The Surprising Story of Life on Earth

The inexorable movement of Earth’s tectonic plates, repeatedly creating massive continents and then tearing them apart, is an underlying plotline to the story of life on this planet.  Since the first appearance of life, a mere 100 million years after the birth of the planet 4.6 billion years ago, the influence of continental creation and destruction on the environment and, thus, on the fortunes of life has been profound.

In his relatively recent book, paleontologist Henry Gee, a senior editor at Nature, tells that part of the story well, but goes much further, painting with broad brush strokes a narrative of how life has evolved and survived, amid repeated extinction events.  The narrative he penned is informed and insightful, marked by humor and a steady stream of surprises.  This is a book that moves easily and quickly through the billions of years it covers.  Not for nothing did Gee title it:  A (Very) Short History of Life on Earth:  4.6 Billion Years in 12 Pithy Chapters (published in 2021).

Early on, he writes, “Perhaps the most amazing thing about life – apart from its very existence – is how quickly it began.”  (p. 5)  It strikes me that an ineluctable drive to exist undergirds life’s almost immediate appearance on the new planet, and that this also helps to explain why the history of life is the history of responses to change.  It’s a call and response pattern whereby life survives repeated episodes of devastation, episodes that Gee often ties to the creation of massive continents (e.g., creation of Pangea completed during the Permian) and to the breakup of those massive continents (e.g., breakup of Pangea beginning at the tail end of Triassic), all having profound effects on climate and habitable areas.

Evolution is part and parcel of this ebb and flow pattern.  Gee’s account offers up many examples of evolutionary change sparking still more change, all in the service of survival.  His narrative of the Cambrian is one of predator and prey engaged in a dance whereby new methods of attack spark new methods of defense which in turn . . . .   For instance, in the Cambrian, descendants of Saccorhytus (a very early enigmatic animal) chose not to build armor, but, instead, to evolve a means of escape though a “swishing tail.”  (p. 31)  This notochord would evolve into the spinal cord.  With the evolution of a spine came a cascade of changes, allowing animals to become more complex and bigger.  “All vertebrates are visible to the naked eye.”  (p. 36)  Of course, evolution doesn’t let a useful invention go to waste, and many vertebrates did evolve armor.

As I mentioned, Gee’s account is full of surprises.  One of the most startling, to me, was that of the import of the anus.  Who knew that the evolution of the anus in the Precambrian would have such far reaching effects?  He describes how plankton had simply let wastes flow everywhere out of their bodies, feeding oxygen-consumers in the water column.  But, once a discrete anus emerged “in some species of otherwise undistinguished worms,” the result was “a revolution in the biosphere.”  (p. 18)  In his telling, poop in concentrated packets was expelled from the anus and settled to the ocean floor, drawing the oxygen-consumers to the bottom, with the result that “the seas, once turbid and stagnant, became clearer and still richer in oxygen – enough to enable the evolution of larger life forms.”  (p. 18)

But, wait, that’s not all.  The anus in time lead to orientation to animals with a mouth at one end and an anus at the other, it became “a distinct direction of travel.”  And this led, eventually, to an arms race as animals began eating one another.  Yes, there is a leap there, but Gee is such a gifted writer that the reader, well, this reader, is happy to make that jump with him.

His is a very rich account of life on Earth, and it’s also idiosyncratic, each of its 12 chapters is centered on one or a few developments that, in Gee’s eye, are central to the broad portion of life’s history under review.  For instance, chapter 7, titled “Dinosaurs in Flight,” principally about the Jurassic and Cretaceous, is a wonderful exposition of the avian nature of dinosaurs. 

Flight, according to Gee, was in the works for dinosaurs from their beginning.

