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Earth Science Chapter 17 PLATE TECTONICS

Continental Drift, Plate Tectonics, and Volcanoes.
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Wegner
Scientist who came up with the theory of Continental Drift.No one believed at first, because he couldn't explain how the continents moved.
Continental Drift
The theory that states that all Earth's continents were once a single landmass called Pangaea.
Pangea
The one single landmass scientists believe existed before the continents broke apart.
Harry Hess
The scientist that came up with the theory of seafloor spreading.
Seafloor Spreading
The theory that new ocean crust is formed at ocean ridges and destroyed at deep-sea trenches.
Thoery of Plate Tectonics
The theory that says Earth's crust and rigid upper mantle are broken into enormous slabs called plates.
Plate Boundaries
Areas where tectonic plates interact.
Convergent Boundaries
Places where tectonic plates are moving towards one another.
Divergent Boundaries
Places where tectonic plates are moving apart from one another.
Transform Boundaries
Places where 2 plates slide past each other horizontally.
Subduction
When plates meet and 1 of the 2 plates is is forced benath the other.
Rift Valleys
Divergent boundaries that occur on land
Viscosity
The internal resistance to flow (how "sticky" a substance is).
Andesitic Magma
Forms from crust being sub-ducted, pushed down, into the Earth's mantle. This magma type has an intermediate viscosity.
Basaltic Magma
Forms from rock in the upper mantle melting. This magma type has a low viscosity.
Rhyolitic Magma
Forms from molten material rising and mixing with the crust above it. This magma type has a high viscosity
Calderas
Large Craters
Shield Volcanoes
These produce mountains with a broad, gently sloping side and a nearly circular base.
Cinder-Cone Volcanoes
These volcanoes have steep sides and are generally small.
Composite Volcanoes
These are much larger then Cinder-Cone Volcanoes.
Tephra
Rock fragments thrown into the air during an eruption.
Pyroclastic Flow
Rapidly moving tephra and volcanic ash that moves down the volcano.
Hot Spots
Volcanoes found far away from plate boundaries.
Gondwanaland or Gondwana
Large continent in the southern hemisphere. Included the land now found in South America, Africa, Antarctica, India, & Australia
Early Evidence for Plate Tectonics
Jigsaw-like fit of Africa and South America (early mapmakers), matching rock formations on opposite sides of the Atlantic Ocean, same fossils on multiple continents, fossils indicating had different climate in past
Kannemeyerid
Land-dwelling animal found on different continents and could not swim to get there.
Mesosaurus
Freshwater reptile that could not have swum ocean, yet is found on different continents.
Glossopteris
Fern that grew in temperate climates, similar to our climate. Yet, fossils of the fern have been found in cold Antarctica and equatorial India.
Past Climate Based on Coal
Coal, made from swamp plants, has been found in Antarctica & indicates Antarctica was warmer at one time. Was it closer to equator?
Magnetometer
Measures small changes in magnetic fields
Paleomagnetism
Study of Earth's magnetic field, based on magnetic iron of basalt on the ocean floor. The iron lines up and "points" in the direction of the Earth's magnetic field when the magma cooled and formed rock.
Magnetic Reversal
Change in Earth's magnetic field. The iron in the basalt on the ocean floor indicate the Earth's magnetic field has reversed several times.
Magnetic Symmetry
Opposite sides of an ocean ridge have mirror-image patterns of magnetic reversals.
Isochron
Line on a map that connects points of equal age that were formed at the same time. Isochron maps have been used to map the age of the ocean floor - Figure 17-11 p.453
Convection (As it relates to plate tectonics)
Transfer of energy by the flow if a heated material. Convection currents in the asthenosphere (soft, plastic-like part of mantle) are thought to cause plate movement. Convection cycle rises at the mid-ocean ridges of divergent boundaries and sinks at the deep-sea trenches of convergent bondaries.
Folded (Very High) Mountains
Extremely high mountains formed when 2 continental plates converge (collide). Because the continental plates have similar density there is no subduction and plates are crumpled & forced up instead.
Island Arc
Formed above an oceanic-oceanic convergent boundary when volcanoes become tall enough to break the surface of the water. Examples: Aleutian Islands, Japan, Phillipines
Deep Sea Trench
Formed at convergent boundaries when subduction occurs and the more dense oceanic plate slips under another plate. The deepest one is by the Mariana Islands.
Rift Valley
Divergent boundary on lad where continental crust begins to separate or "tear apart"
Ocean Ridge
Divergent boundary in ocean where seafloor spreading occurs as magma rises, cools, forms new rock, forcing the 2 plates apart.
Subduction
When one plate is forced to sink below the other. The plate that sinks does so because it is more dense.