Early Animal Evolution - Fecal Matter

A paper published a few weeks ago on the topic of early animal evolution in the journal Trends in Ecology and Evolution caught my eye. The time period I am referring to is the Early Cambrian, roughly 539 -510 million years ago. A great diversification of animal life occurred during this interval. Many explanations for this phase of rapid animal evolution have been put forth. Expanded shallow marine habitat due to continental rearrangements, an increase in dissolved oxygen, an influx of calcium and zinc to the oceans from continental weathering, both essential for physiologic function and shell building (in case of calcium), and predator prey arms races that drove evolution of novel morphology.

The recent study by Julien Kimming and Russel Bicknell proposes that fecal matter that early animals were expelling also played a role in Cambrian animal radiation. Fecal matter is preserved as lumps of calcium carbonate known as coprolites. 

Examples of these Cambrian coprolites are shown in the collage below. They are generally centimeter to millimeter in size.

 Source- Russel and Kimmig: Trends in Ecology and Evolution, August 2026. 

The fecal lumps also contain crushed shells and disseminated organic matter containing nitrogen and phosphorous. As animals with guts became common, so did fecal pellets. These pellets began sinking into the deeper parts of oceans, bringing nutrients to previously sparsely occupied environments. Habitats increased along with more complex food webs. I’ll be writing more about early animal evolution soon, although focusing on a very different kind of fossil evidence. Stay tuned.

The author's summary of their work has been published in The Conversation.

Geology Word: Ooid

Ooids are sedimentary grains that form by precipitation of calcium carbonate around a nucleus. The nucleus may be an organic particle, or a mineral grain, or a shell fragment.

Repeated precipitation results in a concentric coating around the nucleus. Depending upon the saturation state of the sea and other variables like temperature, ooids may be made up of either calcite or aragonite. Both have the same chemical formula, CaCO3, but they differ in their atomic structure.

Ooids form in shallow seas where wave energy is vigorous. The turbulence results in the particles getting suspended and redeposited on the sea floor, resulting in an even coating around the nucleus. Beaches, tidal channels and regions near reefs are areas where ooids are accumulating today in tropical seas around the Bahamas, Caribbean, the Persian Gulf, and the Red Sea.

The picture shows an ancient ooid. This particle is around 350 million years old from the Mississippian Period, deposited in a warm shallow sea which occupied the State of Alabama in North America. I collected the rock sample on a field trip during my PhD days.

Interestingly, the nucleus is a foraminifera, a unicellular protist! Observe the coiled nature of the shell with its internal chambers visible. The shell of the foraminifera is also calcium carbonate and its precipitation is mediated by the organism. On the other hand, ooids results from an inorganic precipitation process, although there is evidence of bacterial involvement in some examples.

In the Precambrian (older than 539 million years ago), before animals evolved and began constructing shells, limestones were mostly made up of fine calcium carbonate mud. Precambrian calcium carbonate sand ( any sedimentary particle, irrespective of composition, between .063 mm and 2 mm is defined as sand) is rare, composed almost exclusively of ooids and a category of grains known as intraclasts (broken fragments of hardened sea floor).

The distribution of ooids and shell types through geologic history is a pointed reminder of how life has impacted the texture and composition of sedimentary rocks.

Deposited in high energy shoals, ooids help geologists reconstruct ancient environments and the paleogeography of continents which were flooded in the deep past.

Ooids are of interest to petroleum geologists too. The spherical grains result in a packing arrangement with high porosity (open spaces between grains). The localization of ooid layers in ancient sedimentary basins is keenly explored for their petroleum reservoir potential.

That was fun to write. I may turn this into a Geology Word series.

Bengal Delta, Africa Rifting, India Sand Mining

A few readings for your perusal- 

1) The future of Bengal Delta. With this succinct title Dipen Bhattacharya has written an informative article on the origin and evolution of the Bengal Delta. The Bay of Bengal was created when India broke away from eastern Antarctica about 130 -120 million years ago in the early mid Cretaceous. The basin expanded as India drifted northwards. From Cretaceous to Oligocene times (120-25 million years ago) rivers from Peninsular India were providing most of the sediment being deposited in the Bay. Himalaya derived sediment started overwhelming Peninsular river input from about 25 million years ago. K.S. Krishna and coworkers have very elegantly demonstrated this in their study of sediment pathways in to the Bay of Bengal.

Dr. Bhattacharya has traced the evolution of the delta into more recent times, explaining the role of the Pleistocene ice ages in delta growth. The delta’s future too is at risk with dam building and ground water extraction amplifying the changes due to global warming induced sea level rise. Well worth reading.

2) Eastern Africa Is Splitting Apart, but Not Where We Expected.  Africa is tearing apart along a north south oriented corridor from the Red Sea to Mozambique. Plate motion has formed the famous rift valleys of Ethiopia, Kenya, and Tanzania, as the crust stretches and subsides along faults. Kimberley Cartier explains the geological set up of the region and the stages in which continents break apart with oceanic basins eventually forming along the initial zones of continental rifts.

Why this region of Africa is rifting is not all that easy to explain. If you look at the plate tectonic map of Eastern Africa and the adjacent Indian Ocean and Arabian Sea you will notice that the oceanic Somalia and Indian Ocean tectonic plates are pushing into East Africa. For continents to split and be pulled apart, there have to be extensional forces generated. These are usually provided at the locus of rifting by the mantle doming up, thereby breaking and pushing the lithosphere away, and by one end of the plate subducting underneath another overriding plate. The subducting oceanic crust becomes denser and heavier as it sinks deeper, pulling the rest of the plate with it.

