Chapter 7 Chapter 7

Section 1: Continental DriftSection 1: Continental Drift

Section 2 : Sea Floor SpreadingSection 2 : Sea Floor Spreading

Section 3: Plate TectonicsSection 3: Plate Tectonics

Section 1 Continental DriftSection 1 Continental Drift

• Alfred Wegener– (1880-1930)– Proposed hypothesis of continental drift– Pangaea

Evidence to support C.D.Evidence to support C.D.

• Continents appear to fit together like a puzzle

• Similar fossils have been found on different continents

• Remains of warm climate plants in arctic zones and Arctic clues in tropical zones

• Similar rock structures found on different continents

Section 2: Seafloor SpreadingSection 2: Seafloor Spreading

• Magma below Oceanic crust pushes upward and outward forcing the crust into large underwater mountain ranges.

• Mid Ocean Ridges

Evidence for S.F.SEvidence for S.F.S

• A theory– Has been proven to occur

• Rocks increase in age as one moves away from the mid-ocean ridges.

• Continents are measure farther apart by 1 or 2 inches per year

old new

Section 3: Theory of Plate Section 3: Theory of Plate TectonicsTectonics

• Combines the hypothesis of continental drift with the theory of sea floor spreading.

• Earth’s crust and upper mantle broken into plates.

• Shift on layer of molten rock.

Earth’s platesEarth’s plates

• Lithosphere– Earth’s crust and upper mantle– Layer that shifts

• Asthenosphere– -like layer

of mantle.

Earth’s crustEarth’s crust

• Continental crust– Thick– Less dense– Older– Forms land

• Oceanic crust– Thin– Dense– Younger– Forms ocean bottom

Plate BoundariesPlate Boundaries

• Divergent– Where 2 plates move apart– Sea floor spreading!– Mid-Atlantic ridge– Rift Valley

Plate Boundaries contd.Plate Boundaries contd.• Convergent Boundary

– Where 2 plates move together.– Oceanic / Continental plate collision– Subduction

zone.– Volcanic

Mtns.– Trench

Convergent Boundaries contd.Convergent Boundaries contd.

• Continental / Continental crust collision– Forms mountains– India plate moving north / Eurasian plate

moving south.• Himalayan Mountains

Himalayan MountainsHimalayan Mountains

• Oceanic/Oceanic convergent collision.

• Creates a trench

• Both subducted, but one more than the other

Transform BoundariesTransform Boundaries

• 2 plates sliding past each other

• Strike-slip faults

• Can move in different directions or the same direction at different rates.

• San Andreas Fault in California.– Earthquake zone

Transform BoundaryTransform Boundary

Causes of Plate movement.Causes of Plate movement.

• Convection Currents– The heating, rising, cooling, and falling cycle

of molten rock in the earth’s mantle.

Earth’s Plates and movement.Earth’s Plates and movement.

Tectonic Plates and Land Forms.Tectonic Plates and Land Forms.