Darwin's House Plants, Water Diviners, Geology Podcast

 A couple of good articles and a geology podcast.

1) “Spontaneous Revolutions” Darwin’s Diagrams of Plant Movement: Darwin's unbounded curiosity for nature led him down many unexpected research pathways. Towards the end of his long career, his restless mind noticed the growth patterns of his house plants. Determined to understand more about their motion and the stimuli, he spent hours tracking tendrils grow and came up with innovative ways to record their movements on paper. Natalie Lawrence has written a lovely essay on this lesser known chapter of Darwin's life and work. 

2) Trust, cost go greater depths to sustain unscientific water divining practice: Large swaths of Indian agriculture is desperately dependent on access to groundwater. Simrin Sirur explores the reliance on water diviners in south India. Diviners use sticks, coppers tongs, coconuts, magnetic compass, and chains with keys as their instruments for sensing groundwater. Despite all this unscientific baggage, many diviners are not all that ignorant. They have a knowledge of the local landscape and groundwater availability. Their prediction relies more on their past experience and a dollop of common sense. 

I must tell you about my experience with a diviner. My neighbor requested that I accompany her to a plot of land outside Pune. She had hired a diviner to help her locate groundwater. We picked him up en route. He was the late Pandit Bhimsen Joshi's son! On reaching my friend's property he got to work with copper tongs. After a few minutes of walking  up and down the site the copper tongs started shaking. He indicated the spot to drill and suggested going down to a depth of 150 feet. On the way back he cheerfully told us that he knew that the adjacent plot owner had struck water at 150 feet. Past experience and common sense go a long way! 

3) Geology Bites Podcast:  Conversations with Geologists: Oliver Strimpel has had quite an unusual career beginning with a doctoral degree in astrophysics. He later became the director of the Computer Museum in Boston and then a patent attorney. But geology beckoned him. He has worked alongside geology researchers trying to date rocks and unravel the timing of movement of the Karkoram fault in Ladakh. Geology Bites grew out of his passion for the subject. You will find a wide range of geology topics discussed on this site. 

I have so far listened to experts talk about radioactive waste disposal, continental crust composition, the inherent bias in the global sedimentary record, and on the evolution of minerals through geologic time. All have been excellent. The talks are about half hour, so they don't tax your patience too much. 

If you have free time coming up this Diwali, I recommend you dive into this collection of geology talks.

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.