From the contracting earth to continental drift: Wegener’s influence on Portuguese and Spanish science textbooks through the twentieth century

Alfred Wegener’s work on continental drift prof oundly influenced the development of geology during the twentieth century. The main objective of this historical research is to explore how Wegener’s hypothesis about the origin of continents and oceans influenced Portuguese and Spanish science textbooks published in the twentieth century. For this purpose, a qualitative method based on the Chevallard’s concept of didactic transposition was used. The didactic transposition of the fundamentals of continental drift, including displacements forces and geographical, geophysical, geological, paleontological, biological, and paleoclimatic arguments used by Wegener to support this hypothesis, was studied in a comprehensive sample of twenty science textbooks published after the publication of Die Entstehung der Kontinente und Ozeane (Wegener 1915). The analysis of textbooks shows that the didactic transposition of continental drift was commonly present in Portuguese and Spanish textbooks beginning in the 1930s, although, with different degrees of development. Science textbooks since the 1950s presented the displacement forces of sial continental blocks proposed by Wegener, namely the centrifugal force of Earth’s rotation and the attractive gravitational force that results from the interaction of the earth with the moon and sun. The geographical, geological, paleontological and biological arguments supporting continental drift were commonly addressed in many science textbooks, followed by the paleoclimatic arguments. The geophysical arguments were briefly addressed in only two textbooks. Many Portuguese and Spanish textbooks also presented critiques of Wegener’s work, mainly focused on the lack of explanation for the origin and nature of forces that could move continents at the Earth’s surface.