weathering to neutralize CO2 at short time scales. He quotes from a video put up by a Dr. Johnson Haas; " Typically on an annual basis … about 0.03 gigatonnes of carbon is extracted from the atmosphere and goes into limestone which goes into long-term geologic storage. … [E]ven at that slow rate the drawdown of CO2 from our atmosphere by shell building organisms … would completely exhaust the atmosphere of CO2 in less than a million years”. 

What he doesn't add is the impact of human emissions. Our activity is emitting an eye popping 40 billion tons of CO2 to the atmosphere every year. This is 2 orders of magnitude more than what limestone can suck in. About half of this CO2 gets absorbed by the ocean, the vast majority getting locked as a stable bicarbonate molecule (HCO3). The rest remains in the atmosphere, cumulatively increasing its CO2 levels. Over the past 250 odd years, human activity has increased the amount of CO2 in the atmosphere by about 1.5 trillion tons.

When emissions eventually go to zero, absorption by oceans will quickly start reducing atmospheric CO2, putting the brakes on warming. And in the long run, several hundred to a few thousand years after we achieve a net-zero emission scenario,  CO2 levels will come down to pre-Industrial amounts. But as long as emissions continue, the earth will keep warming and become a very unpleasant place. The geologic past informs us of the havoc wrecked by increased CO2 levels and a warmer earth. The Late Devonian (372 million years ago), the Late Permian (252 million years ago), and the late Triassic (201 million years ago) mass extinctions were all triggered by increased CO2 levels and warming from sustained volcanism.

The Inter Governmental Panel on Climate Change Synthesis Report outlines many scenarios that might unfold towards the year 2100. No contributing climate scientist on that report is panicking about a runaway greenhouse effect. Instead, they highlight that incremental increases in temperature over the next few decades will place a debilitating burden on our society through myriad impacts on our health, water security, agriculture, and biodiversity. While fixating on an implausible runaway effect, Mr. Sabhlok stays silent on the real impending danger that we are facing.

His sanguine advice that "We should sleep soundly, knowing that no matter how much CO2 mankind emits by burning fossil fuels, our amazing living planet will never go the way of Venus" is utterly irresponsible. 

Earth may never go the way of Venus, but if we don't stop burning fossil fuels our amazing planet will turn into a living hell for us and our immediate descendants. 

____________________________________________________________

Fun Facts: I didn't want to quibble about some of the specifics in my post, but I want to share this with you. 

1) Biocalcification (limestone formation) results in the emission of CO2! Since most of the carbonate in the ocean is in the form of HCO3, we can write the precipitation equation as- 

Ca + 2HCO3 -----> CaCO3 + H2O + CO2 --------- Eq.1. 

For every molecule of CO2 that gets locked up in limestone, one molecule is released in the ocean and eventually into the atmosphere.  Limestones over time do constitute a CO2 sink, but precipitation of carbonate sediment is not that effective an offset of atmospheric CO2 in the here and now. 

2)  On the other hand, dissolution of CaCO3 in the deep ocean adds alkalinity,  neutralizing the increase in ocean acidity due to CO2 released by the oxidation of organic matter. It is Eq.1. in reverse.

CaCO3 + H2O + CO2 ------> Ca + 2 HCO3 ----- Eq.2. 

Carbonate equilibria can be counterintuitive and complex! 

3) Mr Sabhlok says that "we are currently close to the lowest levels of CO2 in the Earth’s history". It is true that CO2 levels have steadily decreased over geologic time. But they have sharply increased in the past 150 years from 280 ppm in the late 1800's to more than 400 ppm today and will continue to increase as long as we keep burning fossil fuels. The last time earth saw such CO2 levels was 14 million years ago.