Assam Earthquake, Mars Rover, Shell Coiling

It has been a long break since I shared a reading list. These are some interesting articles I came across in the past couple of months.

1) How a massive earthquake in Eastern India led to the birth of modern seismology. On 12th June 1897, a massive earthquake struck the Shillong Plateau and neighboring Assam causing widespread damage. Media reports were detailed but sensational. But they did push geologists towards developing a more rigorous science of earthquake monitoring and analysis. This is a fine piece of archival research by Utsa Bose, tracing the birth of the modern science of seismology. The role of the nascent Geological Survey of India with its first generation of Indian geologists is especially noteworthy.

2) NASA’s Perseverance Sets Off-World Record for Total Distance Driven. News from NASA informs us that the Mars Perseverance Rover has now traveled further than any vehicle ever has on another world. On October 11, the rover’s odometer clocked 45.22 kilometers surpassing the 45.16 km set by the Mars Opportunity Rover.

Perseverance’s wandering has taken it to the western rim of the Jezero Crater, an area known as “Lac de Charmes”.

Around the rover are some of the oldest rocks known in the solar system. The Jezero Crater was formed by an impact about 3.9 billion years ago and is filled with surficial impact debris, as well as rocks from Mar’s interior that were thrown up during the impact.

Since Mars lacks plate tectonics, rocks from its earliest history are preserved. On Earth, plate tectonics has recycled the initial crust that formed as our planet cooled. The geological trajectory followed by Mars and Earth before Earth developed plate tectonics may have been similar. These very ancient rocks from Mars gives us an analogue for understanding early earth geological processes.

But take a look and admire this info-graphic of the many rovers that have explored Earth, Moon, and Mars and given us so much exciting data to work with in the coming decades.

Source: NASA/JPL-Caltech.

3) Why Do These Fossil Shells Flip Their Spirals Every Few Millennia? Foraminifera are unicellular protists. Many species construct a coiled shell around the soft tissue. Most species may contain both right handed and left handed coiled shells. Scientists noticed that in a few species the direction of coiling is either predominantly right spiral or left spiral. And more interestingly, as they traced the species history through their fossil record, they found that the direction of coiling flipped between right handed and left handed every few thousands of years.

There are quite a few explanation put forth to explain this with changes in temperature of the sea water being a leading answer proposed in the early research of this phenomenon. But was it so? Or are we seeing speciation, the evolution of a new variant or species that then quickly spreads through the world’s oceans and becomes a common fossil shell to be discovered by paleontologists? A fascinating look at the evolution and ecology of foraminifera by Fanni Daniella Szakál.

Inspiration From The Galapagos Islands

From the famous Galapagos Islands comes news about a link between global warming and intensification of El Nino.

 

Imagery- Sentinel 2 Mosaic: Copernicus Browser

El Nino is a pattern of natural climatic variation which occurs when a weakening or reversal of easterly trade winds results in warm Pacific water piling up around the west coast of South America. This phenomenon depends upon subtle interactions between sea surface temperature, ocean currents, and winds, and climate models can’t reproduce these accurately. This means that often different models disagree on how El Nino might be affected by global warming.  Historical records don’t go too far back for us to assess whether there is a clear correlation between global warming and El Nino strength.

Now, a new method uses corals to tease out the temperature of sea water across centuries.

Coral skeletons grow by precipitating the mineral aragonite (CaCO3) in yearly growth bands. Scientists sampled these layers and measured the amount of element strontium and the ratio of heavy oxygen O18 to the lighter O16 in each layer. Aragonite incorporates less strontium and more O16 in warmer water. A sea surface temperature record stretching back a thousand years could be constructed.

The conclusion was that over the past 40 years, temperature swings have become more extreme in El Nino years. This finding from the Galapagos is complimented by another analysis of corals from Kiribati in the Central Pacific. Scientist have a taken a step towards a firmer understanding of the variability of this phenomenon which causes extreme weather events around the globe.

Which other important scientific studies have come out of the Galapagos?

Ahem… there is off course the visit in the year 1835 by a certain Mr. Charles Darwin. His observations there made an important but not an outsized contribution towards his theories of evolution. Darwin was just as comfortable driving home his point using the example of the domesticated pigeon as he was describing the finches and mockingbirds of the Pacific Islands.

Jeff Wallace of the University of Glamorgan in his brilliant introduction to the Wordsworth Classics of World Literature edition of The Origin of Species makes this observation: 

"Readers thus soon find themselves continually shuttled to and fro across the distance between the ‘familiar’ and the ‘other’, the domestic and the exotic, in a text which seems to disdain the very boundary lines between such distinctions. With bewildering and unpredictable variation, we encounter the women-eating barbarians of Terra del Fuego; the small Asiatic cockroach; the thickened stems of the common  and Swedish turnip; the climbing hooks  used by the trailing bamboo of the Malay Archipelago; the egg carrying folds of skin of pendunuculated centipedes; the northern and southern downs of the Weald; the sedimented beds of the mouth of the Mississippi during the glacial period. Darwin’s task at once scientifically central to his work and yet only to be achieved through a vivid and creative use of language, is to make strange or 'astonishing’ the detail of the close and familiar world, and to bring the most extraordinary facets of the alien and unknown within the realms of common understanding. His success, in a text whose fascination is undiminished if not growing as we enter the peculiar concerns of the millennium, lies ultimately in indicating that these contrasting worlds are in fact one world".  

