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CSHS Plate Tectonics

QuestionAnswer
1947 Research ship finds ocean floor sediment to be thinner than expected.
1950 Ocean mapping discovers great underwater mountain range …mid-oceanic ridge. 50,000km long, 800 km across.
1968 Glomar Challenger collects drill samples….
Youngest ocean crust At ridge
Oldest ocean crust At continental margins
No sample of ocean crust is older than 180 million years
Paleomagnetism Basalt (oceanic crust) contains magnetite, as it cools the crystals align in the direction of the magnetic field.
Paleomagnetism extra Magnetic variations are not random! Recognizable, symmetrical pattern on both sides of Mid-Atlantic Ridge. Normal Polarity – present magnetic field (North is North).
Harry Hess Proposed Mid ocean ridges are places where magma erupts and creates new ocean crust, at trenches ocean crust is sinking and being recycled
Importance of Sea Floor Spreading Hess's Idea - Explained why the Earth does not get bigger. Why there is so little sediment accumulation on ocean floor. Why ocean rocks are younger than continental rocks.
Earthquakes and Volcanoes Distribution most active volcanoes and earthquakes are near plate boundaries (trenches and ridges).
Pacific Ring of Fire surrounds the Pacific Ocean, almost 90% of the world’s earthquakes occur along this boundary as well as volcanic eruptions.
Global Positioning Systems Scientists have used GPS systems and radio telescopes to track precise points on continents. Data collected by repeated measurements have detected relative plate motions of 1-12 cm per year.
Convection currents in the mantle As magma near outer core is heated, it expands and rises. As it nears the crust, it cools and condenses moving in a circular motion.
Slab Pull and Slab Push As newly formed oceanic crust moves away from the ridge, it cools and becomes dense. Eventually, the cold slab becomes denser than the Earth layers below it and begins to sink. The sinking slab pulls the trailing plate along.
Created by: kauffy
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