Plate Tectonics

What Did The Earth Look Like In The Past?

CONTINENTAL DRIFT THEORY Alfred Wegener - 1912 - 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 GLOSSOPTERIS - G Fossil plant /Similar climate LYSTROSAURUS - L A small reptile R C/W ROCK CLUE - R Rock structures are similar types & ages R CLIMATE - C Warm weather plants R GL G GL G L GL G R R L M GLACIERS - GL Glacial deposits & Rock surfaces scoured & polished by glaciers G M GL L G MESOSAURUS - M Freshwater/Land reptile

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. 6 5 4 3

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. PLATE TECTONICS 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.

Divergent plates spread apart from each other, creating new 1. 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. 5. SEAFLOOR SPREADING 3. 2. 4. 6.

Names of Plates

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. PLATE TECTONICS

North America and Eurasia 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

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

Plates Move Toward Each Other This is called Convergence – these are destructive boundaries since they deform the plates 19. Convergent 21. Folded Mountains 15. Subduction 20. Continent/Continent 14. Ocean/Continent 13. Convergent 17. 16. 18. Andes Mountains 10. 11. Ocean/Ocean Subduction 8. 9. 12.

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

is created when two plates collide into each other. When 7. 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.

Mountain Formation Rock parts pulled Sierra & Teton Range Apart from faults Sierra & Teton Range Mountain Formation Rock layers folded Or compressed Appalachians Plates sink and Melting occurs Lava piles up From magma Hawaiian Islands Rocky & Adirondack Forces in Earth Push on crust

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

26. 23. Transform 24. Shearing TRANSFORM FAULT 25. 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.

FAULTS are fractures or break in earth’s crust - movement has taken place - rock strata layers do not match - create mountains- Niagara Falls. Blocks are pulled apart overlying block moves down the fault plane. A spreading zone. Sierra Nevada's Foot Wall Hanging Wall Squeezing or compressing Blocks are pushed together Moves up the fault plane. Himalayas Mts. - India Foot Wall Hanging Wall Transform - strike - slip fault - a lateral fault Slide past each other. San Andreas, CA.

CONVERGENT CONVERGENT LAND OCEAN DIVERGENT

Earthquakes, Volcanoes & Mountains

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