The variation in the beak of the Galapagos ground finches and mockingbirds did inspire Darwin to think about common descent and natural selection, but the legendary finches don’t even feature in his book. The reason is he failed to label his collection systematically! On his return to England he did turn over his collection of wrens, blackbirds, and finches to the ornithologist John Gould.

To his surprise, Gould informed him that despite the great differences in their beak shape and size, the ‘wrens’ and ‘blackbirds’ were in fact all ground finches. His grab bag collection was actually a closely related group of 13 species of finches. Darwin did label his collection of four mockingbirds by island, and they too, as Gould found out, were distinct species. Gould added one more crucial piece of information. All these birds had close but not identical relatives on the American mainland.

Darwin eventually saw the significance of this observation and it became an important piece of evidence for his theory of common descent. He hypothesized that one founder population of these birds must have reached the Galapagos from the South American mainland and then diverged into distinct species on different islands. The standard depiction of an evolutionary tree with branches splitting away from a common node owes its origins to the rather disorganized collection of a wide thinking naturalist and the keen observation of an ornithologist.

Many decades later two scientists did label those finches correctly. And studied them in excruciating detail.

 I am referring to Rosemary and Peter Grant’s epic 40 year study of the morphological evolution of the ground finches of the Galapagos. These two scientists painstakingly measured the variation in beak size and shape over many generations. This they complimented by comparing their genetic differences, and using all this data pieced together a tale of their evolution through changing climate patterns and food availability. Their study has provided a powerful validation of Darwin’s idea that natural selection can shape morphologic change and specialization in populations.

Jonathan Weiner’s Pulitzer Prize winning book, The Beak of the Finch, captures this story vividly. A more updated description of this research has been provided by the two scientists themselves through their publication - 40 Years Of Evolution: Darwin’s Finches On Daphne Major Island.

The Galapagos Islands began forming about 4 million years ago. The Nazca tectonic plate is moving eastwards in the Pacific over a heat source situated deep in the earth’s mantle. The eastern edge of the Nazca Plate is sinking beneath the South American tectonic plate. Sporadic volcanism over the mantle hot spot has created a chain of volcanic islands which become younger towards the west. Volcanoes on the western islands are still active.Today, the islands and the surrounding waters are a marine reserve, offering some protection to its unique biodiversity.

Although geologically young, the specific geologic and bio-geographic circumstance of these islands have proven to be a fertile ground for science. From climate change, to evolution, to conservation biology, scientists working there continue to probe and tease out insights that are proving crucial in navigating the currents of a rapidly changing world.

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.

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.

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.

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!

Joshimath Landslide, Human Evolution, Early Animals

Sharing some of my readings over the past couple of weeks- 

1) Movement of Joshimath Landslide in India: The town of Joshimath in Gharwal Himalaya is built on an ancient landslide. Geological reports going as far back as the 1970’s had warned that excessive modification of the slope due to urbanization may result in slope movement and eventual failure. These warnings proved correct as slope movement since 2018 has caused major damage to houses and livelihoods. Landslide expert Dave Petley reports on a new study of the region that uses radar technology to track earth movements. 

It concludes that removal of vegetation, mismanaged groundwater seepage and blocked drainage paths contributed to accelerated movements of the Joshimath landslide system. There is unplanned and unregulated construction happening in other Himalayan towns. Authorities must take geological advice seriously and plan their growth accordingly.

2) The Olduvai Effect- New questions about meat eating in human origins: How about some food for thought?… I mean literally. Was meat eating connected to the evolution of larger brains in our human ancestors beginning around 2 million years ago? Paleoanthropologist John Hawks writes about recent work on East African sites across the period from 2.6 to 1.2 million years ago that throws doubt on the “meat made us human” hypothesis. 

The study he discusses finds no evidence for a systematic increase in meat eating across the studied period. The evidence also points to different hominin groups having flexible strategies for obtaining meat. But can we tie increased meat eating to one particular branch of the hominin tree? This is a very interesting article on how anthropologists retrieve and analyze evidence from sites and how the geography and time depth of sampling influence the conclusions that are drawn. 

3) Complex animals living millions of years before the Cambrian Explosion revealed by seabed tracks: What do we know about early animal life before the evolution of shells made their preservation more likely starting around 530 million years ago? That animals were present much before they acquired shells is inferred from molecular data that places their origin and diversification a good 50-100 million years before the Cambrian. But there is another way to understand animal evolution before body fossils appeared. It is through studying their movement on the sea bed. Tracks and burrows made by mobile animals start appearing in the rock record by 550 million years ago. 

