Saturday, March 21, 2015


I am by training both a paleontologist and a geologist. Although I’ve published papers on fossil vertebrates, the most important work I’ve done over the past decade have probably been my studies on stratigraphy (the ordering of sedimentary rock layers and the fossils they contain), which tells us most of what we know about the order of events that occurred in the past (in fact, up until the mid 20th century it told us pretty much everything we know; radioisotopic dating, which put actual numbers on rocks in millions of years was not developed until the 1950s, and is still much more rarely applied). Stratigraphy allows us to determine the order of environmental and biotic events in Earth history, and therefore potentially to understand the reasons for them. I can say, without (I think) too much presumption, that my particular field of research is not only a cornerstone of paleontology but a vastly under-appreciated one; mistakes made in determining the ordering of rock layers can lead to important misunderstandings about when and why environmental and ecological changes occurred in the past.

Martin Rudwick’s The Great Devonian Controversy is one of the most extraordinary books on geology or paleontology I’ve ever read. It is also a book that has a more personal meaning to me than for most readers, even for most geologists, as it deals with the blossoming of stratigraphy in the early 18th century as a tool for reconstructing the history of life. The tale centers on the debate, primarily between British geologists Roderick Murchison and Henry de la Beche, on the stratigraphic relationships of sedimentary rocks in the Devonshire region of southwestern England. What began as an apparently minor local geologic problem in one corner of Great Britain eventually expanded to encompass the entire world, and to shape our understanding of the early history of complex life on Earth.

Roderick Murchison (left) and Henry de la Beche.
They had their differences.

In 1834, de la Beche relying largely on facies (sedimentary rocks with a certain set of characteristics, usually relating in some way to the environment in which they formed), interpreted the Devonshire strata, including a distinctive coal-producing horizon, as representing a strata far older than the great Carboniferous coal seams of England. These conclusions were based partially on his interpretations of the complex structural folding in the region (which turned out to be badly in error), but also on the apparent lack of an unconformity in the region between the coal-bearing strata and the lower rocks in the sequence.  These lower rocks seemed to resemble the “greywacke” rocks of the newly recognized Cambrian and Silurian systems just being described by Murchison and Adam Sedgwick. De la Beche therefore concluded that the coal beds must be only a little younger, and therefore much older than the Carboniferous.

However, Murchison and Sedgwick argued that the plant fossils of the Devonshire coal beds were too similar to those of the Carboniferous coal seams to be that much older. They based this opinion on the newly developed discipline of biostratigraphy, which claimed that fossils of the same type could be used to identify rocks of the same age. As a consequence, they argued that there must be a major unconformity separating these coal-bearing beds in Devonshire from the lower “greywacke” rocks, even though de la Beche pointed out that this unconformity could not actually be found in the region.

De la Beche was also an accomplished illustrator. If you've seen just one old timey picture
of prehistoric life it was probably this one, which shows the Jurassic marine life of England.

Over a roughly eight year period between 1834 and 1842, this apparently minor and provincial stratigraphic puzzle came to involve not only de la Beche, Sedgwick, and Murchison, but a handful of other British geologists with varying levels of prestige, including William Smith's nephew, John Phillips.  Some major names in early geology, including Charles Lyell, George Grenough, William Buckland, also chimed in at various points in the debate; Lyell supporting Murchison, Grenough supporting de la Beche. Sedgwick played the role of diplomat between the egotistical and ferocious Murchison (who didn't like to be disagreed with and was fighting to build a lasting geologic legacy), and the defensive de la Beche (who was trying to secure government employment and was therefore extremely defensive about his reputation).

