Plate Tectonics

Theory of Plate Tectonics Theory of Plate Tectonics-Theory that states the earth’s crust is broken into plates that float on lower mantle Theory combines the theories of continental drift and sea floor spreading It states how and why continents move Continents move because they are carried along on moving plates

Continental Drift Continental Drift-Idea that states that continents were once a giant landmass, and broke into pieces that moved to the positions they are in today A continent is a large landmass Pangaea-giant landmass that split apart to form today’s continents

Crustal Plates Crustal Plates-large pieces of the solid part of the earth Most scientist think that the crust of the earth and solid part of the mantle are broken into crustal plates Most plates are made up of oceanic and continental crust Largest plate is the Pacific plate

Floating Plates Crustal plates float on the lower part of the mantle Part of the mantle is made up of rock that flows like thick liquid Continents and oceans are carried on plates

Formation of New Sea Floor Sea-floor spreading-process that forms new sea floor. Oceanic crust near the mid-ocean ridge is younger than ocean crust farther away Magma cools forming a new crust on both sides of the ridge and pushes the sea floor out

Evidence of Sea Floor Spreading The earth has a magnetic field The magnetic field of the earth has changed throughout the earth’s history Some minerals have magnetic properties On sea floor there are stripes of rock with magnetic particles pointing north and magnetic particles pointing south

Mid-Ocean Ridges Mid-Ocean Ridge-Underwater mountain chain Some of the largest mountain ranges and tallest mountains are located under the ocean Peaks of some of these mountains form islands Mid-Atlantic Ridge runs down the middle of the Atlantic Ocean

Subduction Zone Subduction Zone-Place where old crust is pushed down into a trench Older oceanic crust is pushed down into the mantle Mantle-layer of the earth below the crust There is volcanic activity near subduction zones Ring of Fire around the Pacific Ocean has many subduction zones

Rift Valley Rift Valley-Deep crack running down the center of the mid-Atlantic ridge Magma pouring out of the rift hardened and formed a broad valley with steep sides Scientist discovered that a lot of earthquakes and volcanic activity take place along mid-ocean ridges

Trenches Trench-long, V-shaped valley Trenches are the deepest parts of the ocean Most trenches are found in the Pacific Ocean Located along the coasts of continents and near strings of islands Many trenches are along the Ring of Fire

Disappearing Crust Scientist believe that old oceanic crust is pushed into ocean trenches where it is changed to magma If the crust were not being destroyed, the earth would be getting bigger Crust pushed deep enough, the rocks of the crust melt

Convection Currents Convection Currents-Movement of gas or liquid caused by changes in temperature Warm air rises and cool air sinks to take its place Hot water rises and cool water at the top ends up sinking

Inside the Mantle Mantle rock close to the core, or center of the earth, is hot Scientist believe that giant convection currents in the earth’s mantle cause the movement of crustal plates Hot mantle rock rises and cooler rock sinks deeper in the mantle

The Restless Earth Crustal plates move in different ways Crustal plates move toward each other, move apart, or slide past each other Oceanic crust is pushed under continental crust Oceanic crust is pushed into the mantle

Earthquakes Many earthquakes are caused by the movement of plates at a fault Two crustal plates slide past each other Movement of crustal plates sliding past each other cause the earthquake San Andreas Fault-California

Mountain Building Mountains are formed when two plates collide and oceanic crust pushes down under continental crust Two crustal plates carrying continents may collide without one plate being pushed down under the other Himalaya Mountains are formed from this method

Volcanoes Magma Chamber-Underground pocket of molten rock At subduction zones, friction between oceanic crust and the continental crust produces great heat Heat melts the rocks in crust and forms magma When magma reaches surface volcano forms