James Ashworth describes some recent fascinating work that has decoded the morphology of these fossil trails and compared their shape with those made by some common modern sea floor animals. The researchers then propose that the changing shapes of trails across a 10 million year period is indicative of increasing complexity in animal locomotion. Early trails were made by simpler animals with short round bodies and limited sensory capabilities. Later in time, sinuous tracks made by worm like animals characterized by a slender anterior-posterior body profiles appear. A very clever way of understanding morphological changes during early animal evolution.

Enigmatic Sedimentary Rock Darma Valley

A late Neoproterozoic to early Paleozoic section (~600-500 million years old) of the Tethyan Sedimentary Sequence is exposed around the villages of Dantu, Boun, and Philum, in the vicinity of the famous Panchachuli Glacier in Kumaon. The lower part, made up of low grade metamorphic rocks is accessible along the many local trails. The higher summits are made up of sandstone and conglomerate. These are harder to reach, but blocks eroded from the summit can be found in streams near Boun and Philum.

Two years ago I had posted a picture of a sandstone block showing convoluted folded layers and asked whether this folding was tectonic in origin or due to synsedimentary deformation of semi lithified sediment. In the latter case, shaking of the sea floor and mass movement of sediment due to an earthquake or a severe storm results in the sediment layers contorting and deforming in various ways. 

 Sandstone in stream bed near Boun village.

I could not decide between these alternatives although I favored a synsedimentary origin of these features. My reasoning was that such deformation appears local, since there were also examples of undeformed sandstone with delicately preserved primary bedding. The short wavelength folding observed in my example also is very different from the longer wavelength folds present in the lower part of the exposed Tethyan sequence. 

Last month on a trip to Boun village I came across another block from those high ridges which I think lends additional weight to the synsedimentary deformation scenario. 

You will notice that the block is made up of a conglomerate (pebbly layer) in the lower part, overlain by a beautifully cross bedded sandstone towards the top. The ten rupee coin gives a sense of scale. The lower half of the block is a classic flat pebble conglomerate. You will realize the meaning of the term as you read along. A more detailed examination of the conglomerate hints at an unusual mode of formation. The clues lie in the four boxes I have drawn. I will focus on them one by one to make my case. This is the cross section of the pebbly layer. The bedding plane view is not exposed in the boulder.

Before that, let me put up this picture of another conglomerate. This sample too has rolled down from the high ridges near Dantu village.

Sedimentologists will be confident in interpreting this as deposition in a gravelly stream or in the surf zone of a beach. The smooth and rounded shape of the cobbles is due to long transport from the source to the site of deposition, followed by the particles rubbing against each other in a high energy current and wave environment. 

Now take a look at the pebbles in Box 1. 

They have straight and jagged sides and pointed edges. This indicates very little transport and attrition before burial. The source rock of these pebbles must have been near by.

In fact, the source can be observed in Box 2.

The dark grey elongated pebbles were derived by the breakage of the bed in the lower part of the block. The dark grey layer has a fragmented fabric.  I have outlined in yellow some larger blocks of the remnant bed. They are surrounded by smaller broken pieces. It looks like a layer which hardened quickly on the sea floor broke due to a disturbance and yielded these flat pebbles. These pebbles are called intraclasts, since they are derived from a source from within the depositional environment. The slab like shape of the pebbles suggests breakage along parallel planes of weakness. The breakage is not due to tectonic overprinting since the overlying cross bedded sandstone is not affected.

Complete disarticulation of an early cemented layer will ultimately yield individual centimeter scale pebbles which make up the pebbly layer highlighted in Box 3. 

Notice the mostly horizontal disposition of the pebbles suggesting transport in a viscous laminar flow and quick burial. The sandy matrix has prevented pebbles from bumping into each other, thus preserving their sharp faces and edges. In contrast, constant exposure to waves and currents would have resulted in the sand being winnowed out and caused these platy pebbles to be rounded, imbricated and stacked at an angle.

Fine quartz and lime mud sediment was cemented by calcium carbonate on the sea floor within a few tens of centimeters of burial. This semi lithified layer then broke during an earthquake or when the sea floor was pounded during a severe storm. 

 Box 4 captures this transition from an in-place unbroken layer which show signs of breakage towards the top. 

Slope failure and mass movement of such a layer eventually resulted in complete breakage of the rigid bed and the formation of discrete flat chips which then were deposited as a flat pebble conglomerate. Box 1 to Box 4 represent different stages of the deformation and sedimentation process. The sharp contact of the layer in Box 3 with the underlying layer (see pic of the entire block) suggests that it may be material transported from an adjacent area where an equivalent bed was completely disarticulated. 

Occurrence of slope failure induced flat pebble conglomerates have been previously observed and reported from the Cambrian age Snowy Range Formation in  northern Wyoming and southern Montanan, U.S.A.

I have observed only one example of this during my recent visit and I have proposed only a tentative answer. Without observing and understanding the stratigraphic and sedimentologic context in an outcrop I cannot be certain that it is correct. 

