The Theory of an Expanding Earth and the Acceptability of Guiding Assumptions

Abstract

For over two decades plate tectonics has enjoyed a dominant position in the earth sciences. The intellectual grandchild of Alfred Wegener’s theory of continental drift, plate tectonics is the now familiar explanation of continental displacement as the product of lateral movement of rigid lithospheric plates in which continental blocks are embedded. This theory is the direct descendant of Harry Hess’s theory of sea-floor spreading (Hess, 1962), according to which mid-ocean ridges are a source of new crustal material upwelling from the earth’s interior. In Hess’s theory, this new oceanic crust is gradually transported away along crustal ‘conveyor belts’ driven by mantle convection currents, and ultimately dragged back down into the earth’s mantle (subducted) at the trailing edges of these convection currents. Lateral drift of continents occurs as they ride piggy-back along these conveyor belts (see Figure 1).

Most scientists read as little as they can get away with anyway, and they do not like new theories in particular. New theories are hard work, and they are dangerous — it is dangerous to support them (might be wrong) and dangerous to oppose them (might be right). The best course is to ignore them until forced to face them. Even then, respect for the brevity of life and professional caution lead most scientists to wait until someone they trust, admire, or fear supports or opposes the theory. Then they get two for one — they can come out for or against without having to actually read it, and can do so in a crowd either way. This, in a nutshell, is how the plate-tectonics “revolution” took place. (Greene, 1984, p. 753)

I wish to thank the organizers and participants of this conference for helpful comments on an earlier draft of this paper. I am similarly indebted to my colleagues in the College of Charleston Philosophy Department, and to geologists Michael Bevis, Geoffrey Feiss, Kern Fronabarger, and Nancy West.