Monday, September 16, 2019

Darwin: Citizen Science

After his return to England in 1836 from a five year round the world trip aboard the Beagle, Darwin did not travel again for any extended fieldwork. His home became his study and his laboratory, but he was no lonely isolated genius. His ideas stemmed from data that streamed in from all over the world.

From Darwin: The Life of a Tormented Evolutionist

Down House had become the hub of a correspondence network across the Empire, its tentacles touching every little England. The sack of mail brought gems daily to aid his sexual selection. Botanists from Ceylon to Calcutta sent reports on monkey manes and bearded Indians; mining engineers from Malacca to Nicaragua told of indigenous customs; tile manufacturers in Gibraltar attended to merino lambs; wine exporters in Portugal followed the local tailless dogs; Laplanders measured reindeer horns; New Zealanders heroically tackled the Maori's sense of beauty; and missionaries and magistrates from Queensland to Victoria ceased converting and incarcerating to observe aboriginal ways- with an old Beagle shipmate Philip King helping out. This is what Darwin excelled at: collecting and collating, tracking down facts, verifying,extending his old notebook speculations to embrace the globe.

Darwin had many India connections. His botanist friend Joseph Hooker who had traveled to India in the 1840's had been one source of information on indigenous plants, animals, and people. From 1855 or so, Edward Blyth, curator of the museum of the Royal Asiatic Society in Calcutta became his chief contact. He struck up a lively correspondence with Darwin. Details about monkey manes and bearded Indians would have come from him.

"his large and varied stories of knowledge, I should value more than that of almost anyone" he wrote of Blyth.

Vikram Doctor has written an insightful essay on Edward Blyth's life. It sketches the sharp contrast between the financially comfortable life Darwin lived in England against the hardscrabble existence of Blyth, who managed to stay on for 21 years in India on a salary of Rs 250 a month, supplementing it with a trade in exotic birds and animals.

A love for natural history drove Blyth on and Darwin benefited from that immensely.

Tuesday, September 10, 2019

Books: Timefulness And A New History Of Life

More books arrived in my mailbox.

I have been looking for an updated sweeping history of life survey. Peter Ward and Joe Kirschvink have written just that book, covering topics from the origin of life to mammalian evolution. I'm in the middle of the section on the origin of life, along which I am re-reading the relevant section from Nick Lane's superb book The Vital Question. Flipping ahead, I can see that the authors have developed broad narratives of how ecosystems changed, framed within the themes of catastrophic events and changes in levels of oxygen, carbon dioxide and hydrogen sulphide (very early in the history of life).

After enjoying her first book, Reading the Rocks, I had to order Timefulness, a long essay on the need to be aware of the multiple time scales on which geologic processes operate. Marcia Bjornerud stresses that inculcating time-literacy is vital for a sensible societal response to our epoch of rapid planetary change.

I'll be sharing excerpts from time to time.

Saturday, August 31, 2019

Hot Water Springs Of Konkan- Geological Significance

During my recent trip to Konkan, just north of the Tural area, I came across a sign for a hot water spring.

This is located in the small settlement of Aaravali. The area around the spring has been converted into a tourist spot where locals and tourists come to enjoy a warm bath.

One interesting feature of Konkan coastal belt is the presence of hot water springs arranged in a fairly narrow linear belt from north of Mumbai to Ratnagiri area in the south. They occur somewhat midway between the Western Ghat Escarpment and the coast. Few names from north to south- Vajreshwari, Akoli kund, Ganeshpuri, Pali, Dasgaon, Unhere, Tural, Aaravali, Rajapur. Satellite image shows the area between Dabhol and Ratnagiri. Hot springs are located within the oval. The dark brown undulating line is the trace of the Western Ghat Escarpment.

What is so special about this area? See the map. Black lines are fracture zones, trending N-S, NW-SE and NE-SW. Hot water springs are located in the vicinity of these fractures roughly within the oval. The depicted area is again between Dabhol and Ratnagiri, but this relationship between fracture systems and location of hot springs applies elsewhere along the entire Konkan coastal region.

Source: Neotectonism in the Indian Subcontinent: Landscape Evolution- K.S Valdiya and Jaishri Sanwal (modified).

Water temperatures are between 50 deg C to 60 deg C. Interestingly, analysis shows significant levels of radon gas at measured sites near Tural. Presence of radon gas hints at the reason why there are hot springs here. It points to deep circulation of water.