The association of undeformed and deformed blocks does suggest that intermittent disturbances resulting in brittle and ductile deformation of semi hardened sediment masses alternated with quieter periods of sedimentation. The overlying cross bedded sandstone is an example of deposition during quieter phases.

Flat pebble conglomerates mostly form in sedimentary carbonate environments. This make sense since rapid cementation of the sea floor by calcium carbonate saturated sea water is common. This example though is from a predominantly siliciclastic setting where quartz rich silt lithified fairly rapidly.

These conglomerates also show a peculiar temporal range. They are common in Proterozoic and Cambrian age sequences, but become exceedingly rare in younger rocks. Paleoecologists suggest that this is due to the diversification of burrowing animals that took place during the Great Ordovician Biodiversification Event about 485 to 460 million years ago. 

The churning of sediment by bioturbation kept the sediment loose and granular and prevented frequent cementation of the sea floor and shallow buried layers. Carbonate intraclasts became rarer, forming only in more geographically restricted harsh hypersaline settings. Flat pebble conglomerates give us a glimpse in to the ecology and physical properties of the sea floor before the evolutionary radiation of burrowing macrofauna.

Geological processes and evolution interact and feed off each other.  Through earth history, the formation of diverse topography and chemical environments by geological circumstance have been triggers for evolutionary innovation.  In this example, the evolution of animals making deep vertical burrows resulted in the disappearance from the geologic record of a distinctive sedimentary rock type. Yet, the churning and resulting oxygenation of the sedimentary profile opened up new ecologic spaces for the colonization and diversification of a more complex web of marine communities. 

My quest for a more complete answer to the origin of these deformed sandstone continues. 

Stream near Baun village

On my next trip to Boun I will try to find more of these blocks to gather evidence in support of my theory. Or, who knows, try to find an easier route towards those high ridges! Stay tuned.

Further Reading:

1) Rapid Uplift - Field Photos: Folds- Tectonic Or Soft Sediment Deformation?

2) Thematic Posts - Rapid Uplift- Geological Processes and Evolution.

Geology Infographics

I read a lot of technical literature on various geology topics. The papers are usually long and written in jargon filled language. It can be tough to hold your concentration and read through the paper in one sitting. What can help is a well complied figure which summarizes the ideas and the results of the study. By figure, I don't mean a graph or tabular display of data, but a graphic that presents the data with a combination of symbology, line art, text, and even images. Such infographics help in grasping the gist of the study and make reading the elaborate explanations easier (you still have to read them).

In this post I will showcase three infographics that I liked from my readings. I won't write long explanations about them, since the idea is to see if you can understand the broad findings by looking at a picture. Read the abstract of the paper to assess how effective the figure is.

1) Ediacaran Extinction and Cambrian Explosion.

The distribution through time and the changes in diversity of early complex multicellular life is depicted in this infographic. The evolutionary history of two distinct 'biotas' are tracked. The Ediacaran 'biota' is a catchall phrase that includes a diverse range of extinct large fossil organisms which may include some early animals as well. Metazoans ancestral to living animal groups are the second category. The carbon isotope curve shows two prominent deflections towards negative values, termed the 'Shuram' and "BACE" (Basal Cambrian Carbon Isotope Excursion) excursions. They are thought to indicate global environmental crises. Bookending this graphic are two diversity measures. On the left is the diversity of body fossils. On the right is the diversity of trace fossils, such as imprints, tracks, and burrows. 

Take home point. The Cambrian 'Explosion' is not about the origin of animals but their geologically rapid diversification whose roots lie a good 20 to 30 million years preceding the Cambrian events. Pulses of diversity expansion and collapse took place during that time period.

2) Dating Cave Art.

Humans have left some breathtaking artwork on the walls of caves all over the world. But how do we know when they were created? The pigments used in the drawings cannot be directly dated. One can use associated cultural artifacts to narrow down the time period. Or if lucky, mineral layers that entomb the artwork can be dated directly. This method still brackets the maximum and minimum age of the artwork. This infographic explains how artwork in a Spanish cave was dated using uranium and thorium isotopes. 

3) Angiosperm and Insect Coevolution.

I had written about this topic is detail in a previous post, but thought I'll share this infographic again. The Cretaceous was a time of great environmental shifts and changes in terrestrial biodiversity. Gymnosperms gave way to a dominance of angiosperms. The diversification of flowering plants had a large collateral impact on earth. The history of angiosperms and insect groups through the Cretaceous and Cenozoic is explained in this beautifully compiled infographic. 

If you have come across a science infographic that you particularly like, do share the link in the comments section.

Early Animals, Hominin Diets, Groundwater Governance

 A few links to interesting listening and reading.

1) Tracking the first animals on earth:  Unequivocal evidence of animals is preserved in soft sediments from about 570 million years ago. The fossil record of the Ediacaran to early Cambrian times (570 to 500 million years ago) has yielded rich information about the patterns of animal evolution. Apart from fossils, comparative genetic studies have given insights into how different animal groups are related to each other and the order of branching of these groups. Amazingly, organic molecules recovered from enigmatic fossilized taxa have been used to differentiate between animal and non-animal remains. Zoologist Matthew Cobb explains all this and much more about early animal evolution in about 30 minutes. Give it a listen! 

