Ganga Earthquake, Nile, Deep Sea Habitats

Some readings over the past few weeks:

1) An Earthquake Changed the Course of the Ganges. Could It Happen Again?  Sediment load carried by big rivers like the Ganga often choke up channels and force the river to cut another path. Sudden channel shifts can also occur due to tectonic movements. A recent survey of the Ganga about 100 km south of Dhaka, Bangladesh , identified an old channel of the Ganga. Exploring this area, researchers came across veins of sand cutting across the sediment layers. These veins or sand dikes were  injected into the surrounding sediment. They are a sign of major ground trembling triggered by a large earthquake. Ground motion may pressurize buried sand and inject it  upwards. Further studies showed that this event may have been a 7-8 magnitude earthquake that occurred 2500 years ago. Kevin Krajick writes about this discovery and the larger geologic context.

2)  Lessons from the Nile about rivers and society. The Nile river has sustained agriculture, human habitation, and royal dynasties for millennia. A Nature Geoscience editorial summarizes a collection of sedimentological and geomorphologic studies that track the evolution of the Nile through the Holocene. Phases of the river cutting a deep valley changed to phases of the river flooding laterally and building fertile floodplains. This geomorphological evolution driven by climate change and more recent dam building have influenced agriculture and social systems in the past as well as the present. 

3) Ocean Exploration: Meet The Deep. I highly recommend this site. National Ocean and Atmospheric Administration, U.S.A., has compiled some stunning photographs and videos of deep sea habitats and the diverse forms of life that inhabit this little understood world. Corals, sponges, brittle stars, molluscs, worm tubes- attached to the bottom, living around energy sources such as hydrothermal vents and cold seeps. It is an absolutely fascinating exploration of the biodiversity of the deep sea. 

Octocoral and Brittle Star: Source NOAA Ocean Exploration

As a bonus, these images make great wallpaper for your mobile phone!

Field Photo: Unusual Himalaya Metamorphic Rock

My friend Emmanuel Theophilus, who spends a lot of time wandering in the high Kumaon Himalaya, sent me this photo of a feldspar rich gneiss.,

He observed this loose boulder near the small settlement of Bugdiyar in the Goriganga valley, north of Munsiyari town. Bugdiyar is located in the Greater Himalaya. This is a high grade metamorphic rock terrain. As you walk along the many trails that lead to places like Nandadevi Base Camp and Milam Glacier,  you can observe mica and amphibole rich schist with gleaming garnets, quartz and feldspar rich gneiss, migmatite gneiss (partially melted gneiss), and leucogranite (quartz and feldspar rich magma) intruding this high grade ensemble. 

This traverse takes you into the core of the Himalaya orogen, where high temperature and pressure during mountain building that took place 35 to 15 million years ago transformed the sedimentary protolith into metamorphic rocks. 

This particular gneiss rock has an extraordinary texture. I have never before seen such large feldspar (white crystals) in a metamorphic rock. Judging by the pebbles and other rocks strewn by the side, these are inches long feldspar grains. 

I want to introduce two terms used to describe texture in metamorphic rocks; porphyroblastic and porphyroclastic. Both these terms describe rocks with very large crystals surrounded by fine grained minerals. These are rocks with two distinct crystal size classes. 

Porphyroblastic texture forms when one mineral grows more quickly than other minerals during metamorphism. Large crystals of the rapidly growing mineral are set in a finer crystalline matrix. Both the large and small sized minerals have recrystallized, but at different rates.  

In contrast, porphyroclastic texture forms when there is a size reduction of some minerals , leaving one unaffected mineral larger than the rest. This situation occurs most commonly in fault zones where softer minerals may get crushed more easily leaving the resistant mineral as a large porphyroclast. These types of rocks have a broken appearance. The softer minerals become aligned to give the rock a prominent streaky banded texture. The more competent mineral may also develop an elongated shape.

Which of the above is the rock Theo found? My guess is that it is a porphyroblastic gneiss. Take a closer look at the beautiful large grains. They seem to be the result of growth during metamorphism, in the process engulfing small pockets of mica in their interiors. The rock lacks the streakiness and the often broken, bent, and stretched large grains characteristic of a porphyroclastic texture.

