Plate TectonicsPlate Tectonics continental driftcontinental drift = at one time earth had one giant = at one time earth had one giant landmass that split apart and drifted to their present landmass that split apart and drifted to their present

positionspositions1. Eduard Suess (Austrian) hypothesized that present 1. Eduard Suess (Austrian) hypothesized that present southern continents had once been joined as a single southern continents had once been joined as a single landmass; named it “Gondwanaland”landmass; named it “Gondwanaland”2. first scientific hypothesis proposed by Alfred Wegner 2. first scientific hypothesis proposed by Alfred Wegner (1912)(1912)3. continents have moved 3. continents have moved horizontally to their current horizontally to their current locationslocations

4. 4. PangaeaPangaea = giant landmass when continents were joined = giant landmass when continents were joined together together

5. 5. PanthalassaPanthalassa = huge ocean that surround Pangaea = huge ocean that surround Pangaea6. rejected because he could not explain 6. rejected because he could not explain a) what forces could move continents and a) what forces could move continents and b) how continents could move without shatteringb) how continents could move without shattering

EVIDENCE FOR CONTINENTAL DRIFTEVIDENCE FOR CONTINENTAL DRIFT

1. similarities in coastlines of continents1. similarities in coastlines of continents

2. fossil clues2. fossil clues

a. similar fossils found on different continentsa. similar fossils found on different continents

b. similar fossils found in areas with different climatesb. similar fossils found in areas with different climates

Ex: Mesosarus = South America and AfricaEx: Mesosarus = South America and Africa

Glossopteris = Africa, Australia, India, South Glossopteris = Africa, Australia, India, South America, and Antarctica America, and Antarctica

3. geologic evidence3. geologic evidence a. age and type of rocks in coastal regions of widely a. age and type of rocks in coastal regions of widely separated areas matched closelyseparated areas matched closely b. similar rock structures are found on different b. similar rock structures are found on different continentscontinents c. mountain chains that ended at coastline of one c. mountain chains that ended at coastline of one continent seemed to continue on landmasses across continent seemed to continue on landmasses across oceanocean

Ex: Appalachian Mountains of Ex: Appalachian Mountains of US similar to mountains in US similar to mountains in Greenland and western EuropeGreenland and western Europe

4. climate clues4. climate clues a. layers of debris from glaciers in southern Africa, a. layers of debris from glaciers in southern Africa, South America, India, & AustraliaSouth America, India, & Australia b. coal deposits in United States, Europe, Antarctica, and b. coal deposits in United States, Europe, Antarctica, and Siberia indicate tropical or subtropical swamps Siberia indicate tropical or subtropical swamps covered land oncecovered land once5. puzzle like fit of continents5. puzzle like fit of continents

6. 6. sea-floor spreadingsea-floor spreading = states that new ocean crust is = states that new ocean crust is formed at ocean ridges and destroyed at deep-formed at ocean ridges and destroyed at deep-sea trenchessea trenches

a. a. Mid-Atlantic RidgeMid-Atlantic Ridge = undersea mountain range with a = undersea mountain range with a steep, narrow valley running down its centersteep, narrow valley running down its center

b. b. mid-ocean ridgesmid-ocean ridges = system of undersea mountain = system of undersea mountain ranges that wind around earthranges that wind around earth

Mid-ocean ridge

c. ocean floor was very young compared to age of c. ocean floor was very young compared to age of continental rockscontinental rocks

1) oldest seafloor rock = 150 million years1) oldest seafloor rock = 150 million years 2) oldest continental rock = 4 billion years2) oldest continental rock = 4 billion years 3) composed of bands with youngest rocks at mid-ocean 3) composed of bands with youngest rocks at mid-ocean

ridgeridge 4) older rocks are pushed away from ridge toward deep-4) older rocks are pushed away from ridge toward deep-

sea trenchsea trench

d. d. Harry HessHarry Hess = proposed that the ocean floor was moving = proposed that the ocean floor was moving away from both sides of ridge away from both sides of ridge

1) as it moved away, rising magma replaced it creating 1) as it moved away, rising magma replaced it creating new ocean as it coolednew ocean as it cooled

2) if ocean floor was moving, the continents might also 2) if ocean floor was moving, the continents might also be movingbe moving

e. movement named sea-floor spreading by e. movement named sea-floor spreading by Robert DietzRobert Dietz f. observation of ocean-floor sediments shows that f. observation of ocean-floor sediments shows that

thickness of sediment layer increases with distance from thickness of sediment layer increases with distance from ocean ridgeocean ridge