2) Plant-eating and meat-eating in Australopithecus: What did our ancient relatives eat? By ancient, I mean going back a million years or more. We can use isotopes of nitrogen to tease out information about diets. Carnivores have more nitrogen-15 enriched tissue than plant eaters. Carbon isotopes (C13 and C12) also yield information about the diet of herbivores. Grazers munching on grass take in more of the heavier isotope of carbon than browsers eating leaves and stems. Paleoanthropologist John Hawks discusses some recent work on nitrogen and carbon isotopes of Australopithecines and how the patterns of isotopic variation extracted from tooth enamel can be interpreted in terms of diets and life history. Fascinating stuff. 

3) Addressing Depletion in Alluvial Aquifers: Why Context Matters in Participatory Groundwater Management: India relies a lot on groundwater for agriculture. There are signs from many parts of the country of acute groundwater distress. Participatory Groundwater Management initiatives have had some success in addressing this distress. Pratik Kumar and Veena Srinivasan point out that these cooperative movements have been more successful in hard rock aquifers from different parts of the country than alluvial aquifers of northwest India. Geology matters. Aquifer properties matter. Hard rock aquifers are more sensitive to abstraction and are rapidly de-watered and recharged seasonally. Alluvial aquifers are spread over vast areas and water levels are less sensitive to abstraction. The amount you can extract doesn't vary with lowering of water level. 

People depending on hard rock aquifers experience the limitation of the resource yearly and are more willing to join cooperative initiatives to manage the resource.

I have just given a gist of the more elaborate arguments in the paper. The graphic below very neatly compares hard rock and alluvial aquifers. 

 Source: Pratik Kumar and Veena Srinivasan 2025

The paper is open access.

Plastic In Sediment, Antarctica Ice Core, Alfred Wallace

A few interesting readings:

1) Sedimentation Shifted - How rivers move sediment along their course to the sea is an important aspect of sedimentology research. Grain size, shape, and density, all affect how currents move sediment, and where and in what proportions sand, silt, and mud particles come to be deposited. Now there is a new kid on the block: plastic. Catherine Russell has written a fascinating article diving deep into experimental work on how plastic impacts sediment transport. The work she describes has important implications for our understanding of plastic pollution in rivers, and the role plastic particles plays in enhancing erosion rates and sediment redistribution in riverbeds. 

2) Antarctica: 1.2-Million-Year-Old Ice- Scientists use gases trapped in old ice to measure ancient atmospheric composition and estimate past climatic conditions. A long running drilling program in Antarctica had so far recovered 800,000 year old ice. That record has been recently broken. Scientists have reached the very bedrock of the Antarctica continent. The oldest ice at the very bottom is 1.2 million years old. This is the longest continuous record of our climate that we have so far.  It hold much valuable information on climate fluctuations through the Pleistocene and Holocene. This article is a press release of the University of Bern. 

3) Beyond Evolution: Alfred Russel Wallace’s critique of the 19th century world- Alfred Russel Wallace is the co-discover of evolution through natural selection along with Charles Darwin. He was a brilliant naturalist and made foundational contributions to natural history. But he also was very sympathetic to the plight of local people suffering under colonialism and the environmental degradation the race to strip the land of resources was causing. Marshall A. summarizes nicely Wallace's observations on the impact of environmental damage, both in his native Wales and also during his travels in the far away Malay archipelago. 

Let me take this opportunity to share again this lovingly crafted documentary on the life and work of Alfred Wallace. It is made as a paper-puppet animation, produced by Flora Litchman and Sharon Shattuck and narrated by George Beccaloni of the  Natural History Museum London and Andrew Berry of Harvard University.

 

What a fine example of science outreach. 

The Garden Of Ediacara

I came across this lovely evocative passage in Nick Lane's book Transformer: The Deep Chemistry of Life and Death.

"You are not completely spineless. You have a notochord: a flexible rod made of cartilage, which in your descendant, millions of generations hence, will develop into a proper backbone. For now, you flex your rod like an eel to undulate through the water, never quite fast enough. Better to stay submerged in the soft mud at the bottom, with only your head visible, while you filter out grains of food from the swell. You have a wormlike head, with a small bulging of nerves that will one day become your brain. Your eyes aren't much use, but at least you can make out the looming of a monster, and swiftly bury your head again. Oh, times have changed. Not long ago, the world was full of gently filter feeders, swaying their fronds softly in unison, never harming a soul. Not that you remember, except in some hazy instinctive yearning for the garden of Ediacara. But now there are vast armour-plated war machines, bristling with claws and spikes and rows upon rows of crystalline eye facets fixing you from every dimension. You are a tender morsel, barely a couple of inches long, protein-rich muscle strapped to a crispy rod; a tasty snack for Anomalocaris. Better pull in your head again, just in case- being a little bit spineless might help you survive in this fearsome new world, outnumbered a thousand to one by spiny monsters".