However, there is a subtle sign of deformation too. Have a look at this close up. 

The black arrows point to rugby ball shaped feldspar grains. They have a long axis and a short axis and appear to be stretched in one direction. Also notice the grey cracks running along the longer axis of many of these crystals and continuing into the rock. These are paper thin zones where force or stress was localized. The change in shape (strain) in the feldspar grains follows these very narrow zones of deformation. 

All of the above is my reasoned speculation on the origin of this texture. The next step is to meet up with Theo near Bugdiyar and walk along the Goriganga in search of the outcrop.

The Goriganga near Bugdiyar. It is spectacular out there!

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.

Remotely India: Chittagong Tripura Fold Belt

Remotely India #13

Did you know that the easternmost part of the Bengal delta is being compressed into folded hill ranges? These go by the name Chittagong Tripura Fold Belt (CTFB), also referred to by geologists as the Outer Indo Burman (Myanmar) Ranges.

Take a look at the annotated satellite image below. The CTFB appears as a series of north south oriented ridges and valleys, extending from northern Tripura to south of Cox Bazaar in Bangladesh. 

Structurally they are made up of strata folded into anticlines (upwarps) and synclines (downwarps). To the east, they are separated from the inner Indo Burman (Myanmar) Ranges (IBR) by the north south trending Kaladan Fault. The Chittagong Coastal Fault marks the westernmost boundary of this fold belt, although the sedimentary pile below the sea bed of the Bay of Bengal to the west is also deforming. The 'deformation front' of this terrain is therefore further to the west of the Coastal Fault. 

As you might have guessed, these fold belts are a result of the Indian tectonic plate converging with Asia. But the nature of tectonic plate interaction is different from the plate collision that formed the Himalaya. In the case of the Himalaya, the continental crust of the Indian plate has collided with the continental crust of the Asia plate. The lower part of the Indian continental crust has slid under Tibet while thick slices of the Indian upper crust have been thrust up by faults to form the different geologic units of the Himalaya. 

Tracing the mountain arc southwards from its bend around Arunachal Pradesh, a different type of tectonic plate interaction is unfolding. In the Himalaya collision zone the more buoyant continental crust is sliding at a shallow angle underneath Tibet, a process known as underplating. In contrast, the Indian tectonic plate along this eastern convergence zone is made up of denser oceanic crust. As a result, along the zone of contact with Asia, this dense plate is subducting or taking a deep dive at a steeper angle into the mantle. 

Another difference apparent from the surface structure is the presence of both vertical and sideways movement of crustal blocks. This occurs because the Indian plate is pressing into Asia at an angle. Oblique convergence results in thrust faulting wherein rocks are moved up along east sloping fault planes. Collision at an angle also causes blocks to slide past each other along strike slip faults.  

The IBR is an older mountain chain formed by the subduction of the Tethyan oceanic crust underneath the Asia plate and the smaller Myanmar plate. This process, initiated in the Late Cretaceous around 100 million  years ago, eventually led to the formation of a complex fold belt by mid Miocene times (15-20 million years ago). 

This fold belt is made up of deep sea sediments and fragments of the Tethyan oceanic plate. These rocks were subjected to very high pressures during mountain building. Sheared and fractured rock units occur in a melange made up of dismembered blocks of varied rock types juxtaposed by faults. Heat and high pressure acting on rocks rich in aluminum, calcium, iron, titanium, and magnesium has resulted in the formation of deposits of exquisite gemstones such as jade, rubies, sapphires, spinel, and peridote. The IBR is studded with precious stones!

By Miocene (~20 million  years ago) the IBR had emerged above sea level as elevated ranges and had started eroding. Sediments shed from these hills were deposited in delta and shallow marine environments of the Bengal Basin to the west. During continued subduction of the Indian plate, between 2-4 million  years ago, this thin skin of the crust made up of about 5 km of sediment was scraped off, faulted, and crumpled up to form the CTFB. Geologists call these scraped off wedges of sediments that form along subduction zones as 'áccretionary prisms'. 

Further to the south, the Andaman Islands is also an accretionary prism formed along the plate junction between India and Asia.

