“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 WelkerMason 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 (1831-1914)• Geosynclines

– James Hall (1811-1889)• Continental Drift

– Alfred Wegener (1880-1930)

No unifying theory of earth science!

1900 1950 2000

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

1900 1950 2000

Mid-Ocean Ridges: World War II - 1960

(Benioff, 1954)(http://www.clas.ufl.edu)

1900 1950 2000

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Plate Velocity(Centimeters per year)

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1962 – 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)