The crust in this region is made up of a foundation of older Precambrian age granitic rocks overlain by several hundred meters of younger basalt of Late Cretaceous to Paleocene age (67-65 million years old). Radon forms by radioactive decay of uranium. The Deccan Basalts contain only tiny amounts of uranium. Granites on the other hand are enriched in uranium. Radon emission here imply that these fractures cut through the basalt pile and penetrate the 2 billion years and older granitic rocks underlying these basalts. 

Such fracture systems have provided a passageway for groundwater to percolate to great depths. Cool water comes in contact with hot rocks deep below and gets heated. This warmer buoyant water then rises to the surface, forming a hydrothermal circulation system. The cross section shows fracture/fault systems of the coastal region cutting across basalts and penetrating the underlying granitic basement. I have added a few additional fractures to the figure.

What makes the rocks hot? What is the source of heat?  Deccan volcanism ended 60 million yrs ago. It is unlikely that there is any magma underneath to provide heat. Rocks get hotter at depths due to the natural geothermal gradient. Some geologists think that many of these fractures are actually faults along which there is intermittent movement of the crust. This faulting may be causing friction between crustal blocks, generating additional heat in these zones. These fractures and faults are a legacy of the breakup of the India with Madagascar and later Seychelles during and post Deccan volcanism  68 -60 million years ago. This rifting of the Indian crust resulting in oriented fracture systems.

The schematic shows the evolution of the Western Ghat escarpment and the coastal region. Earlier, perhaps soon after Deccan volcanism ended, the escarpment was a west facing cliff formed when faulting caused the western block to subside . Subsequent erosion has resulted in this cliff retreating eastwards, creating a coastal plain. Orange lines mark the highly fractured Indian crust.

Source:  Western Ghat: The Great Escarpment of India- V.S. Kale 2010. (modified)

Next time you visit Konkan and take a dip in the invigorating warm waters, remember that grand geological forces of continental separation are responsible for the high heat flow and the ground water circulation systems that arise consequently.

Wednesday, August 21, 2019

Does Volcanism Cause Global Warming Or Cooling?

On million year time scales, does volcanism cause global warming or cooling?

The answer is both, depending upon the longevity of the volcanism and it effluents. Prolonged volcanic emissions over tens of thousands to millions of years of greenhouse gas carbon dioxide will warm the earth's surface. But magmatism and volcanism creates continental crust. During volcanic episodes and after the magmatic system dies, this new crust consumes carbon dioxide in chemical weathering reactions. This draw down of atmospheric carbon dioxide can result in global cooling, as is inferred to have resulted in the Cenozoic beginning around 30 million years ago, after collision of the India -Eurasian plates. Volcanism and tectonic activity can both warm and cool the earth's surface as magmatic arc systems grow and die.

Volcanism also ejects sulfur particles into the atmosphere. These particles block and reflect sunlight away and this albedo effect may result in cooling of the earth's surface. Volcanic ash falling on both land and sea may act as a fertilizer, enhancing organic productivity and further drawing down and sequestering carbon dioxide through increased organic carbon burial. A recent paper published in Geology by Gerilyn Soreghan and colleagues (open access) points to a temporal coincidence between explosive eruptions and glacial conditions during the Late Paleozoic. The researchers suggest that the prolonged icehouse conditions from around 360 million years ago to 260 million years ago resulted from explosive volcanism and effects of sulfate aerosols.

This paper has prompted a thoughtful commentary (open access) by Rice University geologists Cin-Ty Lee and Sylvia Dee on the broader controls of volcanism and crustal weathering on global climate. On the particular question of whether the Late Paleozoic ice age was a result of sulfate ejections, they differ somewhat from the authors of the study. Cin-Ty Lee and Sylvia Dee point out that the residence time of sulfur particles in the atmosphere is just a few years. To maintain a global icehouse for a 100 million year period would require large explosive eruptions every few years over tens of millions of years.

They point to an example of another period of enhanced magmatic activity in the Cretaceous Period. Field evidence from the continental interior of the U.S. shows just about 200 eruptions over a 10 million year period. Only a few of these were large enough to have ejected significant amounts of aerosols into the stratosphere. That is not to say that sulfate aerosol albedo cannot cool the planet. But it may happen over shorter 1000-10,000 year time scales. In case of the Late Paleozoic icehouse, they suggest that the pattern of cooling may hint at the causative factor. Numerous short-lived cooling events would be suggestive of explosive volcanism as the cause.

