Title

The Principle of Actualism as the Structuring Principle for Reconstructing the Geologic Past of the Earth

Abstract Course

Earth sciences are both functionalist (they study the manner in which the Earth functions) and historical sciences (they reconstruct the past of the Earth). Many scientists (Gould, 1989, for example) highlight the trend towards regarding these sciences as "soft" or "merely descriptive" as opposed to "hard" and "rigorously experimental" science because they require the tools of history for explaining various natural phenomena (the Cretaceous extinction, the origin of life on Earth, etc.). Geologists cannot however build the history of the Earth in a strictly determinist framework or as a cosmogonic system (Hooykaas, 1963). This is not possible for three main reasons:

- Only modern and superficial geological processes or events are directly observable. Moreover, they are very complex.

- If geologists want to construct an “actual” past which is the opposite of purely imagined reconstitutions, they need empirical clues and traces of the Earth’s past.

- The reconstruction of the past of the Earth must take into account the contingency that leads us to consider that other options might exist. As Gould (1989, p.278) wrote: “Historical events do not, of course, violate any general principles of matter and motion, but their occurrence lies in a realm of contingent detail”.

In order to avoid only considering the idea of a possible past, and to stay within the limits of a “real” past (an “actual” past), and in order to stabilize certain sections of the past, scientists must mobilize the principle of actualism and empirical traces of the Earth’s past. The methodological principle of actualism (uniformitarianism) represents a safeguard against overly speculative and ad hoc reconstitutions. This assumption states that the present is the key to the past and, more specifically, that the phenomena at the origin of past geological changes (their geological causes) existed and still exist in the nature as it functions today (Gohau, 2003; Oldroyd, 2003). So this principle is “the bridge that enables our imagination to go from the present to the past, to visualize with some confidence what no human eye has seen” (Hooykaas, 1963, pp. XI-XII). Geologists have built thus a reasoned history of the Earth by articulating the present with the past and by mobilizing empirical traces of the past. How have geologists dealt with the problems of historical geology? What controls do they exert over their reconstruction of the Earth’s phenomena or events (Orange Ravachol, 2013)?

In this paper, based on epistemological references (Lyell, 1833; Whewell, 1847), we will show how the principle of actualism has become of great importance as the structuring principle of the historical reconstitution of the past of the Earth and we will compare how, on the one hand researchers and on the other hand secondary school students dealwith the problems of historical geology.

References

• Gohau, G. (2003). Naissance de la géologie historique. Paris : Vuibert-ADAPT.
• Gould, S. J. (1989). Wonderful life, The Burgess Shale and the Nature of History. New York : W.W. Norton & Company, Inc.
• Hooykaas, R. (1963). The Principle of Uniformity in Geology, Biology and Theology. The Nederlands: Leiden.   
• Lyell, C. (1833). Principles of geology. London: John Murray.
• Oldroyd, D. (2003). The Earth Sciences. In David Cahan, ed. (2003) From Natural Philosophy to the Sciences. Chicago: University of Chicago Press.
• Orange Ravachol, D. (2012). Didactique des sciences de la vie et de la Terre, entre phénomène et événement. Rennes: PUR.
• Whewell, W. (1847). Philosophy of the inductive sciences. London: John W. Parker, West Strand.

Contact

denise.orange@univ-lille3.fr