PLATE TECTONICS

A. Introduction

Today plate tectonics is a mature theory but it is remarkably recent as scientific theories go.  Most of the key elements of the theory have been formalized within the last 30 years but the idea that the continents had moved to their present positions from somewhere else is a very old idea.

B. Mapping the sea-floor and paleomagnetism (note: Chapter 3 of CP&M was not assigned as reading for this topic but forms good background for some of the discussion of plate tectonics and some references to figures refer you to chapter 3)

C. Great faults and deep earthquakes in the Pacific

D.  A Mature Theory (a 'Paradigm') and Driving Forces

In 1967 two geophysicists at Cambridge University in the U.K. (MacKenzie and Morgan) formalized the theory of plate tectonics:

Within the span of about ten years, continental drift had gone from an hypothesis to a theory with predictive power about the large-scale dynamics of the Earth. The principal conceptual objection to continental drift was overcome. The continents did not plow through the ocean basin but were instead just more buoyant (less dense) lithosphere that was attached to the more dense oceanic lithosphere, forming large plates of lithosphere that were riding on the softer/ductile mantle asthenosphere. Today we recognize about a dozen discrete lithospheric plates (CP&M p. 75, Fig. 4.1) bounded by the three types of plate boundaries (divergent, convergent, transform) that we have discussed.

We accept that this is our working theory of the dynamics of the outer Earth and plate tectonics contributes to and has implications for many other phenomena and processes occurring on and within the earth including:

Such an overarching framework within science is sometimes called a 'paradigm'.  Much work since the development of plate tectonic theory has been a filling in many of the details of plate tectonics and in trying to undertstand how plate processes are involved in many other geologic processes, including trying to understand the forces that drive the plates.