Dinosaurs and their immediate relatives spent millions of years accumulating everything needed for flight:  feathers, a fast-running metabolism, efficient air cooling to keep it under control, a lightweight frame, and a singular devotion to egg laying.  (p. 99)

Clearly, not all dinosaurs flew or kept flying once they did fly.  Flying is demanding of an animal’s physiological resources.  Notes Gee, it’s “an expensive habit . . . . so, it is not surprising that many flyers gave it up when the opportunity arose."  (p. 105)

Or consider that his chapter on mammals (succeeded by chapters that consider primates and then hominins).  Gee has embraced the view of mammals that I’ve expressed in this blog before (in the post titled Mammals All The Way Down, November 29, 2021) – they weren’t just biding their time in shadow of the dinosaurs, they were actively evolving.  Gee begins this chapter by discussing the evolutionary changes that equipped mammals with a hearing ability more sensitive than anything that had existed previously in vertebrates.  The physiological changes required to achieve this new level of hearing are, in Gee’s skilled telling, a product of complex evolutionary change repurposing bones.  Though mammals during the reign of the dinosaurs may have been away from center stage and, certainly, not the main act, they were evolving with gusto.  He stresses, “They were a venturesome bunch and not to be kept down.”  (p. 121)

After several chapters tracing the evolution of primates into hominins into humans, Gee ends with a final chapter (The Past of the Future) that leaves no doubt that ours is just a brief moment in the history of life on this planet and that we humans are fated to suffer the eventual fate of all life on the planet – extinction.  He writes:

Within the next few thousand years, Homo sapiens will have vanished. The cause will be, in part, the repayment of an extinction debt, long overdue. The patch of habitat occupied by humanity is nothing less than the entire Earth, and human beings have been making it progressively less habitable.  (p. 188)

He speculates on how the planet will change in the future and how life will be affected.  I was particularly taken by the humorous footnote he inserted covering the whole of this sobering exposition:

I should say that from this point onward, most of what I say is conjecture, or what scientist call making stuff up.  As someone once said, prediction is very hard, especially about the future.  (p. 268, footnote 17, note number appears on p. 189)

Bottomline, Gee posits that humanity won’t survive and all evidence of our existence, relative to the billions of years life existed on Earth will be negligible.  But, despite that lack of enduring legacy, or, actually, because of it, Gee counsels us that it’s important “to preserve what we have, to make our mayfly existence as comfortable as possible, for ourselves and our fellow species."  (p. 207)

This is an engaging, witty, and informative read.  I do have one quibble:  I think plants get short shrift in Gee’s telling of the story of life.  They’re not ignored, but the drama in his account has mostly to do with the trials, tribulations, successes and failures of animals.

Living Things: A Review of Turning to Stone

 When I began this blog many years ago, my father questioned its title:  Fossils and Other Living Things.

"I don't get it.  Fossils aren't alive," he objected.

I replied that I found that fossils have stories to tell and experiences to share if we are open to communicating with them.  They aren't silent.  I don't think I went much further because his puzzled expression was not encouraging.  At least he'd expressed some interest, even if it was mostly couched in doubt.

I could have gone on and on.  I might have described the multi-hued Miocene shark tooth that lets us know that it came into contact with particular kinds of minerals in its journey to becoming a fossil (e.g., my post titled Colors - Fossils and a Graphic Story About Darwin).  I could have suggested that I love that all fossils carry a living backstory if we choose to explore its taxonomy or its evolutionary history or the people involved in describing that story.  It's an infatuation to which many of the posts in this blog attest, beginning as early as my sixth one titled What's In A Name? Part Un).  Perhaps he would have enjoyed learning that fossils can lie about their history (e.g., the Elvis taxa which I discussed in the post titled Witticisms in the Face of Mass Extinction).  In the end, I don't know that any of this would have made much of an impression.  One needs, I think, to appreciate this understanding of fossils by coming to it with a willingness to challenge the literal, supported by an openness to the poetry and complexity of natural things.

So it is no wonder that I found structural geologist Marcia Bjornerud's new book Turning to Stone:  Discovering the Subtle Wisdom of Rocks (2024) compelling.  (I do not provide page numbers with the text quoted below given that I read an ebook version.)

It's a marvelous memoir in which she recounts her many different roles:  student, scientist, woman in a male dominated field, academic, wife, mother, and widow.  In the process, she highlights the evolution and growth of the geological sciences over the past several decades, and the maturation of our understanding of the geological processes that make, and have made, the planet.

