This innovative book uses the story of how a modern science achieved its present shape and focus to examine the nature of scientific change and its philosophical and social analysis. The 'modern revolution in geology' of the 1960s and 1970s saw the triumph of the global theory of plate tectonics; a decisive turning point in fifty years' controversy and competition, first sparked in 1912 by Wegener's proposal of continental drift. Here, Professor Le Grand interweaves a history of this episode of scientific change with reflective discussions of its historical, philosophical and social circumstances, and of the development of science more generally. The approach of the book is exploratory rather than dogmatic. The reader is encouraged to be an active participant - to use the historical narrative to understand and criticize some of the more recent, influential ideas about science and scientists; to draw conclusions and especially to pose questions about how and why changes occur in scientific knowledge and practice. The book may be read as an introduction to and history of central concepts of modern geology; as a social and intellectual account of a major revolution in science; and as an incisive commentary on and constructive criticism of several interpretations of the nature of science and the process of scientific change. Its structure, content and approach make it accessible to general readers, yet at the same time of interest to professionals and students of geology and of the history, philosophy and sociology of science.