Lithic literacy and the "forensic" methods of geoscienceJames R. Ebert, Earth and Atmospheric Sciences, State University of New York, College at Oneonta
My approach to teaching the methods of geoscience is founded on two related expressions of a single idea, which I use in nearly all the courses I teach. The first expression is in the form of a question that I often pose to my students: "What do we know and how do we know it?" It is the "how do we know it" part that encompasses the methods of geoscience. The second expression is borrowed from Murray (2004) – it is the notion that all geology is forensic geology. I do not mean the legal aspects of forensic, rather I mean the association that the word has with the reconstruction of events and processes from the physical evidence of those events and processes.
So, how do we know what we know and how can we reconstruct events for which there are no eyewitness accounts? The clues are "written in the rocks." However, before students can read the story they must develop what I call "lithic literacy." By this, I mean that it is first necessary to be able to recognize the clues before we can interpret them. In my classes, I stress the centrality of observation in the solution of geoscience problems. Bill Metzger, with whom I studied historical geology and stratigraphy as an undergraduate, often said, "Interpretations come and go, but a good description lasts forever." In developing lithic literacy, it is not only important that students make careful observations, but they must also come to realize that some observations are more useful than others are. For example, the texture of any rock provides clues to the processes that formed that rock. Observations of texture are generally more useful than observations of color, which may be influenced by weathering or the presence of trace elements.
Once students gain some facility with observation, I introduce interpretation by starting with modern analogs that are familiar to most students. Because I teach courses in Earth History and Sedimentary Geology, I use sedimentary structures. Most students have seen ripples and mud cracks in modern settings, so it is not a giant intuitive leap to interpret such structures when they occur in rock. Students quickly recognize that these structures are records of processes, unwitnessed, but which undoubtedly occurred. This is the geological version of "Who done it?"
From sedimentary structures, we reconstruct processes. Processes lead us to environments and from environments to paleogeography. This inductive approach differs somewhat from the other sciences in that we are working from multiple specific examples and deriving general principles. Other sciences tend to use a more deductive approach. On the other hand, once paleogeographic and stratigraphic frameworks are established we can make predictions to unexamined areas. Can we project how thickness, facies, etc. will change in these areas? These predictions are hypotheses, which are testable by observations in the unexamined areas. In this respect, the methods of geoscience do not depart radically from the methodologies employed by other sciences. However, geologic systems are inherently complex and commonly messy, unlike much of chemistry and physics, for example, in which controlled experiments, which manipulate one variable at a time, are the norm. Students commonly struggle with the uncertainty inherent understanding in complex, messy geologic systems. All scientific knowledge is tentative, of course, but students are not comfortable with the notion that their interpretations might be wrong. Further, they do not like the notion that there are other, possibly better explanations, which they have failed to envision. Part of my task is to help students develop some level of comfort with this uncertainty.
Murray, R. C., 2004, Evidence from the Earth, Mountain Press, Missoula, MT, 226p.