PLATE TECTONICS IN PORTUGUESE AND SPANISH SCIENCE TEXTBOOKS: FROM THE 1960s TO THE 1980s

Plate tectonics caused a revolution within earth sciences which then was transposed into science textbooks. The main objective of this paper is to explore how plate tectonics influenced Portuguese and Spanish science textbooks published from the 1960s through the 1980s. For this purpose, a qualitative method based on the concept of didactic transposition is used. The didactic transposition of seafloor spreading evidence such as ridges, rifts and trenches, transform faults, seafloor sediments, the age of seafloor basaltic rocks, the magnetic anomalies on the seafloor, the Benioff zones and the subduction process, and also the didactic transposition of the formation of mountains ranges and island arcs, convection currents, plate tectonics concepts, boundaries and motion, and plate tectonics acceptance are studied in a comprehensive sample of science textbooks. The analysis of textbooks shows that the didactic transposition of seafloor spreading, and plate tectonics started mainly in 1970s Portuguese and Spanish textbooks and had a strong development in 1980s textbooks. No major differences were found between the approaches to plate tectonics in similar age Portuguese and Spanish textbooks. At the beginning of the 1970s, textbooks presented partial evidence for seafloor spreading, such as magnetic anomalies and the characteristics of ridges, rifts and trenches. They also addressed convection currents but only those that were related to geosynclines. In the mid 1970s and in the 1980s, textbooks presented more comprehensive evidence of seafloor spreading, by adding didactical transpositions of transform faults, seafloor sediments and the age of seafloor rocks. They also presented in more detail topics such as magnetic anomalies, the Benioff zones, orogenic processes and the tectonic significance of ridges, rifts and trenches. Plate tectonic theory was presented in major textbooks as widely accepted, and discussions about speculative facts or processes were rare.