At stake was not only the competence of the geologists involved (particularly de la Beche) for interpreting strata, but the relative reliability of different methods for determining the relative ages of rocks that were just being developed for the first time. Was biostratigraphy a reliable method, or could fossils of the same type be found in rocks of vastly different age? Could sedimentary rocks of the same type that formed in similar environments (“facies”) be assumed to be the same age everywhere? Can fossils of the same type be found in different facies? These issues still factor into modern stratigraphy and our reconstruction of Earth history. Just as importantly, this local stratigraphic problem resulted in Murchison incorporating the observations and data collected by various British and continental geologists to almost single-handedly construct the basic framework of the Paleozoic timescale in less than a decade.

This enormous relevance of this episode in the history of geology would make the Great Devonian Controversy an important book, but what elevates it to a true masterpiece is the exhaustiveness of Rudwick’s documentation and analysis. It’s been said that more is known about how Charles Darwin developed his ideas on evolution and natural selection than for any other scientific theory in history. Much the same can be said of the Devonian debate, and for the same reason: The 19th century naturalists involved not only made exhaustive notes documenting changes in their thinking, but wrote enormous letters to each other with great regularity. This documentation has been carefully preserved, and Rudwick makes full use of it. 

The level of detail to which Rudwick can trace the activity and changing attitudes of the players, sometimes literally on a day by day basis, is nothing short of extraordinary. Perhaps even more amazing, at least to me, is how much the discussions, arguments, and practical problems of these pioneering geologists working almost 200 years ago echo my own experiences working with modern geologists and paleontologists. The arguments between Sedgwick and Murchison on the relative importance of superposition and biostratigraphy, dealing with conflicting schedules in organizing joint fieldwork, and trying to prepare presenations for meetings are all remarkably familiar.  My own favorite example is Sedgwick putting his collaborator off on completing a paper Murchison needed to present their recent findings at a meeting, and Murchison’s admonishment to Sedgewick that he should stop making excuses about being to busy and having the flu and just finish the goddamned manuscript.

It also certainly helps that Rudwick is an exceptionally good writer, presenting this flood of information in a way that is both comprehensive and completely clear. In spite of the deluge of place names and characters involved, there is never any doubt about exactly what the various players are thinking and arguing, or how their interpretations of the geologic evidence shift with new information and ideas.

Rudwick’s analysis also considers the nature of changes in scientific thinking. Dismissing the simplistic and sometimes na├»ve models for scientific change advocated by philosophers such as Popper and Kuhn, Rudwick is able to document beyond any question the much more complex process by which ideas develop in science. The final analysis of the book presents a view of science that is considerably more comforting than that sometimes advocated by cynics who claim that scientific thinking is ruled by contemporary social, political, and personal issues. Instead, Rudwick’s analysis of the Devonian controversy shows that the (probable) truth of nature can eventually be revealed in spite of these handicaps. Most of the major players in the Devonian controversy, including the egotistical Murchison, eventually converged on a single model for Devonshire that fit all of the available evidence and could be confirmed by examining rocks across Europe. The journey to this compromise model is far too fascinating for me to spoil it (although the title of the book kind of gives it away). 

In spite of the high personal and professional stakes these geologic rivals placed on being right, nearly all eventually accepted this compromise position for two simple fit the evidence and it held up to repeated testing, the ideal reasons for scientific hypotheses to succeed. Instead of stubbornly denying the evidence, as cliches of the egotistical scientist would predict, Murchison in particular just pretended it had been their idea all along (a lot of the correspondence and discussions at meetings documented in the book involve various workers, especially de la Beche and Murchison, bitching about not being given enough credit for their ideas). 

Again, the similarities between how these early workers behaved and my own experience with modern geologists and paleontologists can be downright painful.

For those wanting a story with lots of drama about how social inequality and dueling egos shape scientific activity, there is certainly plenty to be found in The Great Devonian Controversy. However, at its heart the book is about something far more interesting: smart people trying to solve a problem. After years of controversy and the burning of much shoe leather, Murchison and Sedgewick were finally able to achieve the Holy Grail of science: a model that explained all the observations, and had predictive power. Ultimately, the book is about one of the great triumphs of historical science.