7. 7. paleomagnetismpaleomagnetism = study of magnetic record in rocks = study of magnetic record in rocks a. iron-bearing minerals in rock become permanently a. iron-bearing minerals in rock become permanently magnetically oriented as rock hardens and points to magnetically oriented as rock hardens and points to

northnorth b. rocks with magnetic orientation pointing south b. rocks with magnetic orientation pointing south

indicate a reversal in earth’s magnetic fieldindicate a reversal in earth’s magnetic field c. c. magnetic reversalmagnetic reversal = change in Earth’s magnetic field = change in Earth’s magnetic field 1) 1) normal polaritynormal polarity = rocks with magnetic fields = rocks with magnetic fields

pointing north pointing north [same orientation as Earth’s present field][same orientation as Earth’s present field]

2) 2) reverse polarityreverse polarity = rocks with magnetic fields = rocks with magnetic fields pointing south [opposite to present field]pointing south [opposite to present field]

3) found that rocks show many magnetic reversals3) found that rocks show many magnetic reversals

d. magnetic patterns on ocean floord. magnetic patterns on ocean floor 1) showed alternating band of normal and reversed 1) showed alternating band of normal and reversed

magnetismmagnetism 2) stripped patterns of magnetism on one side of ridge 2) stripped patterns of magnetism on one side of ridge were mirrors images of stripped patterns on other sidewere mirrors images of stripped patterns on other side 3) 3) isochron mapsisochron maps = used to show age of ocean floor = used to show age of ocean floor

based on magnetic fieldsbased on magnetic fields 4) 4) isochronisochron = line on map that connects points that have = line on map that connects points that have

same age same agee. e. magnetometermagnetometer = detects, = detects,

measures, and records measures, and records presence of weak presence of weak magnetic fieldsmagnetic fields

THEORY OF PLATE TECTONICSTHEORY OF PLATE TECTONICS

1. 1. tectonicstectonics = study of formation of features in earth’s crust = study of formation of features in earth’s crust

2. 2. plate tectonicsplate tectonics = theory that combines ideas of = theory that combines ideas of continental drift and seafloor spreading to explain continental drift and seafloor spreading to explain formation of crust, its movements, collisions, and formation of crust, its movements, collisions, and destructionsdestructions

3. types of earth’s crust: oceanic crust and continental crust3. types of earth’s crust: oceanic crust and continental crust

4. 4. lithospherelithosphere = oceanic and continental crust and rigid = oceanic and continental crust and rigid upper mantle upper mantle

a. thin outer shell of eartha. thin outer shell of earth b. less dense than material below which causes b. less dense than material below which causes movement of plates movement of plates = broken into sections= broken into sections 1) have identified 30 so far1) have identified 30 so far 2) interact together to create major surface features2) interact together to create major surface features

a) move toward each other and collidea) move toward each other and collide b) moving apartb) moving apart c) slide past one anotherc) slide past one another

c. composed of granite, basalt or peridotite, solidc. composed of granite, basalt or peridotite, solid

5. 5. asthenosphereasthenosphere = layer of solid rock that slowly flows = layer of solid rock that slowly flows when under pressurewhen under pressure

a. has a. has plasticityplasticity = characteristics of a solid, but also = characteristics of a solid, but also flows like a liquid flows like a liquid

b. plates of lithosphere float on topb. plates of lithosphere float on top c. bottom part of upper mantle; made up of peridotitec. bottom part of upper mantle; made up of peridotite

plate boundariesplate boundaries = areas where two plates interact = areas where two plates interact1. can be in middle of ocean floor, around edges of 1. can be in middle of ocean floor, around edges of

continents, or within continentscontinents, or within continents2. not always easy to identify2. not always easy to identify

TYPES OF BOUNDARIESTYPES OF BOUNDARIES1. 1. divergent boundarydivergent boundary = where two plates are moving or = where two plates are moving or

pulling apartpulling apart a. occurs at mid-ocean ridges (on ocean floor)a. occurs at mid-ocean ridges (on ocean floor) 1) 1) rift valleyrift valley = narrow valley formed as plates separate = narrow valley formed as plates separate 2) can form at mid-ocean ridges or where continents are 2) can form at mid-ocean ridges or where continents are

separated by plate movement separated by plate movement 3) those that form on continents could eventually form 3) those that form on continents could eventually form

new ocean basinnew ocean basin b. also called b. also called constructive boundariesconstructive boundaries c. involved in process of c. involved in process of

seafloor spreading and seafloor spreading and formation of new ocean crustformation of new ocean crust

d. usually associated with d. usually associated with volcanic and earthquake activityvolcanic and earthquake activity