After the breakup of Gondwanaland, the northerly movement of the India plate through the Cretaceous was sustained by the pull force of the northern edge of the India plate sinking under Asia. On the other hand, Eastern Africa is surrounded by plate spreading zones. There is no pull force available for eastern Africa, only the localized extensional stresses due to mantle upwelling.  Is that providing adequate horizontal traction at the base of the Africa Plate for the crust to break apart and stretch? For a deeper understanding into the mantle forces responsible for this, I will recommend J Micheal Kendall and Carolina Lithgow-Bertelloni ‘s article- Why is Africa Rifting?

3)  India’s rivers bear lasting scars from relentless sand mining. Some years ago I heard a podcast on Planet Money about a Jamaican beach that was stolen. An estimated 500 truckloads of sand was hauled away in the middle of the night. Sand is big business all over the world. Indian river beds too are being plundered for their sand to satisfy the demands of the booming construction industry. Sahana Ghosh explores how scientists are surveying Indian rivers using field observations and satellite data. They are trying to track down the amount of sand being extracted and the environmental impact of sand mining.

Photo: Insect Camouflage

 I nearly missed this insect as I was sipping my evening coffee.

The rust, black, and white pattern of the insect blends into the pink feldspar, biotite, and quartz of the granite table top. When the restaurant introduced these tables in the 1980’s, insects with a passing resemblance to the table colors survived the gaze of bird predators better than individuals of the same species not having that coloration. Granite colored insects reproduced more, and the match between the insect patterning and the table top became more fine tuned over time.

I made this up. It is what is known as a “Just So Story”, named after writer Rudyard Kipling’s Just So Stories for children. Kipling wrote imaginative fantastical explanations for how animals looked the way they do. The term made its way into biology and was especially used, rather derisively, by evolutionary biologist Stephen Jay Gould as a critique of evolutionary psychology. Gould complained that the field tends to come up with imaginative yet unsupported adaptationist explanations for every aspect of human behavior. They are Just So Stories. The criticism has extended to other areas of biology too. Such as one can make about my story of the insect.

How did this particular insect species get this coloration that matches the granite? Likely its historical origins lies in a very different environment. Perhaps adaptation through natural selection in an ecologic setting of leaves and colored pebbles did play a role in the evolution of this pattern. Or perhaps it is a side effect of some other developmental changes in the insect body plan. Whatever the explanation, it is only chance that its coloration matches the table top stone.

Across The Eparchean Unconformity

An unconformity is a gap in the recording of earth's history, similar to missing pages in a book. These breaks are more common than is realized. Stratigraphers, who organize geologic history, estimate that the time spans of non deposition exceed that of episodes of deposition. These gaps could be fleeting, as in a river meandering away and then reoccupying the old channel, or they could indicate conditions of non deposition and erosion lasting tens to even hundreds of millions of years.

Geologists recognize a hierarchy with the longer lasting breaks often pointing to major changes such as a mountain building phase accompanied by a prolonged sea level fall. As sediment deposition stops, erosion will often sculpt the top of the rock formation into an uneven surface. Eventually sediment deposition will resume. Geologists term such a break between the two phases of rock formation as an erosional unconformity.

Recently, the Geological Survey of India added the Eparchean Unconformity to its growing list of Geo-Heritage sites of national importance. This is one of those major long lasting erosional breaks seen in the Precambrian terrains of India. The chosen site is near Kalinjar Fort, in Banda District of Uttar Pradesh. Image Source: Geological Survey of India.

At this location, 1.2 billion year old sandstone of the Vindhyan Basin overlie 2.5 billion year old Bundelkhand granites marking more than a billion years of non deposition and erosion. While the amount of unrecorded time is significant, the real importance of this site is in the very different earth conditions represented by the older Bundelkhand granite as compared to the much younger Vindhyan sandstone. This unconformity marks the transition between the older Archean Eon and the younger Proterozoic Eon.

The Archean was a much hotter world. Melting of the earth’s mantle was producing large batches of silica rich magma which solidified to form buoyant continental crust, small rafts at first, growing into larger blocks as time went by. Vertical crustal movements created narrow depressions which got filled with lava and sediment eroded from nearby granitic highlands. These volcano-sedimentary successions were deformed and metamorphosed, and were preserved as enclaves within the granitic terrains.

By around 2.5 billion years ago, magmatic growth of continents petered out. Geologists estimate that around 70% of the present volume of continental crust was generated between 4 billion to 2.5 billion years ago.

As the mantle cooled, the more stable continental crust became the floor for a younger generation of sedimentary basins. The processes of chemical weathering and sediment transport became more prolonged on this wide gently subsiding continental terrain. As a result, waves and currents had more time to sort sediment by size, shape, and density before it was buried.

Thick deposits sorted by size into gravel, sand, and mud are the typical features of these younger basins. At places, ocean water saturated with calcium carbonate precipitated layers of calcite and aragonite sediment, preserved today as thick limestone. The biosphere was dominated by bacteria and unicellular eukaryotes, their morphology often imprinted on the rocks as wavy layers or as small mound shaped objects.

Magmatism and continental crustal growth continued less frequently in pulses coinciding with regions of plate convergence and orogeny. This phase, before large animal life evolved, lasting between 2.5 billion years and 539 million years ago is known as the Proterozoic Eon.

