Breakthroughs in Geology
Geology, like all sciences, is continually developing and ideas behind it evolve over time, through the hard work and expertise of many people. Having said that, a number of ideas have dramatically revolutionized the science, such as uniformitarianism in the 18th century and, more recently, the theory of plate tectonics.
In his new book, Breakthroughs in Geology, Graham Park, Emeritus Professor of Tectonic Geology at the University of Keele, UK, describes the ideas that he believes have transformed earth science, devoting a chapter to each of his chosen concepts, moving through time to the most recent developments. As Prof. Park says in his preface, such a list is bound to be subjective and others may choose differently, but he discusses all his breakthroughs in a manner that allows you to appreciate the importance of interlinking ideas and disciplines. He goes into each in some depth, while describing them clearly in a manner that the non-specialist will understand, all amply illustrated. He briefly summarizes each new concept, and links it to previous interpretations on the topic, before indicating its impact on geological science. He also discusses the influential players involved in each breakthrough, with brief bios and descriptions of their seminal papers.
The book is a fascinating read and makes you admire the intellectual imagination and integrity required to make that first step toward a breakthrough; it takes bravery and self belief to move against accepted norms, as some of the early geologists did. James Hutton’s description of the Earth as having “…no vestige of a beginning – no prospect of an end…” was at odds with the contemporary view of an unchanging Earth created in its present form over a time span outlined in the Bible. The first two chapters are devoted to those early scientists, such as Hutton, Lyell and Darwin, who used a range of disciplines to identify the main principles of the newly emerging science of geology.
The third chapter looks at the concept of continental drift, which developed as geologists wrestled with the question of how mountains formed once ideas such as ‘the contracting earth’ were abandoned. Although Wegener is rightly considered to have formulated and promoted the idea, the author explains the way in which his work built on that of many other geologists. Wegener’s theory took time to be accepted, until a mechanism behind the drift of the continents could be found, ultimately leading to the idea of mantle convection (Chapter 4). Proving this concept illustrates how interlinked scientific disciplines are needed to develop these breakthroughs; for instance, the discovery of radioactivity by physicists enabled geoscientists to date rocks and gain insights into the make-up of the interior of the earth, further elucidated by the new science of geophysics.
Chapter 5 discusses important developments in structural geology, allowing highly strained rocks to be described and understood for the first time. This led to the investigation of shear zones and the realization of their significance with regard to major crustal displacements.
Most Influential Breakthrough
The following chapter concentrates on plate tectonics, which resolves the main issues surrounding a mechanism for continental drift and is, in Park’s opinion, “the most influential breakthrough in earth sciences since Darwin.” The concepts of seafloor spreading, mid-ocean ridges and subduction at oceanic tranches eventually developed through extensive seafloor mapping coupled with the use of paleomagnetic dating and some ‘out of the box’ thinking. This section also covers new concepts like transform faults and the growing understanding of the significance of volcanoes and earthquake zones. The author points out the large number of earth scientists involved in fleshing out the theory of plate tectonics, none of whom can take full credit but all of whom provided significant input. Several of the subsequent chapters discuss topics that have proved important in refining and deepening the plate tectonics theory, such as ophiolites (Chapter 6), back arc basins and trench roll back (Chapter 9) plus hot spots and mantle plumes (Chapter 10); all equally fascinating. In Chapter 8, Park discusses fault system kinematics, a concept that has hugely changed and influenced the way structural geologists think about faults and faulting.
The final two chapters cover relatively new concepts, one of which, sequence stratigraphy, has played a significant role in hydrocarbon exploration. In a remarkable leap from accepted thinking, Peter Vail and his team at Exxon in the 1970s looked at the boundaries between rock layers, instead of the rocks themselves, in order to correlate distinct chronostratigraphic units on a continental or even worldwide scale. While there are limitations to the concept – it is of little use with many carbonates, for example – sequence stratigraphy combined with seismic imaging revolutionized the work of exploration geologists. The final chapter discusses gravity spreading, and the role extensional forces generated by gravity play in tectonics, touching on salt tectonics and the more recent ideas around channel flow.
Prof. Park rounds off his book with an excellent glossary explaining terms encountered in the book, as well as a comprehensive chapter-by-chapter reference list. Initially, I was surprised by the absence of a final concluding chapter, but I think he made the right decision. Each chapter has a summary and conclusions in the form of a short Postscript outlining the significance of, and subsequent developments in the breakthrough featured, so there is no need for repetition of these points at the end. As Prof. Park points out in several places in this excellent book, geology is constantly evolving and there will be many more breakthroughs in the future. Meanwhile, the research, the generation of new ideas, and the ensuing debates all continue!