IMPACTTECTONICS.ORG BLOG Rev. 2022-06-12

Gregory Charles Herman, PhD Flemington, New Jersey, USA

Punctuated Tectonic Equilibrium

Introduction

Stephen Jay Gould's and Nile Eldredge's remarkable theory of punctuated equilibrium; that biological evolution on Earth is marked by isolated episodes of rapid speciation between long periods of little or no change, is a more appropriate theoretical model with regard to Earthly tectonics than uniformitarianism, the current guiding principle of geology. In other words, plate tectonics on Earth results from the combined effects of short periods of bombardment and accretion from hypervelocity bolides (comets and asteroids) with subsequent, longer periods of stasis involving plate drift and reorganization.  Their theory was born from studying biological extinctions and speciation through geological time, with the former frequently used to partition historical geological time into the Eras, Epochs, and Stages constituting our international time scale (Fig. 1). When extended as such, their work help explain how Earth was assembled and evolves in a general sense.

Figure 1. Biological extinction rates as percentages over time based on observed and projected fauna populations and losses determined from Earth's fossil record. Graph adapted and modified from  https://courses.lumenlearning.com/wm-biology2/chapter/mass-extinctions/.  Sudden and dramatic losses of biodiversity called mass extinctions have occurred many times in Earth's history and often mark divisions of geological time. Biological revolutions often result from a combination of punches from bolide impacts immediately followed by the occurrence of large igneous provinces (LIPS) and tectonic revolutions. Many of the impacts charted above are oceanic and speculative in nature, are marked in blue, and await further testing. Those marked in purple are known. The sine curves superimposed on the chart before and after ~300 Ma are representative curves fit to cycle of biological extinctions as hypothesized by Rampino and Caldeira (2018).

And so here I sit on my 66th birthday at 7:00 am contemplating Earthly tectonics again. Only this time I'm starting a blog entry on the topic. Over 40 years ago I took a trip to Glacier National Park that inspired me to become a geologist in order to understand how mountains rise. That trip was not for pleasure, as I was a member of a unionized crew of industrial laborers working for an outfit from Granville, Ohio that had been contracted to recoat the cement casting pits for 20-foot-long aluminum ingots at the Columbia Falls, Montana Anaconda aluminum factory. Our crew traveled cross country that summer in a stake-bed truck towing a sand blaster, and on that west-bound trip we also saw the Northern Lights, Mount Rushmore, and Custer's battlefield. Prior to this, I didn't know about geology as I had never been introduced to it in my primary education in rural Ohio, or the smattering of college classes that I took at Ohio State branch campuses over the course of the next few years. I was 21 year old and just trying to figure out my next steps in life. I had just left the family hardware store working with my father and younger brother, and as I realized then, living like Richie Cunningham from the popular TV show Happy Days. But I wasn't happy doing that, and temporarily working as a union laborer gave me enough cash to head back to college for a degree, at least for a couple of semesters. During our stay on that trip, my boss introduced me to geology by repeatedly uttering, "This is a geologist dream". After finally inquiring, "What is a geologist?", he simply responded, "they study this."

The job required 24 hours on shift, followed by 48 hours off, when we got to recuperate and take time to explore the wilderness of the park. I remember fondly that pivotal moment of my life standing alone at the end of a rock promontory, overlooking a glacially scoured lake with the cold wind whipping upward against my face as I gently leaned into it, sturdied by my make-shift hiking stick. The white mountain goats were specks on the majestic cliffs formed by uplifted but relatively flat-lying strata. I recall pondering at that moment, what forces come to bear on a planetary surface that would make such mountains rise? I realized then what I wanted to study, and in due course, applied to Ohio University to enroll in their geology program. I was accepted, with most of my preceding 60 course hours of business administration and electives at branch colleges transferred so that I could enter the program during the following winter as a sophomore in my last trimester. I was a tad behind the declared majors that preceded me, so I ended up taking geomorphology at the same time as introductory geology. Geomorph was a 300-level course and I was soon overwhelmed with new information and concepts. Professor Geoff Smith however was succinct and thorough and I appreciated that.