The newly listed National Geological Monument at Kalinjar Fort showcases these changing earth conditions.

For many decades though, exactly where to place the Eparchean Unconformity was something of a problem in Indian field geology. There was only sparse information on the absolute age of rocks and no consensus on the time span the Archean represented. Field mapping through Peninsular India indicated the presence of a distinct erosional break between deformed and metamorphosed rocks (crystalline basement) and younger flat lying or less deformed sediments. This appeared to be the natural horizon between the Archean and the Proterozoic.

But flat lying sedimentary sequences in different Indian basins, often referred to as Purana Basins, had been deposited at different times on older deformed rocks of varying ages. In some cases the foundation of the sub-horizontal sedimentary basins was indeed Archean. In other locations, the highly metamorphosed and deformed older rocks were actually Proterozoic. That meant that the Eparchean Unconformity, as earlier conceived, was not a useful marker of synchronous changes in earth processes. Many of these doubts are summarized early in this 1968 perspective on the Eparchean Unconformity by Dr. T V V G R K. Murthy, faculty at University of Sagar.

The dates for the Archean-Proterozoic transition have now been fixed at 2500 million years by the International Subcommisson of Precambrian Stratigraphy, without any condition regarding the rock type above and below the unconformity surface. As a result, the older criteria for identifying a particular erosional break as the Eparchean interval based on only rock types and extent of deformation was no longer tenable.

We finally have an answer for the question posed by Dr. Murthy so long ago:

“Does the eparchaean unconformity become evident by recognizing Archaean and Purana formations or are the Archaean and Puranas recognized by identifying the eparchaean unconformity”.

Today, better absolute dating of rocks makes differentiating Archean from Proterozoic rocks easier. The Eparchean Unconformity though is still an informal but useful term in Indian field geology signifying the cooling trajectory of the earth’s interior, with a hotter Archean transitioning to a cooler Proterozoic.

One of my earliest encounters with the Eparchean Unconformity occurred during my graduate studies. I was assigned to map an area of the Cuddapah Basin near Gani village in Andhra Pradesh, South India. I first traveled by the Dadar -Madras (now Chennai) Express to Guntakal. There, I transferred to a medium gauge train passing through small market towns connecting a vast hinterland an urban kid like me was unfamiliar with. The train chugged along eastwards towards Nandyal. For a couple of hours from Guntakal, we were firmly on Archean terrain, an agricultural landscape interrupted by small hillocks of granitic rocks. In a distance through the late morning haze we could see the low Cuddapah hills with their distinct tilted strata.   

The train crossed the Eparchean Unconformity and entered the Proterozoic through a breach in the Cuddapah hills at Dhone Junction. Ahead was the Cuddapah Basin stretching to the horizon.

We moved through quartzites, limestone, and shale, the three predominant sedimentary rock types of the shallow marine Proterozoic continental shelf. At Nandyal I had to hop onto a bus going to Kurnool. Gani village was midway between these two places. I remember arriving at Gani late evening to a warm welcome by my host Mr. Sivanand Rao. Next morning, with maps and aerial photos, hammer, and a geologic compass I started out. A half hour walk south of Gani were outcrops of the sedimentary rocks I had to map. It was a challenging and immensely satisfying introduction to field geology.

Picture shows a very youthful me and my field guide Yanganna standing in front of a quartzite hill. Captured by my accompanying batch mate Nitin Rane. June 1987.

Someday soon I hope to retrace my steps to little Gani village. The medium gauge tracks from Guntakal to Nandyal have long been replaced by standard gauge. Express trains pass through Nandyal, eventually swerving north towards Vishakapatam, or continuing south east towards the Coromandel Coast.

From Nandyal I may hire a car to Gani. I hope to meet Mr Sivanand Rao who so graciously hosted me over two field trips. I want to walk again towards the hills made of Paniam Quartzite, a sand deposit sorted and washed clean by powerful Proterozoic tides. Today, the Kurnool-Gani solar park stands near Gani, its tilted solar panels made up of ultra pure silica wafers making up an Anthropocene analogue of the more ancient quartz rich deposits.

Photomicrograph shows the Proterozoic Paniam Quartzite classified as a “super mature quartz arenite”. Notice the well rounded quartz grains outlined by iron oxide. Location - Gani anticline.

Beyond the quartzite hills are the Vempalle Formation dolomite, a vestige of the Proterozoic ocean I first waded in to begin my life long association with carbonate sedimentology. It will be a home coming of sorts for me.

Photomicrograph shows microbial layers in the Vempalle dolomite. Dolomite crystals of different size and shape have replaced the original organic mats. Location- Gani anticline.

I have one more incentive to relive this journey. The filter coffee at Guntakal railway station canteen. It is the very best.

Iran Oil, Flowering Plants, India Aquifers

Some readings and a podcast from the past few weeks- 

1) The Geological controls on Iran Oil- Geology lovers who like to explore satellite imagery would have surely noticed the landscape of southern Iran. The crust is wrinkled up into unending fold mountains. These have resulted due to the collision of the Arabian plate with the Eurasian plate. And that convergence earlier in history created a depression which filled  with organic rich mud, the source of all that Iranian oil reserves. Stephanie Pappas has written a nice primer on the quirk of geology that explains Iran’s oil bounty.

2) How Flowers Transformed Planet Earth-  “Both in the evolution of life on this planet, and in human culture, flowers have been a critical engine of connection and cooperation”. I had enjoyed David George Haskell’s earlier book, “The Forest Unseen”, in which he observed one square meter of forest floor through different seasons to track changes in fauna and flora and what that teaches us  about ecologic relationships. Viviane Callier talks to him about his new book on flowering plants and their significance in science and society.

3) Indian Hydrogeology- Groundwater is the lifeline of Indian agriculture. That makes understanding aquifers a critical aspect of exploring and utilization of this resource. Recently, Pune based groundwater researcher Dr. Himanshu Kulkarni was awarded the International Water Prize by the University of Oklahoma for his contributions to Indian hydrogeology. They span nearly 4 decades of work in the Deccan basalts, as well as other Indian geologic terrains. His work includes not just the science of aquifers, but also efforts on involving local communities in sharing and managing this resource.

Veena Srinivasan of Well Labs has a long conversation with Dr. Kulkarni about his life’s work. On a personal note, Himanshu was my senior in University. It was really good to hear about this recognition for his important contributions to Indian groundwater science.

Deccan Volcanism And Mass Extinction

What role did Deccan Volcanism play in the end Cretaceous mass extinction? 

There is widespread agreement that an asteroid struck what is now the Yucatan Peninsula region of Mexico 66.05 million years ago. The resulting environmental catastrophe precipitated an abrupt mass extinction, wiping out 70% of all species. In the rock record, a thin clay layer preserves evidence of the extraterrestrial origin of this impact event. It is referred to as the K-Pg boundary layer, K being Cretaceous and Pg referring to the Paleogene. The biota below the boundary layer is very different from fossil assemblages above it.

The earth at that time was also experiencing a major episode of basalt volcanism. This Large Igneous Province (LIP) is known as the Deccan Volcanic Province or the Deccan Traps. Volcanism occurred both before and after the impact event. Geologists have been divided on whether most the lava erupted after the asteroid hit or before it with different implications for the role of volcanism in the mass extinction. There was also an uncertain and incomplete assessment of the volumes of lava involved.

A new paper by Vivek S. Kale and coworkers titled “Spatio-temporal volume recalibration shows Deccan volcanism caused Terminal Cretaceous Mass Extinction” leaves no room for doubt about which side of the divide this group stands. The researchers examine over 80 lava sections across the Deccan Volcanic Province and recalculate the lava volume, assigning packages of lava a time bracket based of absolute dating, magnetic signatures, and fossils. They find that around 70% of the Deccan lava erupted in a time span of 300,000 years before the mass extinction.

Their results are summarized in this infographic. Source: Vivek S. Kale and coworkers, GSA Bulletin, November 2025.

The volume estimates of previous workers and their study is shown to the left. Also presented are marine paleo-environmental indicators represented by a paleo-temperature curve and carbon isotope curves spanning the mass extinction.

A short explanation of these curves will be useful.

For estimating temperature, geologists use the ratio of Oxygen 18/Oxygen 16 preserved in the shell (CaCO3) of planktonic organisms like foraminifera or calcareous nanoplankton. During warm phases, vigorous evaporation results in more of O18 escaping into the atmosphere, enriching the ocean slightly in the lighter O16. Calcium carbonate shell growth incorporate O18 and O16 without preference, maintaining the same O18/O16 ratio of sea water .

Warmer seas will result in shells having a lower O18/O16 ratio, than shells that grow in cooler water. The temperature is estimated from these measured oxygen isotope ratios.

The increase in sea surface temperature observed here, known as the Late Masstrichtian Warming Event (LMWE), has been linked to increased CO2 emissions during Deccan Volcanism.

Carbon isotope trends through time are presented by measuring the C13/C12 ratio of the target sample. ‘Bulk’ carbon means any carbon from hard parts as against carbon from organic material. It might mean just ground up limestone made up of a mixture of shells and lime mud. Jurassic onward, the proliferation of planktonic foraminifera has allowed geologists to select shells of just one or two species for their measurements. This makes it easier to screen for post depositional alteration which could reset the original oceanic C13/C12 ratio due to reaction with fluids of a different composition. It is more difficult to recognize these effects in a mixed sample, especially one with fine calcium carbonate mud.

Variation in C13/C12 ratio through time is generally regarded as an indicator of primary productivity. Photosynthesizing organisms have a strong preference for the lighter C12 to build organic tissue. The C13/C12 ratio of organic matter is strongly depleted compared to the sea water C13/C12 ratio. Similar to oxygen intake, growing shells preserve the C13/C12 ratio of the ocean. During environmental crises, reduced primary productivity enriches the ocean in the lighter isotope, also depressing the C13/C12 ratio of shells growing under these conditions.

The modest (relative to earlier Phanerozoic mass extinctions) carbon isotope excursion coincident with the K-Pg boundary suggests a decrease in primary productivity due to the extinction of some photosynthesizing groups. In contrast, the amplitude range of the isotope excursions seen during the Late Maastrichtian Warming Event can also be explained by a non-biological driver.

Carbon dioxide of volcanic origin is isotopically lighter than sea water. Pulses of volcanism may result in a large enough pool of lighter C12 dissolving in the ocean and shifting sea water C13/C12 ratio to the depleted values measured in Late Cretaceous shells.

