Plate Tectonics. Earth has distinctive layers - Like an onion

Transcription

1 Plate Tectonics Earth has distinctive layers - Like an onion

2 Earth s Interior Core: Metallic (Iron, Nickel) Inner (hot, solid, dense, Iron, Nickel) Outer (cooler, liquid, less dense)

3 Crust (outermost layer): rigid & very thin Mantle: dense, hot layer of semi-solid rock Core ~ twice as dense as mantle b/c its metallic, not stony

4 Lithosphere: Thin, Rigid, Outer Layer Oceanic Crust (basalt) ~10 km (6 mi) thick Continental Crust (granite) ~55 km (34 mi) thick Asthenosphere warmer, melted (flowing) layer of upper mantle Crust floats on melted layer Like an egg shell, Crust is brittle & can break

5 The Lithosphere is Moving! These rocks were under the sea! Moving plates can cause Earthquakes

6 Early Evidence: Da Vinci (1400 s) F. Bacon (1620) Saw continents fit together like a puzzle How did they move to their present locations?

7 Continental Drift Alfred Wegener (1912) Continents once joined as super continent (Pangea) One world ocean (Panthalassa) Continents broke up 200 mya Still moving!

8 Evidence for Continental Drift 1. Paleontology: Fossils - same age & species (not swimmers) on both sides of Atlantic Tropical species in Antarctica 2. Geologic: Desert sands under rain forest 3. Pacific Ring of Fire ( ): Earthquakes & volcanoes in Pacific associated with C. Drift

9 oceanic trenches Pacific Basin: Zone of frequent volcanic eruptions & earthquakes

10 Patterns of 10,000 earthquakes = Earth is divided into sections

11 Echo Soundings reveal submerged, midoceanic mountain range Seafloor Spreading hypothesis: Ridges = source of new sea floor Spreading Center Mid-Atlantic Ridge Conforms to edges of nearby continents

12 New Sea floor at ridges formed by Convection Hot material rises, cold material falls cool Hot

13 1. Hot magma upwells from mantle 3. Old crust is then pushed away from Mid-Ocean Ridge 2. New ocean crust forms 4. Cold (old) crust is subducted back into mantle at deep sea trenches Heated & recycled

14 Continental Drift & Sea Floor Spreading integrated into Plate Tectonics (1965)

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16 Plates move relative to one another 3 different types of boundaries: 1. Divergent Boundary (apart) 2. Convergent Boundary (together) 3. Transform Boundary (shear)

17 Divergent plate boundary Lithospheric plates move away from each other. EX: Mid-Atlantic Ridge (Atlantic Ocean)

18 Divergent Boundary (constructive): Plates spread & new oceanic lithosphere forms at ocean ridges (Mid-Atlantic Ridge)

19 Pangea was separated by Divergence

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21 Supercontinent Pangaea Eventually fragmented into continents we know today

22 Beginning to crack Basin forms as continents separate

23 Red Sea: Site of a new ocean basin Ethiopian volcano

24 Convergent plate boundary Lithospheric plates move toward each other Ex: Where oceanic Nazca Plate is pushed beneath continental portion of S. American Plate

25 Convergent Boundary (3 types): Plates collide together, Old oceanic crust destroyed -Many earthquakes -Subduction zone a. Oceanic Continental Dense Ocean plate subducts + gravity Magma powers volcano arcs

26 - (Deep) b. Oceanic Oceanic Old plate subducts beneath other Heats, & partially melts (magma) Less dense than surrounding crust = rises to form Volcanic Island Arcs (Japan, Philippines, Caribbean)

27 c. Continental Continental: plates collide, fold, & uplift Indian & Asian plates -> HIMALAYAS One plate may move beneath

28 Transform plate boundary Plates slide past each other. EX: San Andreas fault (California) Pacific Plate slides past North American Plate

29 Transform Boundary Lithosphere isn t created or destroyed Rock shatters Many shallow earthquakes Separates Pacific & North American Plates San Andreas Fault

30 1. Pacific Plate moves over hotspot Hot Spots: Small, Hot Spots long-lasting heat sources 2. Magma rises up &, forms active seamount 3. Grows to form island volcano 4. Plate movement cuts magma source = Volcanism ceases

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32 Paleomagnetism Confirms Plate Tectonics Magnetite: Iron bearing, magnetic mineral present in magma When magma erupts at ridges, magnetite solidifies in cooled rock Spreading centers - symmetrical magnetic bands

33 Earth s magnetic field changes direction (N ~ few 100,000 yrs. (N-S) Convection currents in core Earth s rotation Earth s field like a magnet Compass points N. today, Not always

34 As continents separate, they carry their magnetized rocks with them Rocks permanently magnetized in direction magnetic field pointed at that time (N or S)

35 Pole Direction North South