The passage describes the early Cambrian world (540-510 million years ago) which saw the rapid diversification of the animal biosphere. The ancestors of vertebrates had worm like bodies, and Anomalocaris, an early arthropod, was top predator. Much before, the garden of Ediacara was a very different place. Complex multicellular life appears in the fossil record from about 570 million years ago in the Ediacaran Period. These creatures were sessile (fixed to the sea floor) filter feeders with body shapes resembling large leaves and fronds. Evidence of mobile animals manifests by 550 million years ago. Their tracks, trails, and burrows are preserved in soft sediment.

The graphic shows this  'Edicaran biota', a term that includes a diverse and unrelated groups of organisms. Three distinct phases, termed Avalon, White Sea, and Nama,  showing different community assemblages and increasing ecologic specialization are recognizable through the Ediacaran Period. Notice that mobile bilateral creatures first appear in the White Sea (B) assemblage. 

 Source: Rebecca Eden, Andrea Manica, Emily G. Mitchell: Plos Biology 2022.

Later in the chapter Nick Lane elaborates on how many of these Ediacaran filter feeders, simpler creatures without specialized tissues for different functions,  could not cope with the anoxic sulpur rich environments and died out. Sponges notably did survive. Mobile animals though had evolved a rudimentary circulatory system and molecules like myoglobin and haemoglobin, capable of storing oxygen and removing carbon dioxide. When oxygen levels increased in the Cambrian their descendants had metabolic machinery to take advantage of this high-octane environment. The radiation of animals utterly transformed our world. 

I highly recommend this book. It has a fair bit of chemistry in it. Nick Lane explains much of it using easier to follow diagrams instead of the dreaded chemical equations of our college years. He is a firm advocate of the metabolism first (as against a RNA/genes first) view of the origin of life and provides elegant explanations of energy flow and the evolution of metabolic pathways that build organic molecules to form biomass and breaks them up to power respiration. Disease and ageing is the inevitable consequence of the eventual degradation of these metabolic reactions. 

At the heart of all this is the Kreb's cycle, a series of reactions which burn sugars in oxygen to generate energy for cellular functions. But the surprise is that much of life can get by with only a partial Kreb's cycle. In many microbes, it is not a cycle at all, but a short linear path. Not at all what our biochemistry book taught us and a lesson for creationists who insist that systems like the Kreb's Cycle are irreducible complex, a sign of intelligent design, which could not have evolved through incremental steps.

Nick Lane- Transformer: The Deep Chemistry of Life and Death.

Deep Sea Mining, Indian Ocean, Infectious Diseases

Some readings for you:

1) Mining the bottom of the sea: The deep sea bed is considered the last frontier on earth for mining. Large patches of the sea bed are littered with metallic lumps or nodules rich in manganese, cobalt, zinc, and nickel. These elements are considered vital for powering the world's green economy. Nauru, a tiny Pacific Ocean island nation situated northeast of Papau New Guinea, along with a Canadian mining company, wants to start mining a region of the Pacific between Hawaii and Mexico known as the Clarion-Clipperton Zone. Scientists warn that a hurried push to mine the deep ocean bed will result in an irreversible loss to biodiversity, ecologic functioning, and ocean health. Elizabeth Kolbert writes about the complex legal and regulatory issues and conflicts of interest related to international deep sea mining.

As things stand in June 2024, a deep sea mining code is still being decided by the International Sea Bed Authority. Rohini Krishnamurthy of Down to Earth has the latest news on the progress made on this issue. Negotiations are hampered by a lack of basic science and divergence of views between member states.

2) Indian Ocean headed for a near-permanent state of marine heat wave:  Rapid fossil fuel emissions over the past century or so has changed the earth's energy balance. More energy is now coming in than is being radiated out to space. More than 90% of this excess energy is ending up in the ocean as heat. As a result, the world's oceans are warming up. The Indian Ocean is warming rapidly too. Recent studies have found that it may be heading towards a scary sounding situation known as 'permanent heatwave state' where the sea surface temperatures exceed a threshold value for 220-250 days a year.

Environment and climate journalist Nidhi Jamwal summarizes the findings of this research and a new book titled The Indian Ocean and its Role in the Global Climate System. The consequences are far reaching, impacting tropical cyclones, biodiversity, and fisher folk livelihood.

3) Probing the pathogens that afflicted ancient humanity: Pathogens and humans have been co-evolving for millennia. Paleoanthropologist John Hawks charts out the history of some of the common infectious diseases afflicting humanity. Infection patterns are not random. Rather, they follow networks of transmission shaped by ecology and culture. Very illuminating essay!