Kale and coworkers argue that increased volume of lava eruption and emissions of CO2 and other gases in the Late Maastrichtian caused global warming and destabilized the biosphere. Ecosystems were already tottering when the asteroid delivered the knockout punch.

Just how stressed was the ecosystem? The most visible indicator of environmental changes impacting an ancient biosphere is the fossil record of that time period. Their paper however does not present any analysis of the Late Maastrichtian biota.

The several studies (Ref. 1, 2, 3) where from Kale and coworkers source the paleo-temperature and isotope record all unambiguously conclude that the LMWE had a limited impact on marine life. Species diversity did not change much. Fossil community structure remained stable, or where it did change, it reflected migration and range shifts. An example of this is L. Woelders and coworkers study of a Late Cretaceous section from the South Atlantic where they find fluctuating abundances of benthic foraminifera and dinoflagellates tracking climate and sea level cycles.

That is not to say that organisms were unaffected by this warming event. Other studies across the marine realm have documented biotic stress. Vincente Gilabert and coworkers find fragmentation of shells, abundance of low oxygen tolerant taxa, and dwarfing of some species, in their study of planktonic foraminifera of the Caravaca section in Spain. Similarly, Gerta Keller and coworkers study on planktonic foraminifera also reveals species dwarfism and abundance of high stress opportunistic species in the late Maastrichtian of the Indian Ocean and South Atlantic.

Nicholas Thibault and Dorothee Husson in a survey of the Late Cretaceous ocean point out that nanoplankton species numbers dropped during the LMWE, but diversity rebounded and increased with no significant extinction in the last 140,000 years of the Cretaceous. Michael Henehan and coworkers infer an increase in ocean acidity coinciding with the LTME based on reduced preservation of calcium carbonate shells on the sea floor. Shell preservation and sea water carbonate saturation return to pre event values in the last 200,000 years before the K-Pg impact event.

Do these observations on plankton species signal some sort of a beginning of the end of ecosystems across the entire marine biosphere? Since Deccan Volcanism spanned several hundred thousand years, could there have been a mass extinction if there had been no asteroid hit? It is conceivable that the prolonged volcanism could have resulted in a ratcheting of environment stress, eventually crossing tolerance thresholds.

This proposition has been hard to test because the asteroid crashed the Cretaceous party denying us an extended view of a volcanism only unfolding of history.

Still, we do have a good 300,000 year record before the impact of sedimentary deposition that coincided with the most voluminous phase of Deccan volcanism. Finer scale resolution of marine sections in the past few years allow us to examine global biotic trends from this time span.

As mentioned above, the impact of ocean warming seems to be quite limited to changes in shell size, temporary species abundance shifts, and adjustments by migration to favorable locales. Importantly, there is no signal of elevated extinction in diverse groups such as planktonic foraminifera, radiolarians, nanoplankton, ammonoids, bivalves, and gastropods in the final few hundred thousand years of the Cretaceous, when volcanism was at its peak (Ref 1,2,3,4).

A closer look at the environmental proxy data is revealing. After a warming phase, the paleo-temperature curve shows a 150 thousand year cooling trend in the terminal Maastrichtian until the K-Pg boundary. Mirroring this cooling trend is a distinct shift towards heavier carbon isotope values. This may be due to increasing primary productivity signaling a general amelioration of ocean conditions.

What could cause such a cooling despite ongoing voluminous volcanism and CO2 emissions? The answer may be enhanced weathering of all that fresh basalt which kept sequestering carbon dioxide during silicate weathering reactions.

There are two lines of observation that support increased weathering during end Cretaceous times.

The first observation is the recovery of calcium carbonate saturation level of the ocean. Weathering releases divalent cations like calcium and magnesium in to the ocean resulting in an excess positive charge (alkalinity) in sea water. The charge imbalance promotes dissociation of the poorly soluble CO2 gas (represented in equations as carbonic acid -H2CO3) and the formation of more stable negatively charged bicarbonate (HCO3) or carbonate (CO3) anions, raising carbonate saturation state. A decrease in dissolved gas leads to a draw down of atmospheric CO2 in to the ocean by air-sea gas exchange. Alkalinity can also be described as the buffering capacity of the ocean against excessive CO2 buildup.

Today, rapid atmospheric CO2 increase is a major concern for ecosystem and societal health. Research and small scale demonstrations to enhance ocean alkalinity are gaining importance as we try to replicate on human time scales what nature does over much longer time spans.

The other independent support for enhanced weathering comes from another isotope system, the osmium 187/osmium188 ratio. Continental crust is enriched in Rhenium187 which decays to Osmium187. Rocks like basalt derived directly from partial melting of the mantle have much lower Rhenium187 and consequently Osmium187. There is a progressive decrease in the Osmium187/Osmium188 ratio in Late Maastrichtian ocean sediments. This is consistent with weathering and increased supply of non-radiogenic Os188 from a fresh basalt source. Some of the decline can also be explained by a reduced supply of Os187 as large areas of radiogenic continental crust were blanketed by lava.

Late Cretaceous marine ecosystem health can also be assessed by looking at the difference in the C13/C12 ratio between surface dwelling planktonic and bottom dwelling benthic foraminifera shells. This isotope gradient is maintained by the biological pump, a transfer of organic carbon and nutrients from the sea surface to depths. Organic carbon is enriched in the lighter isotope compared to planktonic shells (as explained earlier). This organic matter sinks to the ocean depths and oxidizes, enriching the Dissolved Organic Carbon (DIC) pool in C12. Shells of benthic foraminifera (bottom dwelling) have a lower C13/12 ratio than planktonic calcifiers.