The deformation of the CFTB diminishes from the east to the west. There are two distinct structural domains of this belt. To the east is a more tightly folded belt known as the Eastern Highly Compressed Fold Thrust Zone. Towards the west, is the more open Western Fold Thrust Zone. The emergent part of this fold belt is bounded to the west by the Chittagong Coastal Fault. However, geophysical studies show that the strata below the Bay of Bengal sea bed is also being warped and can be considered part of a westward growing CTFB.

The annotated satellite image below is a close up of the CTFB and the IBR. The black line is the Kaladan Fault separating the two, but even without my annotation, the two terrains have a distinctly different appearance. The older IBR have been more deeply dissected by streams. They have an etched faceted texture. To the west, the younger ranges of the CTFB have a more uniform even texture. 

Finally, I just wanted to put up a structural cross section of the CTFB. The folded and faulted nature of the sedimentary strata is apparent, as is the difference between the more tightly folded eastern zone compared with the more open western domain. Source: Md. Sakawat Hossian et.al. 2022: Lithosphere.

Scientists study terrains like the Chittagong Tripura Fold Belt to understand the mechanical response of the crust to different types of tectonic plate interactions. There is an economic incentive too. The IBR with its precious stone deposits has long been a target of exploration. In the CTFB natural gas seepage has been observed at many places. Geologists are interested in understanding the subsurface structure to target search for hydrocarbon accumulations.

As always, exploring Indian geology from satellite imagery is fun and a great learning experience for me. Stay tuned for more such stories!

Links: Europa Life, Moon Geology, Citizen Activism

Some readings I perused over the past couple of weeks.

1) Our picture of habitability on Europa, a top contender for hosting life, is changing. Jupiter's moon Europa has long been a contender for hosting life. But lately some scientists have expressed their doubts. Europa has an ocean beneath a 20 km icy crust. Geologists now think that the sea floor is not active. They simulated conditions which could generate shallow earthquakes leading to fault movement and exhumation of fresh rock. Reaction of sea water and freshly exposed rocks is necessary for chemical reactions that sustain life. Results suggest an inert sea floor. Another study implied no magmatism on Europa. Rising magma brings with it heat and chemicals. But, could these be transient conditions that we have caught? Maybe there is a cyclicity to Europa's energy flow. Some interesting thoughts in this article.

2) China's Moon atlas is the most detailed ever made. The Chinese Academy of Sciences has released a stunning 1:250,000 scale geologic map of the moon. A decade of research has revealed 17 rock types ( I used to think only basalt!), 81 basins, and 12,000 odd craters! Compiled from orbiting satellites and then sharpened using data from the two lander missions.

3) How Punekars fought for their hill, Vetal Tekdi, to save its ecology. My city Pune has a proud tradition of citizen activism. For the past few years citizens have vigorously protested a road planned along a forested hill slope. This hill has been a life saver for thousands of citizens as a recreation spot. It hosts rich biodiversity and is an important groundwater recharge zone. The Pune Municipal Corporation is insisting on building this road, despite their own reports admitting an adverse environmental impact, and pointing to at best a short term marginal improvement in traffic flow. The fight to save the hill goes back a couple of decades. Shobha Surin has done a good job summarizing this long battle in Question of Cities.   

Geological Contacts: Angular Unconformity Kaladgi Basin

 Remotely India Series #12

Through the Proterozoic Eon, beginning around 2 billion years ago,  extensional forces acting on continental crust opened up several sedimentary basins across what is now peninsular India. Crustal blocks subsided along faults and these depressions filled in with sediments deposited in fluvial and shallow marine environments. These basins were long lived, some lasting for more than a billion years. 

Sedimentation was not continuous.  Pulses of sediment deposition were punctuated by long periods of non deposition. Tectonic movements deformed early deposited piles of sediment. They were uplifted and an extensive basin wide erosional surface formed.

There was then a renewed phase of basin development. Sediment of these successor basins were deposited on tilted and folded older strata. Commonly, these younger packages of sediments are relatively undeformed. They are preserved as mesas and plateaus made up of flat lying strata. This discordance in attitude between two sets of strata separated by a widespread erosion surface is known as an angular unconformity.

