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Continental Drift Theory Proposed
Alfred Wegener noticed that the continents somewhat "fit together." He called this super continent "Pangaea." In 1912 (exact date unknown) he proposed the continental drift theory. However he lacked one important explanation, how they broke apart. So the theory was disapproved by many scicentists. This theory, even though disapproved, opened the gate to the discovery of plate tectonics. -
Sonar Technology 1920's
The ocean floor was thought by many to be a falt featureless surface. However sonar devices used to measure depth, showed otherwise. Scientist soon learned that the ocean floor had many mountain chains and deep mid-ocean ridges. -
Arthur Holmes
In 1929 geoloigist Arthur Holmes came up with an explanation for Wegener's theory. He insisted that heat convection in EArth's mantle caused Pangea to split apart. -
Harry Hess and Robert Dietz
Harry Hess came up with the idea that oceanic crust forms along ocean ridges and spreads out across the ocean floor from there. Robert Dietz named this thought Sea-Floor Spreading. -
Earthquake Sensors
In 1963, sensors were installed to track earthquake activity. These sensors showed that most earthquake and volcanic activity happened at the edge of Earh's plates. -
Glomar Challenger
In 1968 the vessel named the Glomar Challenger set out on an exploration of a mid-ocean ridge between South America and Africa. Samples they collected showed that rocks closer to the ridges were younger than the rocks fatrher away. This shows evidence of sea-floor spreading. -
Modern Plate Tectonics
The idea of Plate Tectonics is that the Earth is made up of 6 large plates. These plates are constintly moving about 5 cm per year. Earthquakes and volcanic activity are more likely around the edges of these plates because of them rubbing together. When these plates diverge they pull apart causing mid-ocean ridges over time. THis could be an explanation for Wegeners idea of continental drift.