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.