In this post I will highlight an angular unconformity from the Kaladgi Basin from north Karnataka, south India. I have used high resolution imagery from Indian Space Research Organization's Cartosat.  Imagery is available for browsing and download from ISRO's Bhuvan 2D web maps.

The first image shows the area around Ramdurg village. The multi-stage history of the basin is readily apparent. The light colored strata exposed along narrow ridges are folded, while the rust brown hills are made up of undeformed sediments. The light toned strata are quartzites of the Bagalkot Group. The brown sandstone which rest on the Bagalkot quartzites are the Badami Group. Standard annotations show the varying dip and strike of the folded Bagalkot sediments. The white cross in grey circle denotes horizontal Badami strata. 

Kaladgi Basin history has become clearer based on recent geochronologic work by Shilpa Patil Pillai, Kanchan Pande, and Vivek S.Kale. They infer that basin initiation occurred around 1.4 billion years ago. Sedimentation of the Bagalkot Group terminated by 1.2 billion years ago. Movement along major WNW-ESE and tranverse NNE-SSE to NE-SW trending faults deformed the Bagalkot sediments into a series of folds around 1.1 billion years ago. This was followed by uplift and erosion of these folded sediments. Deformation was accompanied by low grade metamorphism of these rocks.

The basin floor subsided again around 900 million years ago initiating deposition of the Badami Group of sediments. The famous cave temples of Badami have been cut out from the lower part of the Badami sedimentary sequence.

The next imagery is a good example on how to recognize the relative timing of deformation events. Arrows point to fracture sets in the Bagalkot quartzites. These lineaments do not extend into the Badami sediments implying that fracturing occurred during an earlier phase of deformation. 

Let's look at a location that shows the angular discordance between the Bagalkot and Badami sediments. This is near Shirur town, north of Badami.  The lighter toned steeply tilted Bagalkot sediments outcrop as E-W trending narrow ribbons, north of Budanagad village. The brown colored Badami sediments form a more extensive plateau. Since these strata are horizontal, the traces of bedding planes form concentric bands mimicking contour lines. 

The final location is just south of Ramdurg village. The unconformity here is a little harder to decipher, but you can make out the tilt of the light colored Bagalkot quartzites, annotated by the standard notation of strike and dip. The quartzites form triangular facets sloping eastwards. Like the previous example, the concentric bands of brown in the adjacent hill indicates that this is the overlying horizontally disposed Badami sandstone.

Many Proterozoic basins of India contain such unconformity bounded sequences. Some more classic examples come from the Chattisgarh, Cuddapah, and Vindhyan basins. These sequences from different basins were not deposited synchronously. Each basin has it own trajectory of sedimentation, deformation, and erosion. 

Detailed field mapping, supplemented by absolute dating of rocks wherever possible, is elucidating the complex poly-phase history of Indian Proterozoic sedimentary basins in the context of global continental breakup and reassembly. For arm chair geologists and enthusiasts, easily available web mapping technology makes it possible to join in the excitement of teasing out these terrain's many secrets hiding in plain sight.

Links: Earthquake Detectives, Origin Of Life, India Water Act

Reading from the past few weeks- 

1) How earthquake scientists solved the mystery of the last “Big One” in the Pacific Northwest. The American northwest is a tectonically active region. About 150 km west of the Pacific coast is the Cascadia subduction zone. Here, the Juan de Fuca, Explorer, and Gorda tectonic plates slide underneath the continental plate of North America. Large earthquakes have occurred in the past and will occur in the future. 

Reporter Gregor Craige has written a book, On Borrowed Time: North America’s Next Big Quake, in which he explores the region's earthquake potential and the cross disciplinary studies that enable scientists to understand past earthquake history as well as the impact a big future earthquake will have. Canadian Geographic has shared an abstract from his book. The earthquake puzzle was solved by combining information from tree rings, Native American peoples memories of past events, and Japanese record of tsunamis. It is fascinating reading. 

2) To unravel the origin of life, treat findings as pieces of a bigger puzzle. Was life's beginnings in a warm little pond or in a deep sea hydrothermal vent? Did lightning provide the energy, did asteroids provide the organic matter? There are many many scenarios that try to provide an explanation to this vexing question. 

One of the leading researchers of this field, Nick Lane, and his colleague Joana Xavier, have summarized some of the key arguments and problems of the field in this tour de force of science writing. Highly recommended! 

