I was once asked during a job interview, “Is geology a science or an art?”
I am still wondering what the correct answer is to something that sounds like a trick question, but what I do know is that both scientists and artists require inspiration. This can come in all manner of forms, but we can definitely be inspired by those who have paved the way for our ongoing endeavors. For our profession, that means being inspired by the great geologists.
The history of geoscience is marked by the work of exemplary scientists who changed the way we think about the Earth, its history, processes and resources. Some made huge intuitive leaps, recognizing, for example, the immensity of geological time or the mobility of the continents. Others described rocks, minerals and fossils in the field or laboratory and provided vital data that allowed theories to develop. Still others embraced new technologies and paradigms, such as geophysics, that enabled what cannot be observed directly to be inferred. Many led colorful lives or overcame adverse circumstances. These seem like people worth knowing about, not least, for the inspiration they provide.
Thinking About the Earth
The history of geological thinking is a long one, with scholars in both ancient Greece and Rome contemplating the history of the Earth and how that related to the rocks beneath their feet. In the 5th century B.C., Xanthus of Lydia saw shell shapes in rocks located far from the coast and concluded that these regions must have once been submerged beneath the sea. Leonardo da Vinci drew similar conclusions centuries later.
Nonetheless, it was not until the mid-17th century during the late Renaissance and the arrival of the Danish scientist Nicolas Steno in Florence that modern geological thinking can be said to have begun. Steno’s observations, during his brief dalliance with geology, were seemingly simple by modern standards. He observed, first, that in a normal succession of rocks, the oldest are at the bottom and the youngest at the top. Second, he noted that sedimentary rocks are laid down horizontally. Third, if they are not horizontal, then they have been folded or faulted by geological processes. Finally, fossils are the preserved remains of ancient creatures. Simple observations, yet, these notions suggested that the rock record and its fossil content represented a chronology – effectively a book of Earth history – waiting to be read.
It was not until more than 100 years later that the book of Earth history began to be read in earnest. During the Age of Enlightenment, the Scottish intellectual James Hutton argued that, from a consideration of the processes of rock creation and their subsequent deformation, the age of the Earth had to be, by human standards, immense (“the abyss of time,” as described by Hutton’s friend and fellow intellectual, John Playfair). How immense was uncertain, but certainly much older than might be determined from a straightforward and literal interpretation of the Bible or other religious texts.
Geology is Born
Geology as a stand-alone subject was born in the late 18th century with the work of Hutton and others. Hutton was not the “Father of Geology” as he is sometimes portrayed, but he was an important catalyst in developing inductive thinking about the age of the Earth and geological processes. Others, such as Abraham Gottlob Werner, Georges Louis Leclerc, Comte de Buffon and Peter Pallas were contemplating similar issues in Germany, France and Russia, respectively. Around the time of Hutton, “geology” as a term with its current meaning was introduced by the Geneva-based naturalist Jean-André Deluc in 1778, although it had been used with a broader meaning (including the study of plants and animals) since the 15th century (as the Latin word “geologia”).
Werner and Hutton were on opposite sides of the controversy that existed between Neptunists and Plutonists, which occupied geological, and indeed popular, thinking in the late 18th century. Werner had promoted the notion that all rocks, including granites and basalts, were either deposited or precipitated out of water (Neptunism), while Hutton favored the view that granites and basalts were the products of heat within the Earth creating molten magma (Plutonism). His observation of cross-cutting intrusions demonstrated this. By the beginning of the 19th century, Neptunism as an explanation for crystalline rocks, such as granite, was effectively no longer in vogue. Instead, rock classifications concentrated on the concepts we now know as igneous, metamorphic and sedimentary.
The next major step in the history of geology was to determine that the fossil content of sedimentary rocks could be used as a key to understanding that a given rock unit could be associated with a specific period of Earth history. This allowed correlation to other rocks deposited during the same period: the science of stratigraphy was born. Recognition of distinct strata permitted the mapping of these layers as they occurred at the Earth’s surface and, equally importantly, enabled a prediction to be made of what might lie below the surface. William Smith in England and Georges Cuvier in France pioneered this thinking at the end of the 18th century into the beginning of the 19th century.
The Debate of the Century
Geological research focused on two distinct activities for the first half of the 19th century. There were those concerned with the description and classification of rocks, minerals and fossils and, most notably, the subdivision of Earth history. British geologists such as Sir Roderick Murchison and Adam Sedgewick were at the forefront of this campaign, with European counterparts such as Alcide d’Orbigny not far behind.
Other researchers were concerned with the geological processes operating on and within the Earth, and how these processes may have operated in the geological past. In other words, how rocks came to be formed and subsequently deformed. Foremost amongst these was Sir Charles Lyell, who considered himself to be on a crusade to make geology scientific. Observations led to theories about how geological processes operated. In Lyell’s view, these processes were gradualistic — a steady state Earth in which geological processes were the same in the past (uniformitarianism, following on from ideas earlier expressed by Hutton).
By contrast, many geologists in continental Europe favored the theory promoted by Georges Cuvier that the Earth had experienced a more eventful past, with catastrophes punctuating Earth history, these events being associated with tectonics, extinctions and major changes in deposition (catastrophism). The debate of the importance of uniformitarianism versus catastrophism continued throughout much of the 19th century and persists in some circles even today; although most geologists are now happy to accept that Earth history is a response to a combination of both gradual and sudden processes.
