plate tectonic

• Wegener's continental drift hypothesis stated that the continents had once been joined to form a single supercontinent.
• Mantle plumes are masses of hotter-than-normal mantle material that ascend toward the surface, where they may lead to igneous activity.
• Wegener proposed that the supercontinent, Pangaea, began to break apart 200 million years ago and form the present landmasses.
• The Continental Puzzle is evidence for continental drift.
• Fossil evidence for continental drift includes several fossil organisms found on different landmasses.
• Rock evidence for continental exists in the form of several mountain belts that end at one coastline, only to reappear on a landmass across the ocean.
• Earth’s major roles include the lithosphere, which is the uppermost mantle along with the overlying crust, and the asthenosphere, which is the layer below the lithosphere.
• A plate is one of numerous rigid sections of the lithosphere that move as a unit over the material of the asthenosphere.
• Divergent boundaries, also called spreading centers, are the place where two plates move apart.
• Convergent boundaries form where two plates move together.
• Transform fault boundaries are margins where two plates grind past each other without the production or destruction of the lithosphere.
• Oceanic ridges are continuous elevated zones on the floor of all major ocean basins, representing divergent plate boundaries.
• Rift valleys are deep faulted structures found along the axes of divergent plate boundaries, which can develop on the seafloor or on land.
• Seafloor spreading produces new oceanic lithosphere.
• When spreading centers develop within a continent, the landmass may split into two or more smaller segments, forming a rift.
• A subduction zone occurs when one oceanic plate is forced down into the mantle beneath a second plate.
• Examples of convergent boundaries include the Aleutian, Mariana, and Tonga islands.
• Oceanic convergent boundaries are where two plates collide, subducting plates contain continental material, and continental convergent boundaries can produce new mountain ranges, such as the Himalayas.
• At a transform fault boundary, plates grind past each other without destroying the lithosphere, and most join two segments of a mid-ocean ridge.
• Paleomagnetism is the natural remnant magnetism in rock bodies, which can be used to determine the location of the magnetic poles at the time the rock became magnetized.
• The discovery of strips of alternating polarity, which lie as mirror images across the ocean ridges, is among the strongest evidence of seafloor spreading.
• Scientists found a close link between deep-focus earthquakes and ocean trenches, and the absence of deep-focus earthquakes along the oceanic ridge system was shown to be consistent with the new theory.
• The data on the ages of seafloor sediment confirmed what the seafloor spreading hypothesis predicted, and the youngest oceanic crust is at the ridge crest, and the oldest oceanic crust is at the continental margins.
• A hot spot is a concentration of heat in the mantle capable of producing magma, which rises to Earth’s surface, and the Pacific plate moves over a hot spot, producing the Hawaiian Islands.
• Scientists generally agree that convection occurring in the mantle is the basic driving force for plate movement.
• Ridge-push causes oceanic lithosphere to slide down the sides of the oceanic ridge under the pull of gravity, and slab-pull is a mechanism that contributes to plate motion in which cool, dense oceanic crust sinks into the mantle and “pulls” the trailing lithosphere along.
• The unequal distribution of heat within Earth causes the thermal convection in the mantle that ultimately drives plate motion.
• Denser oceanic slab sinks into the asthenosphere.
• Pockets of magma develop and rise.
• Continental volcanic arcs form in part by volcanic activity caused by the subduction of oceanic lithosphere beneath a continent, examples include the Andes, Cascades, and the Sierra Nevadas.
• Two oceanic slabs converge and one descends beneath the other.
• This kind of boundary often forms volcanoes on the ocean floor.
• Volcanic island arcs form as volcanoes emerge from the sea.