Evolution Through Punctuated Equilibrium: History Of An Idea

Palaeontologist Niles Eldredge explains how one of the most famous papers on paleontology and evolution came to be published: 

Steve was determined to be a part of Tom’s plan to do a GSA symposium and publish a book of essays on this new-fangled concept of “paleobiology.” Tom had a list of topics and was shopping around for speakers to be assigned to each one. When Steve saw the list, he told me that he had first wanted “morphology”—but that was already assigned to Dave Raup. So he opted instead for “phylogeny”—but that had been grabbed up by Mike Ghiselin. That left only “speciation,” the last of the evolutionarily imbued topics on Tom’s list, as yet unassigned. Steve called me up, explained the situation, and said he had settled for speciation—but could not think of anything much to say about it beyond the manuscript I had written and recently submitted to Evolution—there of course being no Paleobiology as yet. “The Allopatric Model and Phylogeny in Paleozoic Invertebrates”—a distinctly un-Gouldian, plodding, if accurate, title (Eldredge 1971). Without Ralph Gordon Johnson in the editorial chair of Evolution at that time, I doubt that that early paper would have been accepted. As it was, it was likely to have gone relatively unnoticed—had not Tom come along, Steve grabbing “Speciation”—and Steve asking if we could coauthor the paper along the basic lines of my first effort. He was stuck with “speciation,” and couldn’t think of anything much to say beyond what I had said in the Allopatric Model manuscript.

This passage is from an article by Niles Eldredge titled Reflections On Punctuated Equilibria, published in a recent issue of Paleobiology. The 1972 paper he refers to, coauthored with Stephen Jay Gould, was, Punctuated equilibria: an alternative to phyletic gradualism. It marked the beginnings of a long debate on how to interpret the patterns of morphological change observed in the fossil record. Do species remain in stasis, showing little morphological change through much of their existence as Eldredge and Gould argued? Do periods of rapid morphological change coincide with the origin of new species (speciation)? Supporters hailed it as a revolutionary work. Critics called it 'evolution by jerks', a jibe aimed not just at the patterns of change.

Dr. Eldredge provides a very insightful look at the history of this idea including some fascinating snippets on Darwin's thinking about divergence and species origins. For Darwin, change accumulates incrementally over long passages of time. Divergence via natural selection can give rise to descendant varieties even without geographic isolation of a population. Later thinking has given more importance to exogenous factors like climate change in causing habitat fragmentation and reproductive isolation. Populations gets geographically isolated first, and then diverge from the ancestral species either through natural selection or random genetic drift. Eldredge and Gould applied this idea to the fossil record and emphasized that the sudden appearance of new fossil species is a manifestation of long periods of stability interrupted by episodes of isolation and geologically rapid shifts in morphology (allopatric speciation).

There is a lot to take in and think about the long term patterns of change preserved in the fossil record. But it is enriching reading. The article is open access.

Patterns Of Angiosperms And Insect Evolution

Charles Darwin famously called it an 'ábominable mystery'. He was referring to the sudden appearance and diversification of flowering plants in the Cretaceous fossil record. He noticed that these early fossils resembled modern flowering plants. 'Primitive' or ancestral stages were missing. Today, biologists categorize these as crown and stem representatives of a group. 

The first fossil evidence of flowering plants is from 140-130 million year old sediments. These are early types of pollen grains with one aperture (uniaperturate). Triaperturate pollen is found in slightly younger 125 million year old rocks. Towards the end of the early Cretaceous, by around 100 million years ago, flowers, leaves, and other organs appear from several continents representing all the major groups of angiosperms.

The picture below is of an early Cretaceous (~100 million year old) flowering plant from the lotus family. The location is northeast Brazil. There is a remarkable preservation of the whole plant, with connected roots, rhizome, leaves, and aggregate fruit. 

Source: William Vieira Gobo et.al. Nature Scientific Reports 2023- A new remarkable Early Cretaceous nelumbonaceous fossil bridges the gap between herbaceous aquatic and woody protealeans.

Taking a long view of their evolutionary pattern, angiosperm diversification is structured in three phases. The first phase was a steady expansion through early to late Cretaceous. There was more rapid diversification in late Cretaceous by around 70 million years ago. Enumeration of floral species through the Cretaceous indicate that angiosperms made up about 5% of species in early Cretaceous, increasing to 80% by Maastrichtian times (late Cretaceous). Despite this increase in species numbers, in terms of biomass, angiosperms were still a small component of Cretaceous floras. Their domination of floral communities, including the origin of modern wet tropical forests, began in the Paleogene (65-24 million years ago) after the end Cretaceous mass extinction. Michael J. Benton, Peter Wilf, and Herve Sauquet have provided a good overview in New Phytologist of this pivotal phase of ecosystem change.

These evolutionary changes did not occur in isolation. Throughout the Cretaceous, significant changes were occurring to terrestrial ecosystems, with the origination of many plant and animal groups. This extended phase of ecosystem reorganization is known as the Cretaceous Terrestrial Revolution. Angiosperm diversification is thought to have played a key role in this transformation of land biodiversity, so much so, that the phase from about 100 million years to 50 million years ago is known as the Angiosperm Terrestrial Revolution.

