ERTH 2415 Chapter 3: ERTH chapter 3.docx
14 Mar 2012
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The lithosphere of earth is broken into pieces called plates. These gigantic pieces pull apart during seafloor spreading at divergence zones, slide past at transform faults, or collide at convergences zones. The study of the movements and interactions of the plates is known as plate tectonics. The tectonic cycle: first, melted asthenosphere flows upward as magma and cools to form new lithosphere on the ocean floor. Second, the new lithosphere slowly moves laterally away from the zones of oceanic crust formation on top of the underlying asthenosphere (seafloor spreading). Third, when the leading edge of a moving slab of oceanic lithosphere collides with another slab, the denser slab turns downward and is pulled by gravity back into the asthenosphere (subduction), while the less-dense, more buoyant slab overrides it. Lastly, the slab pulled into the asthenosphere is reabsorbed. It takes 250 million years to complete this cycle. In 1620, francis bacon of england noted the parallelism of the atlantic coastlines of.