A noticeable C13/C12 gradient is present (Ref. 1, 2) in the latest Cretaceous ocean. It converges immediately above the K-Pg boundary, indicating a disruption of the marine carbon cycle only after the asteroid impact.

Environmental perturbations need not precipitate a terminal decline of ecosystems. My reading of the fossil record and the different proxies is that the effects of the LMWE were transient. Key biogeochemical cycles remained intact through the Late Maastrichtian implying that volcanism did not greatly diminish pelagic ecosystem function. The end Cretaceous marine biosphere shows recovery and resilience and not signs of a ‘critically damaged’ system.

David E. Fastovsky and Antoine Bercovici perceptively ask in their review of the terrestrial record of the K-Pg extinction- “how does one weaken an ecosystem in terms of its ability to withstand catastrophic, that is to say, very short-term events? In other words, this is not a ‘straw that broke the camel’s back’ situation, where preceding events play a big role in the eventual failure. Since large swaths were simply obliterated in the asteroid’s wake, and more distant regions experienced acute shock, it wouldn’t have mattered if ecosystems were weakened or hale and hearty.

I expressed a similar sentiment earlier in the post. To attribute a causal role to Deccan volcanism, there have to be signs that significant global extinction events occurred prior to the asteroid strike. The data just doesn’t point in that direction.

Earlier in earth history, the end Permian (251.9 million years ago) and the end Triassic (201.4 million years ago) mass extinctions have been more convincingly linked to massive environmental damage triggered by sustained igneous activity. The impact on the environment due to Deccan volcanism appears muted in comparison.

One reason could be that during the Permian and Triassic igneous episodes, magma intruded through thick sedimentary basins filled with limestone, organic rich shale, and sulfur bearing evaporites. Interestingly, the mass extinction coincided with the emplacement of thick sills, tabular bodies of magma injected parallel to the strata. As a result, a surge of volatiles emanating from baking sediment amplified volcanic emissions, overwhelming the earth’s natural buffering capacity. Both these mass extinctions are estimated to have unraveled in just tens of thousands of years.

In central Peninsular India, Deccan volcanism intersected older sedimentary basins only at the northern and southern fringes. Slow cooling shallow subsurface sills facilitating effective heat transfer to surrounding crust are absent. Instead, eruptions were fed by magma ascending rapidly along thin conduits (dikes) aligned in swarms. More relevant is that only sterile granitic rocks underlie the regions where the most voluminous eruptions took place.

Volatile bearing sedimentary rocks did play a role in the end Cretaceous mass extinction. But by a quirk of fate, it was the asteroid that found them. The Yucatan region of Mexico where the asteroid hit is underlain by hydrocarbon rich sediments, and sulfur rich salt. The impact released soot and sulfate aerosols in the atmosphere resulting in global cooling and reducing photosynthesis for weeks to months. Eventually, the dust settled upon a world utterly transformed. It was the beginning of a new world, one where flowering plants, song birds, and mammals diversified and flourished. From time to time, chance events have opened up entirely new avenues for evolution to explore.

It is pertinent to stress again the paramount importance of rates of processes in the context of our developing climate crises. Although in absolute terms humans may not emit more than past large volcanic events like the Cretaceous Deccan Volcanism or the Siberian Volcanism of late Permian times, we are emitting CO2 at a rate many times faster than these natural events. Carbon dioxide is building up in the atmosphere too quickly for weathering and ocean ecosystems to offset over the next few hundred years.

Lastly, Jurassic onward, the proliferation and evolution of plankton shell building organisms such as foraminifera and coccolithophores have played an important role in regulating ocean chemistry and as a buffer against atmosphere CO2 changes. This occurs by various processes. For one, the heavy shells act as ballast, exporting attached organic matter to depths before their degradation consumes oxygen in the uppermost oceanic layer. Much of this carbon gets buried, becoming a long term carbon sink.

The other important function is sustaining the ocean alkalinity balance. Precipitation of calcite and aragonite (CaCO3) removes positive charge from the ocean, in the form of divalent Ca cations, reducing alkalinity (see previous section on weathering). This alkalinity is recovered when calcareous skeletons, falling through the water column like an ocean snow, start dissolving when they sink below a threshold depth, releasing divalent Ca ions. This process known as carbonate compensation maintains the ocean’s capacity to absorb atmospheric CO2.

The cooling trend observed in the final 150,000 years of the Cretaceous suggests that the rates of emissions during Deccan volcanism likely remained relatively low. Silicate weathering on land and enhanced ocean alkalinity coupled to weathering runoff and carbonate compensation would have substantially offset Deccan CO2 emissions, moderating their environmental impact.

In the pre-Jurassic ocean, most carbonate skeleton producing organisms lived in the water column or on the sea bed of shallow continental shelves where the sea water was saturated with calcium carbonate. Skeletons did not dissolve in this environment and the biological contribution to ocean alkalinity was limited. This changed when the more geographically widespread plankton evolved biomineralization and their skeletons began settling down to depths where the ocean water is undersaturated with calcium carbonate. The calcareous plankton ecosystem has made post Jurassic oceans more resistant to external shocks, albeit over times scales of thousands of years.

By now readers may be wanting to ask- What about the dinosaurs? Did they persist right until the asteroid hit, or did they go extinct earlier? The avian branch of dinosaurs did survive. The following section is about the non-avian groups and the terrestrial fossil record.

