Book Review: The Story of Earth
If you pick up Robert M. Hazen’s The Story of Earth expecting the planet’s inhabitants to be the stars of the show, a quick check of the table of contents should be sufficient to disabuse you of that notion. There, the word life’s first appearance is associated with Chapter 6, which begins 127 pages into the work. Which is not to say that life is not discussed before then, but it is to say that life, of utmost significance to us, was of very little significance to the planet until the primitive prokaryotes that spun up likely a bit before the Earth’s 1 billionth birthday became so commonplace as to alter the planet’s atmospheric chemistry by virtue of their existence, adding enough oxygen to the atmosphere to turn the Earth’s surface red with rust and inadvertently engineering an environment that fostered the continued existence, reproduction and diversification of those early organisms into the myriad of forms that have appeared on—and, despite several potentially apocalyptic disruptions, managed to cling to—the terrestrial stage during the last 3.5 billion years. Despite eons of unconscious terraforming by life as a whole and centuries of obliviously intentional extraction and reshaping by us, the geological processes that shape everything from continents and oceans to sand and soil have carried on as physics and chemistry dictate, and it is those processes and the planet they have produced that are the leads in Hazen’s telling of the story.
I have read enough geology-focused books to know the bones of the plot from the Hadean to the Holocene more or less by heart. In most of these works, the first 3.75 billion or so years play prologue to the five acts of their drama: yes, yes, there was the Big Bang and a dust cloud around the sun and a big ole thwack from another planet that produced the moon and some Milankovitch cycles and Snowball Earth and Hothouse Earth, but now let’s get this party started with the Cambrian explosion or the great Ordovician biodiversification event or the Cretaceous lives and times of critters in the Western Interior Sea or the dinosaurs and their demise or the rise of us plucky little mammals. Other authors’ prologues, however, are the sole substance of Hazen’s first four acts; the Cambrian and everything after are the Act V denouement.
Despite covering 3.75 billion years in 231 pages, Hazen’s pace is somewhat leisurely. The Earth evolves chapter by chapter, with each chapter’s title conjuring the face of our world during the years measured in its pages. (Whether via authorial intent or coincidence, those same chapter titles conjure Kim Stanley Robinson’s Mars trilogy as well.) I knew about the collision between Earth and Theia that resulted in our Earth-moon system, but the relation between that event and the tortured formation of the planet’s first basalt crust in its aftermath came clear in my mind with the Chapter 3 title “Black Earth.” Well, yes, I guess the planet would have been pretty black for a while with all those volcanoes chugging out gobs of basalt, interrupted only by cracks and cones of red-hot lava. Those same volcanoes and the chemistry that accompanied them resulted in the ocean-covered blue earth of Chapter 4 and, another 100-150 million years down the line, in the production of the granite crust that formed the cratons discussed in “Gray Earth” in Chapter 5.
My favorite chapter of the book covers the so-called “boring” billion—i.e., the billion years from 1.85 billion years ago to 850 million years ago. Just as historians of the medieval period have made the case that the “Dark Ages” were far from dark, Hazen provides evidence that the evolution of both life and the planet were chugging along at a steady, if unremarkable, pace. The plates beneath the proto-continental cratons that had crunched together to form the Columbia supercontinent pulled apart then, 200 million or so years later, began to move toward one another again to form Rodinia. Near the start of the boring billion, around 1.7 billion years ago, there was an explosion of mineral diversity. The beryllium, boron and mercury families expanded from a handful of species to dozens in the cases of beryllium and mercury, hundreds in the case of boron. The reasons for this flowering are not yet understood, but Hazen and fellow geologists like Linda Kah and Ed Grew are working to track them down—and are thereby revising the science of mineralogy by considering the roles of both “geological time and geographical place” (200) as well as chemistry and biology in mineral formation. Hazen was one of eight authors who published “Mineral Evolution” in 2008, a paper “posit[ing] that Earth’s mineralogy has evolved through a sequence of stages, each of which saw changes in the diversity and distribution of minerals. Hence the narrative arc of this book [i.e., The Story of Earth}, in which planets progress from mineralogical simplicity to complexity, from only about a dozen minerals in the dust and gas that made our Solar System to more than forth-five hundred known mineral species on Earth today—two-thirds of which could not exist in a nonliving world” (201). I find it astounding that this perspective is so young and thrilling that there is still so much to learn by examining our world through this paradigm.
The work’s final chapter, “The Future,” offers prognostications of the planet’s fate in reverse chronological order, starting with its near-certain demise in the maw of the dying sun. The “good news” is that there won’t be much, if any, life around to deal with that catastrophe. Some two billion years from now, the sun will, before swallowing our planet like Joey Chestnut gobbles a hot dog, grow both brighter and hotter, evaporating the oceans and leaving the Earth’s surface “barren and baked” (260). Cheers. For the billions of years between now and then, however, the planet’s existence should be more or less business as usual. 250 million years from now, the continents will come together again in a new supercontinent named either Novopangaea or Amasia (the name depends on how the plates move and the new supercontinent is configured). Sadly, we may not be here to name it—considering, as Hazen does, the potential disasters of asteroid impact, megavolcanoes and ice ages and the present disaster of global warming—but regardless of whether our species survives, the Earth will keep chugging along as dictated by the laws of physics, chemistry and biology. There is some solace in this fact, but I selfishly wish the beauty of the life that currently surrounds me, from the curve of a swallow’s wing in flight to the current of humanity that flows through Shakespeare and Woolf, would endure forever. We are the blink of an eye. We have barely begun.