Going to college at OU for geology was a crucial life decision from which I have benefited since in many ways. It was my foundation for a lifetime study of Earth science. I was introduced to structural geology there by Dr. Damian Nance, who influenced me to further direct my interests to focus on structural geology and plate tectonics that has since become my life's calling. In recalling my OU geology experience with respect to its influence on my scientific interests and endeavors, there were a few key moments then that sparked ideas eventually culminating is this entry.  The first was during a paleontology class when we were introduced to the concept of punctuated equilibrium by Dr. Royal Mapes. We used the Raup and Stanly textbook and I recall him professing the suitability of punctuated equilibrium when addressing aspects of biological evolution on Earth through time. It made a lot of sense to me then as opposed to strict phyletic gradualism that acceptance of Darwinian evolution naturally led to.

Another pivotal moment occurred during my senior year in a 400-level, Global Tectonics seminar taught by Damian and Dr. Thomas Worseley, an acclaimed stratigraphic oceanographer. At that time, Damian and Tom were formulating their 'pulsating Pangaea' hypothesis of repeated, supercontinent assembly and fragmentation following the principles of the newly proposed Wilson cycle.  Our class of about six upperclassmen had the privilege of participating in lively discussions and debate on the subject after delving into weekly reading assignments that fueled the desire. Their hypotheses were based on the work of Tuzo Wilson (1966) who first recognized and documented the probability of having reoccurring episodes of supercontinent assembly and fragmentation.

At that time and prior to the advent and use of global positions systems (GPS) along with modern, digital cartography, we were taught that Africa was relatively immobile on Earth's surface, and that supercontinent breakup and separation likely stemmed from thermal welting of a relatively immobile continental lithospheric that slowly rose above sea level, and with deep continental roots that provided a thermal blanket above upward-rising mantle plumes off Earth's core. Africa's relative non-mobility when compared with surrounding continents was deduced form the hot-spot reference frame that we relied upon before the deployment of satellites to measure actual plate motions. Earth's hot-spots are very Africa-centric because the largest mantle plume lies beneath Africa. But now we know that Africa is indeed moving too, in concert with the other lithospheric plates, and there is a myriad of motivating mechanisms that propel Earth's exterior plates around its surface.  And so, my scientific viewpoints on tectonics have evolved in a lifetime, and echo the principles of punctuated equilibrium, insofar as local stresses cause subsequent adaptations that tend to quickly proliferate and then fester over time until the next revolution. Considering that both biological and tectonic revolutions are spurred by the same mechanisms, periodic bolide bombardment and accretion with mountain building and subsequent development of large igneous provinces, this approach provides a framework from within which we can achieve a more comprehensive and thorough understanding of Earth's history and evolution.

Realization 

After having studied and practiced structural geology and tectonics throughout most of my life, I have come to realize that plate-tectonic theory has a critical flaw from the general geological communities' reluctance to include grounded stresses from catastrophic, large-bolide impacts as motivating agents of tectonic cycles. Uniformitarianism, the modern, guiding principle of geology may account for processes operating 99% of the time, but it's the 1% catastrophic forces that perturb the existing equilibrium and forces new biological, tectonic revolutions to occur rapidly thereafter, until stasis is achieved, or a new equilibrium is reached. Others have noted this flaw in applying exclusive gradualism and uniformity, and in particular I draw you attention to the work of Ursula Marvin, a Harvard-Smithsonian NASA geologist that also recognizes the need to elevate global catastrophism into a more comprehensive plate-tectonic theory. Following is a quote from Dr. Marvin's essay published in 1990 on Impact and its revolutionary implications for geology from Geological Society of America Special Paper 247, Global Catastrophes in Earth History:

   "Impact-generated craters, eruptions, wildfires, and extinctions, whether they are sporadic or periodic, have no place
    in the serene uniformitarian world of Hutton and Lyell, or the world that has been envisioned by the geological
    community for the past two centuries. Rather than to invert the definition of a venerable word, it is time to recognize
    that bolide impacts is a geological process of major importance, which by its very nature, demolishes uniformitarianism
    itself as the basic principle of geology."

You are spot on Ursula. I argue that punctuated equilibrium is a more applicable principle for tectonics that more appropriately accounts for Earth's destructive perturbations and subsequent blooms.

