Terra Incognita: Explanation and Reduction in Earth Science

Abstract

The present paper presents a philosophical analysis of earth science, a discipline that has received relatively little attention from philosophers of science. We focus on the question of whether earth science can be reduced to allegedly more fundamental sciences, such as chemistry or physics. In order to answer this question, we investigate the aims and methods of earth science, the laws and theories used by earth scientists, and the nature of earth‐scientific explanation. Our analysis leads to the tentative conclusion that there are emergent phenomena in earth science but that these may be reducible to physics. However, earth science does not have irreducible laws, and the theories of earth science are typically hypotheses about unobservable (past) events or generalised—but not universally valid—descriptions of contingent processes. Unlike more fundamental sciences, earth science is characterised by explanatory pluralism: earth scientists employ various forms of narrative explanations in combination with causal explanations. The main reason is that earth‐scientific explanations are typically hampered by local underdetermination by the data to such an extent that complete causal explanations are impossible in practice, if not in principle.

Acknowledgements

A paper on the philosophy of earth science cannot be written without discussions with many earth scientists, most of them in the Faculty of Geosciences at Utrecht University. They cannot be mentioned all. The discussions in the research group ‘Knowledge, Normativity and Practice’ of the Faculty of Philosophy, Vrije Universiteit Amsterdam, as well as discussions with Victor Baker, Gerbrand Komen and Arno Wouters at the first Dutch Philosophy of Geosciences Symposium (Utrecht, 2005) are gratefully acknowledged. Suggestions by James McAllister and two anonymous reviewers were very helpful in improving an earlier version of this paper.

Notes

[1] We use the term ‘causal explanation’ generically, for the type of explanation employed in the physical sciences (in contradistinction to narrative, functional, and teleological explanation, for example). Of course, we are aware that this type of explanation can be further specified in a variety of ways, but for present purposes this may be ignored (cf. Section 4).

[2] ‘Geology’ is meant by Laudan to include many disciplines like mineralogy, sedimentology, structural geology, geomorphology, geophysics, oceanography, paleontology, etc.

[3] However, notwithstanding its great importance, the theory remains largely irrelevant for many earth scientists. For example, hydrologists studying local groundwater flow in deltaic deposits, and geomorphologists studying small‐scale sediment transport processes on hill slopes, rivers, and coastal seas, will probably never refer to the theory of plate tectonics. For a climatologist, biogeographer, and oceanographer, the current layout of continents may be important as specifications in boundary conditions, but their interests do not extend to the explanation of these boundary conditions. Thus, although plate tectonics is important in earth science, it does not play the role of unifying theory comparable to natural selection in biology.

[4] Note that it is ‘a large range of scales’ and not ‘all scales’. The self‐similarity breaks down at both ends of the scales. The high end is the extent of the phenomena, which cannot be larger than the atmosphere in the case of clouds, or a continent in the case of rivers. The low end is the size of sand grains or molecules or atoms; the self‐similarity cannot become smaller than this size. This need not be a problem, though. As Koperski (2001) argues, all representations (like laws) in science have this property. For example, fluid flow is governed by the (physical) Navier–Stokes equations. But this is continuum mechanics in which molecules or atoms, for which interactions would be described in discrete particle mechanics, have no place: “continuum models like those in fluid mechanics ignore the small‐scale facts” (Koperski 2001, 697, emphasis in original). So, in self‐similarity, we may also ignore the small‐scale facts and the large‐scale breakdown.

[5] According to Tucker (1998, 65), unique events are topics of why‐questions that radically underdetermine all potential explanations. He argues that there are no acceptable scientific theories that can explain unique events because such events occur once and only once. Yet, according to Tucker, we may question whether all alleged unique events are really unique. He therefore makes a distinction between absolutely unique events and relatively unique events. Relatively unique events are events that only seem really unique relative to a given context of scientific development and theoretical perspective. As science progresses towards more advanced levels of knowledge, the event may be discovered to be non‐unique after all. For example, consider comets. These celestial events were once regarded as truly unique and individual, but Newton and Halley showed that many comets are recurrent and share the same physical properties. The mass‐extinction of 65 Ma ago was caused by the impact of a comet on earth. Although once considered a unique event by earth scientists, evidence has been unearthed that a number of the mass‐extinctions in the history of life on earth were caused by impacts of celestial bodies. It is an open empirical question whether absolutely unique events exist or not, but so far none has been identified by earth science.

[6] Turner (2005) arrives at the same conclusion, namely that causal explanations are underdetermined by the data rather than overdetermined. His line of reasoning is different, however.