However, many 19th-century geologists, as today, were both describers/classifiers and interpreters, attempting to add color to the pages of Earth history by envisaging past worlds. What did a Jurassic Earth look like and what creatures inhabited it? Which geological processes were operating to leave us with the rock record we see today? Such intriguing questions are equally valid nowadays and engage the imagination of most geologists to a greater or lesser extent, even if their focus is often on the fine detail. The romance of imagining our past Earth is something that still draws students to study geology and requires both an understanding of geological classification and of geological processes.
By the second half of the 19th century, much of the basic classification work had been completed (although this continues to the present day in order to provide ever-increasing precision), and greater numbers of geological scholars were focused on interpreting the rocks they studied in terms of the processes responsible for their creation and deformation. Such studies ranged from the small-scale – for example, Henry Sorby and his interpretation of rocks in thin-sections by use of a microscope, to the large scale – such as Eduard Suess and his interpretation of the formation of mountain belts. Geological disciplines were becoming increasingly integrated. Although Western Europe continued to be a hub for geological research, American researchers, such as James Dana, Louis Agassiz and T.C. Chamberlin, were now also making important contributions.
Geologists, however, were still faced with the perplexing conundrum – how old was the Earth? It was widely accepted to be millions of years old, but exactly how many remained an unknown. The discovery of radioactivity, as the 19th century passed into the 20th century, provided the breakthrough. Radioactive decay of elements present in certain rocks could be measured and interpreted in terms of absolute age. At last, there was a clock of Earth history!
The undisputed pioneer of this research was the great British geologist Arthur Holmes. Thanks to Holmes and those who followed him, geologists could use an understanding of the age of the Earth and the duration of the chapters in Earth history to help elucidate the processes responsible for forming and deforming rocks and explain modes of evolution represented by the fossil record.
Knowledge of true geological time allowed thinking on a grand scale. Alfred Wegener was able to envisage continents drifting on the Earth’s surface throughout geological time while others, such as T.C. Chamberlin and Amadeus Grabau, began to recognize a rhythm to the Earth’s sedimentary record. These notions, in turn, spurred the paradigms of plate tectonics and sequence stratigraphy in the second half of the 20th century.
Even though geologists are often asked who “discovered” plate tectonics, the answer is that no single person can be said to have done so. Papers by Dan McKenzie and Bob Parker or by Jason Morgan can be cited as the first to describe plate motions as translations and rotations on a sphere, but these built upon a long series of discoveries by many other researchers who worked on the bathymetry of the deep ocean (such as Mary Tharp), the nature of oceanic and continental crust, sea-floor spreading, transform faults and convection within the interior of the Earth. Plate tectonics is arguably the most recent great geological discovery – the culmination and integration of understanding geological time and geological processes. Of course, new geological discoveries are made every day, but nothing (as yet!) can compare to the scale of the plate tectonics paradigm.
In the same way that people use the term “Peak Oil” to describe the time of peak oil supply to the market, the term “Peak Geoscience” has recently been heard. Briefly: has our development of geological science reached its zenith? Therefore, have we entered into a time of synthesis, the gathering of detail and of consolidation?
Personally, I doubt this. Geological research still has many questions to answer and the application of data science is likely to reveal startling new insights.
Geology is becoming increasingly holistic and integrated with other sciences. Earth systems science integrates a variety of processes operating at the full range of timescales (from hours to millions of years) and spatial contexts (from local depositional processes to global tectonics), thereby providing insight into sediment supply from mountain source to sediment sink within a depositional basin. Paleoclimate research, such as that carried out by Maureen Raymo, works in a similar manner, providing insights for modeling of future climate trends. Alongside such holistic approaches, it is likely that advances in technology and data science will transform geology by teasing out patterns in geological data that are beyond the capacity for easy recognition by humans.
For the readers of the EXPLORER, it goes without saying that innovation and petroleum geology go hand in hand. Petroleum geologists have been both innovators (for example, Peter Vail) and the avid adopters of innovation. Every advance made by great geologists contributes to our ability to more accurately predict the geology of the subsurface and its resource potential. For example, plate tectonic models have allowed us to reconstruct the palinspastic position of sedimentary basins, allowing us to better determine tectono-stratigraphic history and the evolution of petroleum systems within any given basin.
Geological research continues across all branches of the subject and is expanding from the confines of the Earth to consider the geology of neighboring planets and their moons. No doubt there will be more great geologists to emerge and be recognised over the coming years.
The geologists working before the 20th century went out into the field and made observations that then led to theories of geological processes. During the 20th century, technological breakthroughs made a huge difference to geological thinking. For example, the advent of radiometric dating, the recognition of paleomagnetism, and the use of geophysical techniques and remote sensing are immense. That does not belie the importance of field work – there is no substitute for gathering data – but rather than armed simply with a hammer, hand-lens, compass-clinometer and paper notebook, the field geologist now has a wider variety and more sophisticated set of tools at his or her disposal, including drones and 3-D imaging technology. Geoscience is far from being at its peak!
In order to encourage others to learn more about the great geologists, I, with support from Halliburton, have produced a book which reviews the lives and scientific contributions of 35 of the more significant contributors to our subject. It is freely available as an e-book at joom.ag/ggLa and printed copies are available on request while stocks last (contact me at ).