INTRODUCTION

During my lifetime, the earth sciences have undergone a scientific revolution, as significant as the discovery that matter is composed of atoms containing a nucleus and electrons, or the discovery of DNA. This is the theory of plate tectonics, which completely knocks the props out from what I was taught in graduate school. This theory provides an explanation of why Earth, probably unique among the inner planets, is afflicted with earthquakes. I lived through this paradigm shift, and I now regard it as one of the most thrilling scientific adventures in my own life. Some of the major discoveries in this revolution were made by graduate students who were my own age.

THE PARADIGM SHIFT TO PLATE TECTONICS

Up until World War II, most geologists had no doubt that continents and ocean basins had always been where we now find them, although Alfred Wegener, a German meteorologist, had postulated the theory of continental drift as early as 1912 in the first edition of his book, The Origin of Continents and Oceans. Wegener had observed that you could close up the Atlantic Ocean, and the continents would come back together, like fitting together the pieces of a jigsaw puzzle. In addition, after fitting the puzzle pieces back together into a supercontinent Wegener called Pangaea, the picture on top of the jigsaw puzzle matched. Fossil plants and shallow-water animals on one side of the puzzle were found to be similar to those on the other side, even though the two sides are now separated by thousands of miles of ocean floor. Wegener argued that these plants and animals could not have made their way from one continent across the deep ocean to the other.

Wegener's idea was rejected by the scientific establishment of Europe and North America, but it was attractive to geologists in the Union of South Africa, especially Alexander du Toit. He pointed out that the geology of mountain ranges in South Africa is very similar to the geology of mountain ranges in South America after the continents had been fitted back together.