There would have been an extirpation of local populations of dinosaurs and other fauna and flora living in areas directly affected by Deccan Volcanism. But what about the global record?

Terrestrial environments such as lakes and rivers which can preserve dinosaur fossils are patchily distributed. Frequent erosion also removes sediment, making the reconstruction of organic diversity and evolutionary trends much more difficult than for biota living in deep sea environments.

Despite these limitations, we do have some sedimentary sections which inform us about dinosaur life and the terrestrial biosphere of the Late Maastrichtian.

In their work on peat deposits from the Western Interior, U.S., Lauren O’Conner and coworkers estimate end Cretaceous paleo-temperatures based on configuration of preserved organic compounds. Besides the LMWE, they identify shorter warming and cooling phases in the final 100,000 years before the K-Pg boundary, likely driven by Deccan volcanism. However, the impact on the biota seems limited, with no decline in angiosperm diversity until the mass extinction.

Andrew J Flynn and coworkers study in New Mexico on the Naashoibito Member, a dinosaur rich sedimentary deposit, shows that dinosaurs were diverse and formed regionally distinct assemblages during the final few hundred thousand years before the asteroid strike.

The Hell’s Creek Formation spread over the States of North Dakota and Montana also offers insights in to the terrestrial ecosystems (Ref. 1, 2, 3) . Pollen and leaf assemblages attest to a healthy end Cretaceous flora. Both show a substantial and abrupt extinction at the K-Pg boundary. Vertebrate diversity also shows no decline throughout the Late Maastrichtian.

Mammals appear to the exception here. Gregory P Wilson and coworkers detailed survey of the Hell’s Creek Formation reveals two sequential changes in mammalian fauna 650,000 years and 200,000 years before the K-Pg boundary. Apart from changes in mammal assemblages, there is a decline in the abundance of metatherians. The authors link this decline to regional environmental changes, but don’t rule out the effect of Deccan volcanism.

Dinosaur fossils at the Hell Creek section have been found to within a few tens of cm of the K-Pg boundary, representing the last few hundred to a few thousand years of the Cretaceous. Their presence in numbers comparable to lower levels of the sedimentary section negates arguments that dinosaurs were either declining or had gone extinct well before the K-Pg impact event.

The icing on the cake is some recent work by Robert DePalma and coworkers on a debris layer in the Hell’s Creek section. These chaotic beds made up of boulders and fossils was deposited by a tsunami triggered by the asteroid hit. Among other organic remains, the researchers have found a fossil hind limb of an ornithiscian dinosaur. Their work was presented at the EGU 22 General Assembly 2022 in Vienna, Austria. The peer reviewed paper is yet to be published and some scientists have expressed skepticism and called for a more detailed examination of the fossils. But this initial announcement, along with other documented dinosaur fossil finds from North America, does strongly suggest that dinosaurs were well and alive until the very day the world changed 66.05 million years ago.

Geology Books

 These come highly recommended from the experts I follow- 

All released within the past year. 

The Whispers of Rocks - Anjana Khatwa: Blending indigenous stories and modern understanding of our world. 

Strata: Stories From Deep Time- Laura Poppick: Review by Edward Valauskas. 

A Little History of the Earth- Jamie Woodward- Kirkus Review.

I hope to read them soon. Happy reading :)

Mars Geology, Ancient Art, Lake Sediments

Another bunch of readings for you : 

1) Perseverance Can Continue To Operate On Mars Until At Least 2031- The gallant rover continues its exploration. How do NASA engineers plan a route and how do team geologists decide what to sample? Terrain consideration and rock outcrops are key and so far Perseverance has aced the challenges of topography and geology. Some beautiful maps too in this article.

2) Rock art from at least 67,800 years ago in Sulawesi- How do you date rock art? The material used, mineral pigments mostly, cannot be dated directly. Often, ancient cave walls are covered with layers of calcite precipitated from water seeping along the walls. This calcite can be dated as it contains radiogenic Uranium, giving us a minimum age for the underlying art.

Rock art from Sulawesi, Indonesia, have yielded minimum dates of around 67 thousand years ago. This makes it among the earliest rock art known anywhere. Also, the location of Sulawesi, separated from Bornea by wide deep water channels, suggests that the initial peopling of Sahul around 65k involved maritime journey from Borneo to Papua. Modern Homo sapiens first reached this region sometime after 60,000 years ago.

Who then made this art? Denisovans, or some other branch of humans? The Indonesia- Papua region with an improving fossil and material record of being populated by a variety of humans is proving to be a very important area to understand human migrations and evolution.

3) Sediments reveal 2,600-year-old story of human persistence in central India- Desilting of lakes is going on in many parts of India. I say, before the JCB’s move in , send in the climate scientists. Sahana Ghosh writes about some fascinating work from the wetlands of Bandhavgarh forests in Central India. Scientists have reconstructed a climate and ecologic history going back 2600 years from lake sediment and then matched that with human cultural and political changes. Even as climate changed, humans adapted and modified landscapes. This is one of the few paleoclimate archives from Central India.

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.

Easterly Tilt Of The Deccan Plateau - Update

I first wrote about this topic in 2011 in response to a question by a reader. I thought I would update my post with some new maps and explanations. Why is there such a pronounced pattern of easterly flow of the rivers in the Indian Peninsula.  I keep getting asked this question.  It was time for an update on this interesting topic on geology and landscapes. 

