MODELING GEOLOGY

Models are ubiquitous in geology, but the word can include an astonishing variety of meanings and devices. All are useful in varying degrees to represent earth and solar system processes and structures both large and small that cannot be observed directly. As has the rest of the science, the uses of models have changed over time. I will make a brief historical survey of the types of models and give some indication of their usefulness.

Models can respresent either the physical entities and structures or the processes of geology. They may be static representations of structures such as folds, or have the ability to be put in motion. They can be mental constructs. Mathematics may or may not be involved. A model such as the orrery included all of the above, with the use of mathematics to understand the solar system and construct it. It is also a physical model based on a mental construct of the way the parts of the solar system move. Crystal forms (observable) were modeled early, followed by suppositions about the integrant molecules (unobservable) that resulted in their shape.

Models may be categorized as: mental, or theoretical, conceptual, or historical; physical, as in devices or constructions; chemical; experimental; mathematical or statistical; graphic, as in maps, sections, relief reconstructions or block diagrams; or computer or computer-aided models. Many fit into more than one category. Use of the computer has enabled far larger amounts of data to be accounted for.

As in all sciences, one could argue that models are necessary in geology despite their limitations. There is no doubt that geology has gained from their use. Folding, crystal structure, sedimentary processes, crustal formation and motion, all have been clarified, if not solved, by the use of models.