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J. Zalasiewicz 2010. The Planet in a Pebble. A Journey into Earth's Deep History. xvi + 234pp. Oxford University Press. Price £16.99, US$27.95 (HB). ISBN 978 0 19956 970 0.

Published online by Cambridge University Press:  22 February 2011

Euan Clarkson*
Affiliation:
Edinburgh
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Abstract

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Copyright © Cambridge University Press 2011

Jan Zalaziewicz tells the story of an ordinary pebble of grey Silurian slate picked up from a beach in Wales, its components and history, going back as far as the Big Bang 13.7 million years ago. This is a wonderful book, in which hard science is explained in simple but effective terms. The prose is exquisite, and the starscapes and Earthscapes are conjured up with magical inward vision. Open a page at random, and read, as I have just done ‘Field geology is the ultimate forensic science, the art of the possible, where one combines as much evidence as one can get hold of, with as much ingenuity as one can muster – and also with a keen sense of the limitations of one's deductions’. Who would not envy the ability to write like this? But purple prose is absent in this enchanting volume. This is all good stuff.

The first chapter takes us to the Big Bang and the formation of the elements now present in our pebble. Vast star systems originated, collisions of stellar bodies and young planets took place on an unimaginable scale. Our planet eventually stabilised, with convection currents below an evolving lithosphere (Ch. 2); quartz crystallised from granitic magma, to become an almost ubiquitous component of sedimentary rocks. Amongst the quartz fragments in a sediment we find rare minerals, including zircons (Ch. 3) that are often zoned, thereby recording events in their history as they grew.

So, the grains of our pebble, with their separate histories, came together in an oxygen-starved deep sea, off the Avalonian continent. On this deep sea floor mud accumulated, affected from time to time by turbidity currents and sea level changes, chiefly the result of glaciations (Chs 4 & 5), all neatly explained. Conditions were ideal for preserving the planktonic graptolites which rained down after death, to be preserved, unscavenged (Ch. 6). Their nature, biological relationships and stratigraphical uses are treated lovingly, as is their preservation, with fine drawings and colour plates. Although other planktonic animals, apart from chitinozoans and acritarchs, are lacking, they may leave chemical traces (Ch. 7), including carbon isotopes. We learn that radioactive rhenium, decaying to osmium, has real potential for reliable radiometric dating; a prospect previously unknown to this reviewer.

Chapters 8–10 bring us ever closer to the present time. We read of the marine half graben on the edge of Avalonia in which our pebble formed, its burial deep in the sedimentary pile, and what happened to it during its long time of ‘imprisonment’. ‘Prison, in this case, was a place of reform’, we are told, because of chemical changes in the mud, soon to become rock. The remaining chapters discuss tectonic events, the rise of the Welsh mountains, folding, faulting and conversion of the mud into slate. As the overlying mountains were eroded, and our ‘pebble’ nears the surface, pressures lessen and it eventually comes into the zone of rich bacterial life, which likewise leaves its mark. Ice, penetrating the upper layers of rock, alternately melts and thaws it, fracturing the rock. Our pebble, finally isolated, falls into the sea to be worn and polished by the tides. Eventually it is picked up by one of those recently arrived humans, to be taken to the laboratory, and studied by a range of optical, electronic, and expensive chemical equipment, which reveal its history, as so perfectly narrated here.

To portray the long history of the components of this pebble is an original and bold undertaking; the scope is phenomenal. We read about all kinds of things ranging from stellar theory, through mass-spectrometry and rare element analysis, to the geological history and ancient life of Wales to erosive processes operating now. I have found this to be a wonderful read, from which I have learned much that is new, written in elegant, expressive, but eminently readable prose. Professional, amateur geologists, teachers, students, and the informed general public would all derive very much from reading this book.