3) Analysis: The Great Indian Water Act Of 2024. In more good news for industries, factories and foreign investors, yet another Indian environmental law has been diluted to facilitate “ease of business”. Shailendra Yashwant begins his analysis of The Water Amendment (Pollution and Prevention) Act, 2024 Bill on this depressing note. Amendments seek to "rationalize criminal provisions". Polluters can now escape jail time and get away by just paying a fine. All this when climate change and water security is one of the big challenges facing India. 

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.

Is It A Lava Tube?

My latest field geology video is about a small cave in the basalt lava near my house in Pune city. The location is Hanuman tekdi, also known as Fergusson College Hill. The cave is along the slope right behind IMDR canteen. 

Is the cave a remnant of a lava tube, or has it formed by some other process? 

Sound on. Permanent Link - Fergusson College Hill Cave.

You can access this cave by walking along the path starting from the main gate of Gokhale Institute of Politics and Economics. Turn left as you approach the hill and after a few steps look up to the right. 

Visit quickly. As you can see from this photo, rubble from the construction works of water tanks at the top of the slope is slowly spreading and might cover up this cave. I hope not. 

More geology videos soon!

Deep Pacific Upside Down Waterfall

This passage from Helen Czerski's Blue Machine: How The Ocean Shapes Our World gives us a glimpse of the wondrous undersea universe we are just beginning to explore.

"We see upside-down waterfalls, she says. I don't understand what she means at first, and it takes me a few seconds to process the video as Deb keep talking. In those vertical chimneys, the walls crack and hydrothermal fluids come leaking out and  you get something that looks like half a toadstool growing out of a tree in an old growth forest. And suddenly I see it. This is a gigantic hydrothermal chimney looming out of the darkness, and hot water is indeed leaking out of its side. But because hot water is less dense than cold water, the hot water keeps flowing rapidly upwards. When it first hits cold water, its clearly dumped some minerals and made a ledge that sticks out- that's the toadstool shape that Deb is referring to. The water flowing upwards has had to flow outwards underneath the ledge before it can carry on upwards. But the ledge has developed a hollow on its underside like an upside-down bowl, so there is a pool of hot water there, held in the hollow as if it were filling up the inside of an umbrella. The boundary between hot and cold water shimmers like a mirror. And then the hot water is spilling out of its hollow and continuing upwards into the gloom. It really is an upside down waterfall".

Helen Czerski is watching this footage captured by a remotely operated vehicle exploring the area around the Juan de  Fuca Ridge, an undersea mountain chain a few hundred kilometers west of Seattle. Here, the Pacific and the Juan de Fuca tectonic plates diverge. Scientists are closely monitoring this ridge for seismic and volcanic activity, using a network of sensors  called the Regional Cabled Array. Deb Kelly is the Director of this project. Hydrothermal chimneys are sulfide and carbonate mineral deposits that form when hot mineral saturated sea water emerges through cracks in the ocean crust. The are common near mid oceanic ridges where the interaction of sea water and rock heated up by magma generates vigorous hydrothermal systems.

I'm only a quarter into this book and am enjoying every page of it. Highly recommended!

Kenjalgad Perched Aquifer

I have been experimenting with shooting videos of geological features with an accompanying commentary. Here are two of my recent efforts.

Last month I visited Kenjalgad, a small fort near the town of Bhor. As is typical of forts of the Sahaydri ranges, it sits atop a thick basalt scarp. 

The videos explain the geological conditions for the formation of a perched aquifer. I hope I have been clear in my explanation. Sound on please! 

Kenjalgad aquifer. Location 1- Permanent Link

Kenjalgal aquifer. Location 2- Permanent Link

Kenjalgad as seen in this picture is quite an impressive mesa.

The aquifer I described in the video occurs within the topmost rock layers of the scarp forming basalt. They form discrete accumulations of groundwater high up on these ridges, separate from the aquifers underlying the surrounding valley.

I am planning on making more of these videos of various geologic features. Should they be a little longer, say two or three minutes each? I would appreciate some feedback from you.

The Making Of Iceland

Committees are underappreciated. 

xkcd comics.

Happy New Year everyone!