The Cretaceous -Paleogene mass extinction hit angiosperms hard, as well as altering the trajectory of their evolution. For example, there was a 40% loss of diversity of flowering plants in Colombia following the mass extinction. But certain attributes of angiosperms, such as their partnerships with other organisms, their ability to efficiently capture energy and enhance photosynthetic rates, and an underlying genetic propensity to speciate, resulted in them expanding rapidly in the post extinction landscape. Angiosperm evolution opened up opportunities for a variety of land creatures including insects, spiders, lizards, birds, and mammals,  eventually driving up terrestrial biodiversity to 10 times more as marine biodiversity.

Paleobiologists are interested in understanding the interaction and impact angiosperm diversification could have had on other groups of plants and animals. Of particular interest is the diversification of insects in the Cretaceous and Paleogene.

Modern insect lineages began diversifying by 245 million years ago, long before angiosperms evolved. Gymnosperm and insect communities preserved in amber and sediments show that insects had an intricate relationship with host gymnosperms like cycads, conifers and ginkgoaleans.  Insect pollination of gymnosperms predated the origin of angiosperms by at least 100 million years and their fossil record show phases of diversification even when angiosperms were rare. 

Did angiosperm evolution also drive a rise in insect diversity? Pollinator insects particularly would seem to benefit from an abundance in flowering plants, and if so, what co-evolutionary patterns are apparent from the fossil record?

David Perise and Fabien Condamine have tackled this question in a new study in Nature Communications. I will share this beautifully compiled infographic from the paper that conveys so clearly the patterns of angiosperm and insect diversification through the Cretaceous and Cenozoic.

Digging into published databases, the researchers compiled data on the origination and extinction times of angiosperm and insect families. They then statistically analyzed whether angiosperm and insect origination and extinction times, and pulses of their diversification coincide. Their analysis showed that angiosperms seemed to have played a dual role in insect evolution. They mitigated insect extinction through the Cretaceous and spurred on the origination of new insect groups in the Cenozoic. Besides a broad analysis of insects, they also found that pollinator insects like bees and long proboscid butterflies show a pronounced diversification alongside angiosperm lineages. 

The success of angiosperms in the late Cretaceous and Cenozoic coincided with the decline in gymnosperms. Intrinsic mechanisms of genomic rearrangements in angiosperms resulted in repeated evolution of novel traits and specializations. They competitively displaced gymnosperms. The impact on gymnosperm dependent insects was variable. Generalist insect pollinators such as several beetle lineages transitioned to angiosperms. Much of the co-diversification of angiosperm and insects can be explained by this shift of gymnosperm pollinators to angiosperm hosts.  Gymnosperm specialized insect groups did not fare that well. For example, gymnosperms like Cheirolepidiaceae and Bennettitales went extinct by the latest Cretaceous. This was followed by the extinction of insect groups that were dependent on these plants such as some specialized long-proboscid flies, scorpionflies and lacewings.

Insect diversification did not depend only on angiosperms. Analysis also shows that warmer climate phases negatively impacted insect diversity and coincided with higher insect extinction rates. There seems also to be a relationship with other plant types. Spore plant and gymnosperm diversity had a positive impact on origination rates of insects. Ecosystem relationships and dependencies are multifarious and complex as this analysis between angiosperm and insect co-evolution shows.

Darwin's anxiety over flowering plants reflected his insistence that evolution is gradual. Nature does not make leaps, he stressed. He explained abruptness in the fossil record by invoking missing strata due to non deposition and erosion. Regarding flowering plants, he suggested that fossils were perhaps preceded by a period of cryptic evolution of that lineage that took place in a remote area or a lost continent, although he conceded that this was a poor explanation. However, this latter view, that a substantial lag time or a long fuse precedes the bang, continues to resonate among many biologists. Molecular methods that compares accumulated genetic difference to calculate the time of divergence of groups indicate a fairly long gap between the genetic branching of lineages and their first fossil appearance. 

Most familiar is the example of the origin of animals. Molecular data indicate that animals originated by 750 million years ago, yet unequivocal animal fossils appear by 570 million years ago, close to 200 million years later. Similarly, some molecular estimates put angiosperm origins to pre-Cretaceous times, stretching back 240-200 million years ago to Triassic-Jurassic, a good 100 million to 60 million years before first appearance of fossils.

This idea of a phylogenetic fuse has been recently criticized. Published in Systematic Biology, Graham E. Budd and Richard P. Mann have undertaken a critical examination of molecular clock methods. Their analysis indicate that popular methods used to assign probabilities to maximum age of lineages are biased against rapid lineage radiations being true evolutionary events. In their view, the mismatch between molecular dates of lineage origin and the timing of the first appearance of their fossils is an artifact. They point out that the coincident appearance of fossils from widespread localities in a particular sequence and across different modes of preservation faithfully records evolution. The time gap between the origin and later diversification of lineages is not that deep.

The 'abominable mystery' of the sudden appearance of fossil groups may in fact be a real biological motif in earth history, signalling the rapid radiation of lineages filling ecologic spaces following an environmental crises and evolutionary innovation.