The region south of the Tapi river covering the Deccan basalts and the southern Indian peninsula exhibits an easterly drainage with the rivers flowing into the Bay of Bengal. The map below shows the Indian peninsular region with easterly drainage. The Deccan Plateau is mostly but not entirely covered by the Deccan basalts. South of this region is the Karnataka Plateau with a Precambrian geology. Along the east coast there are Permian-Triassic and Cretaceous basins.

Source: Hetu C. Sheth: Deccan Beyond the Plume Hypothesis

The question posed to me was - What is the relationship between the Deccan volcanics and the easterly tilt of the Indian plateau (i.e. the plateau covering the Deccan volcanics and the southern Indian peninsular region)?

The easier more intuitive answer would have been that the western ghats provide the topography and Deccan volcanism created a lava pile that is thicker to the west and which thins to the east, thus generating an east sloping surface. Rivers follow the slope to the Bay of Bengal. 

There are some geologic age inconsistency in this answer and this also does also not fully explain why the region south of the Deccan Volcanics too has an easterly drainage. Clearly, something more is going on. 

To understand the evolution of the Peninsular drainage patterns let us look back to the time when the Peninsula didn't exist. In early Mesozoic, India was part of Gondwanaland and was joined to Antarctica and Australia to the east, and Africa to the west. The triangular shape of south India with characteristic eastern and western coastlines had not formed yet. 

How can we find out the direction rivers were flowing back then? Geologists look to clues in the sedimentary basins of that age. The composition of sand in sandstone is matched to the most likely source terrain. And current directions can be inferred from studying ripples preserved on the surface of ancient sand. 

The paleo geographic maps below shows Gondwanaland and the location of the Pranhita Godavari basin in the Mesozoic. 

 

Source: Sankar Kumar Nahak and Coworkers 2024.

West North West flowing rivers originating in the highlands of the future Antarctica and in the Eastern Ghats were funneling sediment to the basin. Much of the interior of the region that would become the southern Peninsular India was a peneplain. There wasn't much topography towards the west for an easterly drainage network to develop. 

India broke away from Antarctica beginning about 140 million years ago. A distinct eastern continental margin formed. Several NE- SW oriented basins developed along the edge of the Indian continent. Since by this time an expanding Indian Ocean lay to the east, the orientation of a natural drainage system would have been from the west towards the east. 

We can say with some confidence that by 90 to 80 million years ago, east flowing rivers originating in the interior of the Indian continent were depositing sediment along the eastern Indian margin. See this map of sediment distribution along the Indian east coast. 

 Source: K.S. Krishna and Coworkers 2016.

It shows the thickness of  Mid- Late Cretaceous sediment, ranging in age from about 100 million years ago to 65 million years ago. The sediment lobes coincide with the mouths of the Godavari, Krishna rivers and other southern rivers, indicating that the paleo Godavari and the paleo Krishna system had begun building deltas from that time. Since there were no Western Ghats then, these rivers may have been shorter, with their source somewhere in the Archean and Proterozoic terrain of Peninsular India. 

Further to the south, geologists find a similar story with the ancient Cauvery. The Cauvery basin formed when Sri Lanka detached from the Indian continent. Its delta and marine deposits too contains sediment from the Late Cretaceous. 

The easterly drainage pattern of Peninsular India developed before Deccan Volcanism and the formation of the Western Ghats. 

India broke away from Madagascar about 88 million years ago  and subsequently from the Seychelles about 66-64 million year ago. The latter separation coincided with Deccan Volcanism and the eventual formation of the western Indian continental margin. Block faulting that accompanies continental breakup would have created a north south oriented high area, which would eventually evolve into the present day Western Ghats. The thinning of the lava pile to the east also would have created an easterly slope. Rivers originating in the western highland now would flow across the length of the Peninsula. 

New streams would have incised the fresh volcanic surface as lava buried the older etched landscape. But the regional  pattern of easterly flow persisted.

Some geologists maintain that there has been some fairly recent Cenozoic age (past 15-20 million years) uplift of the Western Ghats which has accentuated relief and produced the youthful looking topography of scarps, waterfalls, and deep canyons. These earth movements would have certainly given new energy to the drainage system, but there is some geologic evidence to suggest that the streams originating in the western ghat region are antecedent to the uplift of the ranges. 

For example, in the Mahabaleshwar area easterly drainage cuts across the axis of a north south oriented gentle anticlinal structure, implying that the drainage predates the uplift and warping of lava flows. Evidence from sedimentation patterns of the eastern river deltas also show that the easterly drainage originated much earlier than the formation of the Western Ghats. 

What then created that initial slope to the east that imprinted the drainage network that continues today? 

One reason is that the eastern margin formed first. Basin formation along the eastern edge of the continent would have created a relief difference between the western interior and the eastern depressions, resulting in stream networks flowing eastwards.  Secondly, the new oceanic crust made of lava that formed when India and Antarctica separated in the Late Jurassic and Early Cretaceous would have cooled by Late Cretaceous times. Becoming colder and denser it has been sinking and dragging the Peninsular region with it. 

Earlier eastern basin formation and a tug from the floor of the Bay of Bengal may have been enough to impress an east flowing drainage. Later, the east sloping lava surface and the rise of the Western Ghats reinforced this distinction between the west and the east perpetuating the direction of river flow initiated since Cretaceous times.