LIP Triggers and Crustal Tsunamis

The repeated pairing of large-bolide impacts and igneous LIPS in time indicates the probability that hypervelocity impacts suddenly rupture the lithosphere and trigger the release of igneous melts, especially where the lithosphere is suddenly extended in the wake of oblique impacts like that seen for the Syria-Sinai Planums impact-strewn field on Mars with respect to Olympus Mons and Tharsis Montes. Decompression melting of partially-melted mantle material outside of the 660 kilometers shock envelope occurs along large extensional faults formed in extensional blast sectors arising from an oblique impact, which most impacts are in nature.

As I recently pointed in the 2020 blog Beyond the Craters, recorded human history only reflects time when plate tectonics has operated at the gradual rates that we characterize using uniformitarian principles. Relatively constant, horizontal plate motions on the order of millimeters to centimeters per year are the standard course stemming from recent, empirical observations. But catastrophic, instantaneous propagation of seismic waves radiating outward away from a large-impact sites are difficult to fathom because they can hypothetically raise mountains suddenly when terra firma gets rung like a bell and its carpet gets rumpled and welted. We have not experienced this as modern humans and our established viewpoints reflect our geological viewpoints gained over a mere two centuries. If we theoretically recognize the potential of impact tectonics to suddenly impart widespread tectonic revolutions as part of plate-tectonic theory we then become aligned with Gould and Eldredge's (1977) punctuated equilibrium as a more inclusive guiding principle of plate-tectonic theory, one that directly reflects our discretization of time. As Gould (1987) wisely stated “if we equate uniformity with the truth and relegate the empirical claims of catastrophism to the hush-hush unthinkable of theology, then we enshrine one narrow version of geological process as true a priori, and we lose the possibility of weighing reasonable alternatives.”  One such alternative tectonic viewpoint is that of Buthman (2022) that repeatedly illustrates the natural resource potential of large, multi-ringed impact basins on Earth and the relative importance of such structures as part of the tectonic process.

And now, here we humans are as an animal species on Earth, sometimes ruminating on the causes and effects of mountain and basin-forming events during a time of tectonic status. I can only imagine what the experience must be like to watch a large asteroid enter the atmosphere and impact the planetary surface with such ferocity that the crust is instantly compounded, faulted, and warped into new structures. In all likelihood, it would be a brief human experience for the only way to survive such events would be to have safe haven in an underground or subaqueous facility at some remote distance from ground zero because of the severe, ensuing atmospheric and ground disruption. But imagine if you will the propagation of the seismic body and surface waves generated by the impact as they dissipate and spread about, aligned with circumferential basins and mountains. These events have helped build mountainous structures and large basins around us in a geological instant. They raise welts on the planetary surface with amplitudes now mapped as the highest and deepest land positions on Earth. And yet, we continue to ignore these effects in plate-tectonic theory. Perhaps because we're afraid of the implications from feeling hapless in prevention. For whatever reason, it's a shame, because until we do integrate the effects of catastrophic and perhaps periodic bombardment of Earth by large asteroids and comets into their rightful place in our tectonic legacy, we are truly missing the mark. 

References

Bond, D.P.G. and Grasby, S. E., 2020, Late Ordovician mass extinction caused by volcanism, warming, and anoxia, not cooling and glaciation: Geology v. 48 , no. 8, p. 777–781. doi: https://doi.org/10.1130/G47377.1

Buthman, D. B., 2022, Impact crater tectonics; The future of resource exploration: Published in the United States, 285 p. ISBN: 979-8-9853971-0-0

Eldredge, N. and Gould, S. J., 1972, Punctuated equilibria: an alternative to phyletic gradualism", in "Models in paleobiology": Schopf, T.J.M., ed., Freeman, Cooper & Co, San Francisco, pp. 82-115

Racki, G., Rakociński, M., Marynowski, L., and Wignall, P.B., 2018, Mercury enrichments and the Frasnian-Famennian biotic crisis: A volcanic trigger proved?: Geology v. 46, no. 6, p. 543–546, doi: https://doi.org/10.1130/G40233.1

Rampino, M.R., and K. Caldeira, 2018: Comparison of the ages of large-body impacts, flood-basalt eruptions, ocean-anoxic events and extinctions over the last 260 million years: A statistical study. Int. J. Earth Sci., 107, no. 2, 601-608, doi:10.1007/s00531-017-1513-6.

Wilson, J. Tuzo (1966). "Did the Atlantic Close and then Re-Open?": Nature, v. 211, p. 676–681. doi:10.1038/211676a0. ISSN 0028-08

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