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Discoveries and ideas of Harry Hess and Alfred Wegner
Transcript of Discoveries and ideas of Harry Hess and Alfred Wegner
Harry Hess took measurements of the seafloor with the sounding equipment he had.He discovered what looked like mountains with flat tops. Hess described how the hot magma rose from under the crust and it cooled and expanded and pushed the plates apart.
Sea Floor Spreading
Sea-floor spreading is the process in which the ocean floor is extended when two plates move apart. As the plates move apart, the rocks break and form a crack between the plates. Earthquakes occur along the plate boundary. Magma rises through the cracks and seeps out onto the ocean floor like a long, thin, undersea volcano.As magma meets the water, it cools and solidifies, adding to the edges of the sideways-moving plates. As magma piles up along the crack, a long chain of mountains forms gradually on the ocean floor. This chain is called an oceanic ridge.
Alfred Wegener is a meterologist.He says the earths surface is constantly changing because the continents were moving. His idea is of drifting continents. Wegener's ideas became generally accepted among experts. He could not prove his theory of the outer, solid shell of the earth is broken up into rigid plates. Wegener is the father of plate tectonics.
Plate tectonics is the theory that the outer rigid layer of the earth (the lithosphere) is divided into about a dozen " plates" that move across the earth's surface relative to each other, like slabs of ice on a lake.The movement of the plates is driven by convection currents in the mantle so the plates are continuously pushing against each other. Earthquakes, and mountain building happens at the edge of plates.There are three kinds of plate boundaries.
Divergent boundaries are where plates separate from each other, and magma oozes up from the mantle into the crack making the ocean wider. This is known as sea floor spreading.
Convergent boundaries are where plates come together, but to do so one of the plates must dive below the surface into the mantle along a subduction zone. Convergent boundaries produce mountain chains of very large, explosive volcanos (composite type).
And transform boundaries where plates slide past each other, ideally with little or no vertical movement. Most transform boundaries are below sea level and so not easy to see. The San Andreas fault in California is a transform boundary.