2. 2. convergent boundaryconvergent boundary = direct collision of one plate with = direct collision of one plate with another another

a. also called a. also called destructive boundariesdestructive boundaries b. three typesb. three types 1) oceanic crust plate collides with continental crust 1) oceanic crust plate collides with continental crust

plate plate a) a) subduction zonesubduction zone = region where one plate = region where one plate

moves moves under another plate under another plate b) ocean plate is subducted below continental plateb) ocean plate is subducted below continental plate

c) creates deep-sea trenches, form volcanic c) creates deep-sea trenches, form volcanic mountains, earthquakes common mountains, earthquakes common

d) series of volcanoes form d) series of volcanoes form along edge of continental platealong edge of continental plate

Ex: Peru-Chile TrenchEx: Peru-Chile Trench

2) two continental crust plates collide2) two continental crust plates collide a) edges are crumpled and uplifteda) edges are crumpled and uplifted

b) produce large mountain rangesb) produce large mountain ranges c) earthquakes commonc) earthquakes common

3) two oceanic crust plates collide3) two oceanic crust plates collide a) subduction zones present which form deep-sea a) subduction zones present which form deep-sea

trenchestrenches b) formation of b) formation of island arcsisland arcs = chain of volcanic islands = chain of volcanic islands c) earthquake and volcanic activity commonc) earthquake and volcanic activity common Ex: Mariana Trench and Mariana IslandsEx: Mariana Trench and Mariana Islands

3. 3. transform fault boundarytransform fault boundary = where two plates grind past = where two plates grind past one anotherone another

a. occur when two plates move in opposite directions or a. occur when two plates move in opposite directions or same direction at different ratessame direction at different rates

b. plates move past one another horizontallyb. plates move past one another horizontally c. scrape together and move in series of sudden spurts of c. scrape together and move in series of sudden spurts of

activity separated by periods of little or no motionactivity separated by periods of little or no motion d. crust is only deformed or fractured, most occur in d. crust is only deformed or fractured, most occur in

oceansoceans e. earthquakes commonly occure. earthquakes commonly occur

Ex: San Andreas Fault Ex: San Andreas Fault (formed on continent)(formed on continent)

Causes of Plate MotionCauses of Plate Motion1. 1. convectionconvection = transfer of heat through the movement = transfer of heat through the movement

of heated fluid materialof heated fluid material2. 2. convection currentsconvection currents = cycle of heating, rising, = cycle of heating, rising,

cooling, and sinking cooling, and sinking

3. processes in cycle of heating and cooling carrying 3. processes in cycle of heating and cooling carrying plates with itplates with it

a. material in lower asthenosphere become hot and a. material in lower asthenosphere become hot and will be less dense than material above itwill be less dense than material above it

b. material will rise until reaches base of lithosphere b. material will rise until reaches base of lithosphere where it coolswhere it cools

c. when it cools it becomes more dense and starts to c. when it cools it becomes more dense and starts to sink moving horizontally carrying platessink moving horizontally carrying plates

4. subduction zones involve combination of 4. subduction zones involve combination of mechanismsmechanisms

a. sinking region of mantle convection pulls ocean a. sinking region of mantle convection pulls ocean plate down into subduction zoneplate down into subduction zone

b. weight of subducting plate helps pull trailing b. weight of subducting plate helps pull trailing lithosphere into subduction zone = lithosphere into subduction zone = slab pullslab pull

theory of suspect terranestheory of suspect terranes = suggests that continents are = suggests that continents are actually a patchwork of terranesactually a patchwork of terranes

terranesterranes = pieces of lithosphere with its own distinct = pieces of lithosphere with its own distinct geologic history geologic history

1. identifying characteristics1. identifying characteristics a. contains rock and fossils that differ from rock and a. contains rock and fossils that differ from rock and

fossils of neighboring terranesfossils of neighboring terranes b. there are major faults at boundaries of terranesb. there are major faults at boundaries of terranes c. magnetic properties do c. magnetic properties do

not match those of not match those of neighboring terranesneighboring terranes

2. blocks of terranes are carried along on ocean floor by 2. blocks of terranes are carried along on ocean floor by seafloor spreading toward subduction zoneseafloor spreading toward subduction zone

3. terranes are scraped off descending ocean floor3. terranes are scraped off descending ocean floor

4. can form mountains or add to surface area of continent4. can form mountains or add to surface area of continent