The Planet in a Pebble: A journey into Earth's deep history [Hardcover]

You pick up a rock and it's just a rock. Jan Zalasiewicz picks up a rock and sees a history of the whole Earth. That's because Zalasiewicz is a geologist, so rocks have more meaning to him than they do to most of us. He has imparted some of his specialized meaning in _The Planet in a Pebble: A Journey Into Earth's Deep History_ (Oxford University Press), one of the most accessible works of geology for the layman available. William Blake rhapsodized on the possibility that one could "see a world in a grain of sand," but of course he was speaking of the mystical and poetical. He probably would not have gotten much inspiration from Zalasiewicz's scientific view, but there is inspiration aplenty here for those who want to look at demonstrations of human cleverness. It is quite wonderful that we can make sense of how the Earth came to be and can understand how certain rocks came to have the characteristics they do, since it requires tracing back billions of years. Zalasiewicz does the tracing back, indeed, to the Big Bang and the eventual formation of the Earth right up until the pebble he describes is brought out to be picked up on the beach. The scope of the story is thrilling, and if you can't picture every step he describes in every chapter (few of us can imagine adequately, for instance, time extending back for such periods), there will always be more astonishments in the next one.

"A pebble of gray slate from a Welsh beach - perhaps from somewhere like Aberystwyth, or Clarach, or Borth on the west Wales coast." Why pick such a source? Simply because Zalasiewicz has had a "career devoted to untangling the intricacies of Welsh slate," a rock he says is underappreciated and "has often had, alas, the reputation of being wet, grey, and monotonous." So the choice of pebble might be arbitrary, but we can take for granted that any pebble from anywhere else has someone taking the same tenacious geological stare at it. "In some ways," writes Zalasiewicz, "the pebble is like one of the newer computer chips, tightly packed with more information than one could ever surmise from gazing on its smooth surface." First things being first, the book starts with the Big Bang, long before there were all the elements that the pebble is made of. There is plenty of violence, but there are other periods in which the pebble (or the rock mass wherein it was formed) just waits, shifted in millions of years from one locale to another and infiltrated with ions carried by water into it. It's a geological story, but there is plenty here to learn about cosmology, astronomy, and chemistry. Biology is surprisingly important, for the pebble contains fossils of graptolites, animals that date the rock with fine precision. Neodymium isotopes tell when the stuff that makes up the pebble was released from the Earth's mantle, for instance. There are zircon grains, and the decay of radioactive potassium, and many more up until 1945 when all rocks above ground began to be tinged with the leavings of the nuclear age. There is even lichenometry, whereby the exceedingly slow and steady growth of lichen gives a clue about how long the rock on which it is growing has had a surface for its growth. The different chronometers have been calibrated and matched because geologists have to deal with such huge spans of time and "have racked their brains to find as many ways as possible to say _what_ happened _when_. As racking goes, it has been quite fruitful, all told." Toward the end of the book, the pebble, inching toward the surface, begins to feel the effects of climate (not seasonal weather, but the broader temperature patterns). It had, before this, drawn any heat it felt from the Earth's interior. Eventually the external climate would make an impression on it, but it would have been millions of years after that before it felt any seasonal change, and even longer for it to have come to the surface. Once it got there, though, things could change a lot. Split off from its mother rock and washed by tides, it might have lost as much as half its mass in one storm season as it banged around on its neighbors.

Zalasiewicz winds up in a final chapter with a few pages about the pebble's future, where in a few billion years it will perhaps join all the molecules on Earth as they are swept into the Sun. Maybe bits of it will be exploded out into cosmic dust that become part of a new solar system with new planets. The speculation on the pebble's fate is similar to the mind-stretching understanding of what it has already been through. It is an astonishing journey, and Zalasiewicz has provided a valuable and detailed account of it, beginning to end.

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"It is an ordinary pebble. It's one of millions that washes backwards and forwards on the shoreline or piles up on riverbanks or lines your garden path. Yet that pebble, like its myriad kin, is a capsule of stories. There are countless stories packed within that pebble, more tightly than sardines in the most ergonomic tins." --Jan Zalasiewicz

I was reminded of Carl Sagan's saying, "We are star stuff," and the pebble is most qualified to be included in 'We'. Where life was essentially nonexistent, yet the pebble does preserve signs of life. Even though the pebble itself is an eroded version, out of its parent magma, in a Welsh cliff side. The same chemical compounds contained within it trace the origins of our planet Earth, our solar system, the milky way galaxy and the universe. Although the records contained within the pebble are often incomplete, they still allow us to feel the pulses caused by the planetary change, "In some ways the pebble is like one of the new computer chips, tightly packed with more information than one could ever surmise from gazing on its smooth surface," Zalasiewicz apologetically explains.

"The Planet in a Pebble" is what the title conveys: an attempt to extract the Earth's story from a small rock, in this case a smoothed, blue-gray pebble, streaked with white, found along the Welsh coast where the author has spent much of his career. A competent geologists knows that even the smallest rock carries within innumerable threads of inscriptions revealing the history of planet Earth. Like the strings of tiny fossils embedded in the rock, core competence in physics, chemistry, and biology instruct history run through "The Planet in a Pebble." Zalasiewicz's troubadour talents, while keeping the pebble in sight, he skillfully guides readers through material that might have left them out in delusion.

This engaging book is a celebrity reckoning on geology, in the widest sense. It begins with the origin of elements and ends with the demise of the Solar System. Traveling backwards in time to explain how it came into existence, the book picks the pebble as his muse. In the book's early chapters, almost any pebble would have been served, yet, the authors careful selection of pebble expands the second half of the book in a certain direction. So, the mineral particles in the pebble were eroded off the long-lost continent of Avalonia a long time ago, and, more recently tiny crystals of pyrite (iron sulfide) settled on the ancient mud to fill in the body cavities of tiny animals. Now, despite the pebble static nature, it did not remain in one place. Baked by the heat of the earth, the parent rock layer underwent metamorphosis that took of millions of years, moved along and shoved into what is now the Welsh coast.

As one might expect from an author who has written, provokingly, about the meaning of time in formal stratigraphy, the importance of chronology is creatively illustrated. I found the book to be most successful in the parts that combined the aspects of geology that were less familiar to me, given I studied Mineralogy and Petrology in one course, Geo 101. In effect, he is giving free reign to the urge that many scientists have to let the imagination off the leash without having to go into detail about the supporting data and arguments. In this ways, the numerous possible ages of the pebble are skillfully uncovered, each encoded in a different part of its constituents. No reader of this book will ever kick a pebble down the road or even pocket one from the beach in a careless way ever again.

Excellent text, but the kindle edition does not reproduce the color plates. I would not buy the kindle edition until it has the plates

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