THE DYNAMIC CRUST

I. EVIDENCE OF CRUSTAL CHANGE A. Deformed rock structure Tilted strata

Fractured strata

Folded strata

B. Fossil Evidence 1. Marine fossils found at high elevations suggests crustal uplift. 2. Shallow water fossils found at great ocean depths suggest subsidence/sinking.

II. PLATE TECTONICS A. Earth’s Structure 1. Crust 5-35 km thick Density g/cm3 2. Mantle 2900 km thick Density g/cm3 3. Outer Core 2250 km thick Density g/cm3 4. Inner Core Density g/cm km thick

2. Earth’s Surface a.

b. Density of : 1. Ocean (water) 1.0 g/cm3 2. Granite (continental crust) 2.7 g/cm3. 3. Basalt (ocean crust) 3.0 g/cm3. 4. Rigid upper mantle 5. Asthenosphere g/cm3. c. Lithosphere = crust + upper mantle. d. Asthenosphere the plasticlike layer below the lithosphere in Earth’s mantle. e. Thickness of: 1. Continental crust 32 km + 2. Ocean crust 5-8 km.

B. Theory of Continental Drift 1. Alfred Wegner proposed the theory of continental Drift in early 1900’s. 2. About 200 m.y.a. all continents together in landmass called pangea.

3.Evidence for Continental Drift 1) Coastlines of continents fit together South America fits well with Africa like a jig-saw puzzle. 2) Fossil clues – Mesosarrus found in Africa and South America. - Glosopteris found in India, Africa, Australia, Antarctica, S. America.

3. Rock clues: a) Appalachian mountains the same as those in Greenland and western Europe. b) Structure and minerals same between S. America and Africa.

X Mesosaurus fossils M Mountains similar M M M X X G G G G Glossopteris

C. Sea Floor Spreading 1. Ocean floor topography

2. Evidence of spreading 1. As distance from ridge increases, the age of rock increases.

C. Theory of Sea Floor Spreading 1. Earth ’ s lithosphere divided into plates. Key to Major Plates

2. Plate motion – plates “ float ” on the asthenosphere. 3. Direction of movement creates 3 types of boundaries. BOUNDARYMOVEMENTARROWS DivergentAway form each other ConvergentTowards each other TransformLaterally or sideways

4. Types of Plate Boundaries A. Divergent – plates move apart 1. Ocean – Mid Atlantic Ridge. 2. Continental – Rift Valley/Africa.

B. Convergent Plate Boundary – plates collide 1. Ocean/Continent – Pacific plate subducts under S. America.

2. Ocean/Ocean – trenches and island arcs, Aluetian Islands, AK.

3. Continental/Continental – India – Asia collision.

C. Transform Plate Boundaries – San Andreas Fault.

5. Convection currents – the driving force beneath the plates. Hot less dense material rises. Cool more dense material sinks. This convective flow in the mantle carries/moves lithospheric plates.