Plate Tectonics

What Did The Earth Look Like In The Past?

CONTINENTAL DRIFT THEORY Alfred Wegener developed theory of a large land mass called Pangaea (means all land). The ocean was called Panthalassa. He thought Pangaea broke apart and floated on the ocean floor due to earth’s rotation. Evidence of proof: fossils of plants & animals, rocks, glacial clues, matching climate and continents fitting together like a puzzle. Theory was ignored because there was no explanation of how, when, or why these changes took place.

Evidence of Continental Drift MESOSAURUS - M Freshwater/Land reptile G G GLOSSOPTERIS - G Fossil plant /Similar climate R M M G G G CLIMATE - C Warm weather plants GLACIERS - GL Glacial deposits & Rock surfaces scoured & polished by glaciers GL C/W GL ROCK CLUE - R Rock structures are similar types & ages R R R R LYSTROSAURUS - L A small reptile L L L

Principle of Uniformitariantism - states that the processes we see changing Earth’s surface today are the same as those that changed it in the past. Principle of Superposition - states that layers of sedimentary rock near the surface are younger than layers of rock deeper down, unless something Has disturbed the layers. Unconformity - is a place where rock layers are missing

PLATE TECTONICS In 1968, scientists aboard the research ship Glomar Challenger drilled into the seafloor for rock samples. They discovered that the youngest rocks were located on the mid-ocean ridge in the Atlantic Ocean. The rocks became older as they moved farther away from the ridge. This gave evidence to the theory of seafloor spreading that was suggested by a Princeton University scientist, Harry Hess. Hess was on a Navy vessel in WW II, mapping the ocean floor with a fathometer - a type of sonar that used echo sounding to help ships know where the bottom of the ocean floor was. He proposed that hot, less dense material below the crust rises toward the surface at the mid ocean ridges, flowing sideways, carrying the seafloor away from the ridge in both directions.

The Earth’s crust appears to be broken into pieces like a puzzle, which are called plates. These rigid plates are being moved by the convection currents in the hot, molten mantle. The plates spread apart, collide or slide past each other, causing earthquakes, volcanoes, mountains and ridges. The plates can move 2 to 15 centimeters each year.

DIVERGENT CONVERGENT OCEAN LAND

Plates Move Away From Each Other This is called Divergence – these are constructive boundaries since they produce new land Africa and Arabia North America and Eurasia Mid-Atlantic Ridge

Divergent plates spread apart from each other, creating new crust. Hot, molten magma rises to the surface of the ocean floor, pushing the floor outward. On the Mid- Atlantic Ridge, the North American plate is moving away from the Eurasian and the African Plates. This process is making the Atlantic Ocean larger. The Great Rift Valley in eastern Africa is becoming a divergent plate boundary. Iceland is also. When new seafloor is created by this plate movement, the magma cools quickly, forming a crust made of basalt rock. This creates a very heavy, dense crust, even though it is only 3 miles thick. SEAFLOOR SPREADING

Rift Valley – if the land is above water Sea Floor Spreading – when the land is below water Divergence – Moving Apart

Plates Move Toward Each Other This is called Convergence – these are destructive boundaries since they deform the plates Continent/Continent Ocean/Continent Ocean/Ocean Subduction Convergent 14. Subduction Andes Mountains Convergent Folded Mountains 21.

Convergence – Moving Together Trenches Mountains Structural Mountains Volcanic Mountains 22.

A convergent boundary is created when two plates collide into each other. When this occurs, mountains and/or volcanoes are created and earthquakes can happen. When the heavier oceanic floor collides into the lighter continental crust, the continental crust is pushed over the oceanic crust. The oceanic crust “dives” under the continental crust creating a subduction zone. Land is lost in this area. The Pacific Ocean is getting smaller because of this process. 7.

TRANSFORM FAULT This type of boundary occurs where two plates slide past one another. They move in opposite directions or in the same direction at different rates. When one plate slips past another suddenly, earthquakes occur Shearing Transform

Active Movements - Faults One day – Los Angeles and San Francisco will be next to each other

Earthquakes, Volcanoes & Mountains Earthquakes Earthquakes & Volcanoes

Divergent Convergent Transform Sea floor spreading Mid ocean ridge Rift ValleyIceland Mid-Atlantic Ridge Collision of Ocean-ocean Subduction Trench Island arc Convergent Ocean-ocean subduction Volcanic mountains Collision of Continental/ oceanic Trench Andes Mountains Shearing Collision of Continental/ continental Folded mountains Himalaya Mountains Transform fault San Andreas fault

Types of Boundary – convergent, divergent, transform Choices of Motion at Boundary – collision of continental/continental Collision of oceanic/oceanic Collision of continental/oceanic Ocean floor spreading Shearing Subduction Land Features Formed - Island arc Folded mountains Mid-ocean ridge Rift valley Transform fault Trench Volcanic Mountains Actual Examples – Andes Mountains Aleutian Islands Himalaya Mountains Iceland Mid-Atlantic Ridge San Andreas

Names of Plates