“The most important ingredient in the formulation of the sea floor spreading and the later plate tectonic theories was the knowledge of the existence of the mid-ocean ridge system.” -L. Morley Carrie Welker Mason Edwards History of Mid-Ocean Ridges: Role in the Development of Plate Tectonics

Pre-Plate Tectonics Questions driving the theories: Why do continents like South America and Africa look like they fit together? Why are there corresponding rock formations and fossil assemblages on the edges of continents? How do mountains form? Theories: Contraction Theory – Edward Suess ( ) Geosynclines – James Hall ( ) Continental Drift – Alfred Wegener ( ) No unifying theory of earth science!

Mid-Ocean Ridges: Pre World War II 1620 –Francis Bacon notices how South America and Africa “fit” together 1855 – Bathymetry from U.S. Navy proves mountains in the mid-Atlantic 1912 – The Origins of Continents by Wegener suggests continental drift. WWI –Development of sonar will aid in sea floor mapping 1920s-30s –Mechanism of continental drift hotly debated. What could cause lateral motion of continents?

WWII – Extensive mapping of sea floor magnetics 1954 – Benioff zones at continental margins 1956 – Magnetic field orientation rock record noted Mid-Ocean Ridges: World War II (Benioff, 1954)(

– Hess suggests sea floor spreading 1963 – Vine & Matthews correlate magnetic anomalies to sea floor age 1965 – Wilson differentiates between MOR transcurrent and transform faults 1975 – Uyeda correlates plate velocity with subducted slab “quantity” Mid-Ocean Ridges: Post 1960 (Synthesis) (Reproduced from Uyeda, 1978)