SCALES #56: grand under-sweep
Hello!
A lot of thinking about geologic time recently. (And no, not just as I look back at the length of my Ph.D., amiright?? *embarrassed rimshot*) Recently I finished reading Timefulness by Marcia Bjornerud, subtitled “How Thinking Like a Geologist Can Help Save the World”. (Hip to it via BLDGBLOG.) In the best way, it’s very much a work by a liberal arts professor. (Lawrence!) At the outset Bjornerud describes what got her hooked on geology as an undergraduate:
“[Geology] creatively appropriate[s] ideas from physics and chemistry for the investigation of unruly volcanoes and oceans and ice sheets. It applied scholarly habits one associates with the study of literature and the arts—the practice of close reading, sensitivity to allusion and analogy, capacity for spatial visualization—to the examination of rocks. […] To think geologically is to hold in the mind’s eye not only what is visible at the surface but also present in the subsurface, what has been and will be.”
That perspective, seeing the continuities between different disciplines of thinking, immediately sold me on the book. (Also sold on: being unapologetically anchored to the distinctive geologic landscapes underlying Wisconsin and the Upper Midwest; mentioning paleotidal evidence for how days on Earth have lengthened over time, à la SCALES #6.)
Bjornerud focuses throughout on conveying what it means to think geologically, how geological knowledge is constructed. Several of the chapters chronicle how geologists gradually developed an increasingly detailed understanding of the Earth’s age and history. Bjornerud takes a sweeping view but provides enough texture about specific scientific questions and breakthroughs to keep me engaged, like how the first geologic clock was the Victorian-era fossil record, later followed by the rise of geochronology due to understanding radioactive isotopes and the increasing power of mass spectrometry. With this scope, Bjornerud is able to trace recurring patterns in geology over the history of the discipline. Powerful organizing ideas, such as uniformitarianism, reappear in new contexts but also sometimes reveal their limits and break down. Arguments from different approaches, such as astrophysics or genetics, appear to contradict the geologic record until certain assumptions are corrected.
Bjornerud is sensitive to the important role played by many styles of geology, ranging from painstaking detailed quantitative measurements to broader conceptual leaps of intuition. In one passage, she shows how none other than John Ruskin had a truer insight than a prominent geologist of his day into how the Alps formed:
“There is an appearance of action and united movement in these crested masses, nearly resembling that of sea waves… fantastic yet harmonious curves, governed by some grand under-sweep like that of a tide running through the whole body of the mountain chain.”
Bjornerud also argues we need to have a better feeling for the time scales of the Earth. Only with such a view can we understand the contingency of the Earth’s current climate. Human societies have largely built up over a relatively stable period, climatologically speaking, but the Earth has also experienced periods of extreme instability. Bjornerud also points out we don’t think about the vastly different time scales over which human activities will have an impact. We really don’t have a feeling for what kind of actions have a ten year time horizon, or a thousand years, or much longer.
It was enlightening to me to see how at the longest time scales of the Earth, there’s not a true equilibrium. Time’s arrow does move forward as the mantle slowly cools, the sun brighten and expands. There have been a series of different atmospheres, one after another. There have also always been endless feedbacks between different parts of the Earth system, in particular between the sorts of grinding geological processes I think of as unaffected by anything else and the biosphere. Reading about this gives me a different perspective when I see the latest ideas about possible warming feedbacks. It feels a lot less hypothetical, having a slightly better feeling for all the kinds of strange jumps and feedbacks that happened in the past.
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Which is all to say, Timefulness helped me to understand better some of the background to two talks I went to last week. One was by Tapio Schneider, a climate modeller at Caltech, looking at how stratocumulus cloud formation can break down under high enough carbon dioxide levels. Having a feeling for where the Paleocene–Eocene Thermal Maximum falls in the Earth’s timeline. The value of the paleoclimate as a testing ground for climate models. Thinking about what was different and what was the same about tens of millions years ago compared to hundreds of millions of years ago compared to billions of years ago.
A second talk was by paleoclimatologist Lonnie Thompson of ~The~ OSU. I’m generally prettttty suspicious of heroic narratives of science, but really, I don’t know how else to view collecting ice cores from tropical glaciers before they’re lost forever. Hauling equipment to the tops of mountains and then racing the ice core samples to refrigeration, sometimes with packs of yaks carrying insulated coolers. Thompson had some striking side-by-side charts where he showed how the isotopic spike from mid-20th century nuclear tests were simply missing from some recent cores. I remember him saying something along the lines of, “you can see time is melting off the top”—glaciers as a fragile, disappearing accumulation of time. A glacier he traveled to on New Guinea is projected to vanish in the next few years. He’s racing to collect a new core from the very top of the highest-altitude glacier in the Andes while it still holds as complete a record of the past as possible.
Alongside that, Thompson conveyed the human-scale calamities associated with losing these glaciers. The diminishment of freshwater supplies that entire societies rely upon. Catastrophic local changes to the terrain near the glaciers where people are trying to eke out a livelihood. Geologically sudden changes are happening, and though the Earth’s time will inexorably continue, human societies are ill-prepared to adapt.
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And finally, it all makes me appreciate anew how research studying the detailed chemistry of the contemporary atmosphere, like I work on, is the thinnest slice of contingency sitting atop eons of processes that happened to lead to this particular atmosphere, with these aerosol particles, these physical processes, these chemical pathways. (Defending Thursday!)
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Of course it warmed my heart to see an appendix listing different time ~scales~ of Earth processes.
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—Adam