On longer time scales carbon dioxide will play a larger role in modulating climate. Explosive eruptions and resulting sulfate particle emissions are only a small component of magmatic flux. On the other hand, CO2 degassing is taking place even without eruptive activity. Long lived magmatic activity will result in a warming trend due to an increase in atmospheric CO2.  Post magmatism, a drop in atmospheric CO2 levels and cooling due to silicate weathering also takes place on longer million year time scales.

An extract from Cin-Ty Lee and Sylvia Dee commentary:

More broadly, the nature by which volatiles are exchanged between planetary interiors and their surfaces is rich with complexity. The magnitude and style of magmatism not only controls volatile degassing but also erosion, weathering, radiative balance, and biological productivity. How magmatic processes change through time and with geodynamic states is an area ripe for interdisciplinary research and new discoveries. Soreghan et al.’s work is an example of how investigating these processes from deep time to the present, as well as on Earth and other planets, will force us to rethink how planetary systems operate.

The geologic record shows that enhanced phases of volcanic activity sustained over thousands of years can cause the earth's climate to tilt towards a long lasting greenhouse or an icehouse. People who claim that the warming of the earth's surface over the past few decades is due to natural causes like volcanic eruptions and not fossil fuel burning must understand the time scales and amounts involved. Even big volcanic eruptions that occur every few years emit only a few million tons of CO2. Awkwardly, for anthropogenic warming deniers, these eruptive events may result in a short term cooling phase due to the effects of sulfate aerosols. A recent survey puts the total global emissions due to volcanic eruptions and non-eruptive degassing of magma to be about 0.3 billion tons per year. In contrast, human activity is putting 30-40 billion tons of CO2 in the atmosphere every year.

Explosive volcanism as a key driver of the late Paleozoic ice age.
Does volcanism cause warming or Cooling?

Saturday, August 17, 2019

Darwin: Victorian Menage A Trois

In 1864, a few years after the publication of the Origin of Species, Darwin, fighting a bout of illness took up some botanical work on Lythrum, a genus of flowering plants known as loosestrifes. He had been breeding them on and off for many years. His interest was in their sexuality as they gave him a deeper understanding on the evolution of sterility and reproductive isolation. His theory of population divergence and the origin of new species depended upon the evolution of traits that prevented individuals and populations from mating with each other.

Lythrum was known for its triple sexuality. There were three kinds of flowers. The female stigma could be tall, medium or short-styled. Each was accompanied by two sets of male stamens.  If the female was tall, the males were short or medium sized.

Darwin realized through his breeding experiments that greater the difference in height between these sexual organs, the greater the frequency of sterility. Mating between the unequal sized sexes in the same plant produced sterile seeds.  This was evolution preventing inbreeding and favoring cross pollination.

Adrian Desmond and James Moore in their biography, Darwin: The Life of a Tormented Evolutionist, write about Darwin's mischievous side:

" Talk about illegitimacy might have shocked the ladies guilds, at least coming from Erasmus Darwin's grandson. (Grandfather's own bastardizing experiments were still supplying tittle-tattle. At this moment Darwin suspected the widow of a botanical friend, Francis Boott, to be an illegitimate granddaughter of old Erasmus). But Darwin was stolid, methodical, reducing the love of the plants to cold, clinical calculation. Sterile seeds counts somehow fitted an unromantic, data-crunching age. Not for him Erasmus's flowery personifications, as styles and stamens bent to embrace in a kiss:

Two knights before thy fragrant altar bend,
Adored Mellissa! and two squires attend.

Still, he could tease. Solicited by a Mrs Becker for something edifying for her ladies' literary society, he posted 'On the Sexual Relations of the Three Forms of Lythrum salicaria'. Goodness knows how many red faces left after hearing that 'nature has ordained a most complex marriage-arrangement, namely a triple union between three hermaphrodites,- each hermaphrodite being in its female organ quite distinct from the other two hermaphrodites and partially distinct in its male organs, and each furnished with two sets of males' ".

There is no doubt that Darwin was an outstanding thinker. But he also was a hands on guy. His thinking was not vacuous or overly speculative.  He was a tinkerer and putterer.  He produced data. By cross breeding plants. By dissecting barnacles. By co-opting pigeon breeders and noting down the variation in the size and shapes of different breeds. Documenting tiny differences between individuals within groups was crucial to his case that complex structures could evolve by incremental changes over generations.

From life's little details he built the grandest theory of all.