She tells her story in ten chapters, each highlighting a rock that had significant importance at a different stage of her life:  from the 500 million-year-old sandstone deposited on an ancient oceanside beach that generated the sandy soil marking her childhood in Wisconsin; to the mysterious 700 million-year-old diamictite, a clastic sedimentary rock, she studied in Svalbard as a graduate student; to the 450 million-year-old sedimentary (and, in her telling, boring) dolomite, deposited on an ancient continental shelf, that undergirds the landscape around the Ohio campus where she earned tenure; to the 1.7 billion-year-old granite produced in the cauldron of an ancient continental volcanic arc and now quarried near the Wisconsin university where she thought she'd found a measure of harmony in her life only to experience a period of turmoil.

Given her field of study within the science (structural geology), the stories these rocks have to tell invariably involve some aspect of the upheaval of seismic and volcanic action, the building up and tearing down of mountains, and the movement of tectonic plates and continents.  (On second thought, those are elements in some part of the history of every rock on Earth.)  There's quite a lot of violence in this account, but, as she counsels, much good comes of it.

There are several recurrent themes in this tale, none more important than Bjornerud's relationship with, and attitude toward, rocks.  In the prologue titled Ice, set in Svalbard, a Norwegian archipelago in the Arctic Ocean, she leaves no doubt about a specific perspective that animates the book.  Early in her academic training, she is a graduate student in Norway exploring evidence of tectonic action.  The landscape speaks to her in a way that harkens back to her childhood in Wisconsin when she felt at one with a responsive natural world.

In the sciences, one of the deadliest sins is animism - describing inert entities likes glaciers and mountains as if they were living beings.  And yet, in Svalbard it was undeniable that the austere landscape was alive, its rocks and water, ice and air in constant conversation.  The terrain was animate, sentient, and creative.  It would just take me thirty years to say that out loud.

She states that out loud often in the course of this memoir.  "This book is an invitation into my geocentric worldview in which rocks are raconteurs, companions, mentors, oracles, and sources of existential reassurance."  In her telling, rocks communicate, remember, reveal, wait, are cryptic, are incommunicative or inarticulate, sometimes mumble, . . . .

Embedded in the book are engrossing lessons in geology.  What comes through most clearly to me is how unique Earth is of all the planets.  Bjornerud's treatment of the tectonic forces at work on the planet Earth stands out.  She notes that, of all the planets, ours is the only one that has moving plates.  This continuous movement of plates, in particular the subduction of one plate under another, provides a constant source of communication between the interior of the planet and the exterior, a communication that is critical not only to the structure of the planet as we know it, but to the presence of life here.  The rocks that undergird her story are intimately involved in this repeated construction and destruction of stone.  "The Earth makes no distinction between creation and destruction."

Other themes run throughout the memoir, particularly, that, in the pursuit of short-sighted monetary gain, we have subjected the natural world to wanton destruction and exploited native peoples in that pursuit.  We erroneously believe we are in charge, that we have control.  The rocks know better.  Further, she inveighs against the notion that the Earth we know today was preordained, fated to be what it is.  Reflecting on the history of life from the microbial to the multicellular complex, she notes,

None of these things - though now literally set in stone - were then preordained; given the happenstances of planetary and biological evolution, Earth's story could have unfolded quite differently.

Here, as elsewhere in the book, she does not shy away from drawing life lessons from the rocks, to wit, "My path into geology felt anything but predestined."  Perhaps most prominently in this vein is the notion that the Earth's sustaining processes of creating and destroying, with the dangers and rewards of the cataclysms involved, are mirrored to some extent in the arc of change in her life where roles and relationships change, sometimes abruptly. 

Perhaps change is the key to this book.  The Earth is vibrant, living, and changing.  Rocks undergo change, sometimes slowly, sometimes violently.  Our understanding of the rocks has changed and deepened over her lifetime.  At one point, while in an academic building's basement, she contemplates an array of neglected crates containing rocks collected years ago.  The rocks have not changed in those relatively few years, whatever their histories before being collected.  She muses,

The rocks have remained as they always were, while our interpretations of them have vacillated and evolved.  The same is true for the events of our lives; the past is immutable, but its meaning changes with time.

This memoir merits and rewards our attention.