Friday, August 23, 2019
David Bercovici - Origin of Plate Tectonics - What a scientist sounds like.
One aspect of this blog is all about my own journey of discovery through knowledge acquired from the global community of scientists over the course of generations.
I do have strong opinions that are based on how I've processed the information I've accumulated so far. Within that frame of reference, it always seemed self-evidence that our moon's close proximity to Earth during the first billion years had to have a hand in starting plate tectonics on this planet.
I could not understand why geoscientists never discussed that aspect when writing about origins of plate tectonics. It simply didn't make sense to me.
But, recently listening to scientists such as David Bercovici, I've come to appreciate many aspects of that situation I had no clue of. Not that I've had any particular insights, but I have gained a world of appreciation for why the moon's tidal influence on the start of plate tectonic isn’t near as obvious as I was imagining.
It seems to me a great example of allowing facts to dictate my opinion. I appreciate I possess a fraction of the knowledge someone like Bercovici has accumulated - thus if his words reveal flaws in my own thinking - it's my duty to understand him, not simply to dismiss him.
As opposed to the agenda driven character, who is so self-certain that he allows his under-educated mind to conjure (and then believe) all sorts of fantastical under-informed rationalizations in order to dismiss the expert's knowledge.
See, truth doesn't matter to the self-certain - pushing agenda over substance is their priority.
Whereas in serious science honestly acquiring evidence that helps us gain better understanding IS the goal - while ultimate certainty is unattainable.
Be forewarned the following is a talk given to his peers, so it's a peek into how scientists speak with each other, rather than the crisp public talks I usually like sharing.
Professor David Bercovici Ph.D.
On the Origin of Plate Tectonics
2014 Fall Meeting
Session: The Birch Lecture topic Tectonophysics
Title: On the Origin of Plate Tectonics
Bercovici, David, Yale University, New Haven, CT, United States
The emergence of plate tectonics was Earth's defining moment. How and when plate tectonics started is shrouded in mystery because of the paucity of observations in theArchean as well the challenge of understanding how plates are generated. The damage theoryof lithospheric weakening by grain-reduction provides a physical framework for plate generation. This model builds on grain-scale processes to elucidate planetary-scale tectonics, and is consistent with lab and field observations of polycrystalline rocks and lithospheric shear zones. The grain-damage model accounts for the evolution of damage and healing (by grain growth) at various planetary conditions, hence predicts plate boundary formation and longevity, and how they depend on surface environment.
For example, the onset of prototectonics is predicted to require clement conditions to keep healing from erasing weak zones; conversely, cool conditions possibly required tectonics to draw down primordial CO2. Thus whether tectonics preceded a cool climate (and water) or vice versa is immaterial as they likely needed each other or neither would exist. Sparse evidence that prototectonics co-initiated with liquid water hints at the link between tectonics, water and surface conditions.
The establishment of wide-spread plate tectonics started between & 4Ga and 2.7Ga, and may have taken over a billion years to develop. Under Earth-like conditions, combining grain-damage with intermittent Archean proto subduction produces persistent weak zones that accumulate to yield well developed plates within 1Gyrs. In contrast, Venus' hotter surface conditions promotes healing and prohibits weak zone accumulation, which explains why plate tectonics failed to spread on our sister planet.
Damage and weak-zone inheritance may also influence plate evolution and reorganization in the modern era. Changes in plate direction, such as reflected in the Emperor-Hawaiian bend, leave weak zones misaligned with plate motion, causing oblique plate boundaries that persist for the age of the plate. Grain-damage within a cold subducting slab may also cause its very rapid detachment, and the abrupt loss of the slab-pull force could account for precipitous changes in plate motion, such as for the Pacific plate at both 47Ma and6Ma.
Cite as: Author(s) (2014), Title, Abstract T44B-01 presented at 2014 Fall Meeting, AGU, San Francisco, Calif., 15-19 Dec.
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For more on David Bercovici Ph.D. who was elected into the National Academy of Sciences in 2018: