Plate Tectonics

 TOD: IN (Page: 34)  Brainstorm a list of all you know about Plate Tectonics.  Agenda:  TOD IN  Plate Tectonics Notes Page 35 of Composition Book Page 35 of Composition Book Drawings of plate boundaries

Plate Tectonics and the Ocean Floor  Plate tectonic theory– outermost portion of the Earth is made of plates that move on magma  Alfred Wegener was a German meteorologist who developed the theory of continental drift in 1912  Continental drift- Continents slowly drift across the globe

Evidence of Continental Drift  Pangaea – (pan= all; gaea= Earth) A large landmass that the continents A large landmass that the continents fit together to form fit together to form  Evidence Matching rocks on different continents Matching rocks on different continents Distribution of organisms Distribution of organisms Glacial Activity in now tropical areas Glacial Activity in now tropical areas

The continents fit together

Fossils of same species found on different continents.

More on Continental Drift  As the seafloor spreads the lithosphere moves in sections on the asthenosphere (molten)  On average these tectonic plates move 1- 5 inches/year

More on Continental drift  As new crust is formed old is destroyed  2 types of crust Both types of crust make up the outer layer of earth, called the lithosphere Both types of crust make up the outer layer of earth, called the lithosphere Continental Crust Continental Crust GraniteGranite Lower density than oceanicLower density than oceanic Oceanic Crust Oceanic Crust Igneous rock + basaltIgneous rock + basalt Higher density than continentalHigher density than continental

Continental drift  The crust sits on top of the viscous asthenophere  Viscous?  The asthenosphere is part of the mantle called the upper mantle

Convection  Convection - heat transfer in a gas or liquid  Convection cell is a circular-moving loop of matter (gas or liquid) involved in convection movement

Convection  Convection causes movement in the liquid mantle layer which the crust sits upon  As a result the crust slowly moves on this layer

 TOD: IN (2) (Page: 34)  Venn Diagram Comparing and contrasting hypothesis and Theory  Hypothesis: an idea that can be tested by experiment or observation  Theory: an idea that is the best explanation of many observations and helps to make new predictions

Book Format  Cover: Title  My title “Alfred Wegener’s Report on the Plate Tectonics Hypothesis”  Page 1: Table of Contents Page 2: Evidence to support Page 2: Evidence to support Page 3: Letter to Public Page 3: Letter to Public Page 4: Drawings to show evidence (2) Page 4: Drawings to show evidence (2) Page 5: Letter continued Page 5: Letter continued Page 6: Drawings (2) Page 6: Drawings (2)  Back Cover (YOUR NAME,PERIOD, DATE)

Evidence of Continental Drift  Pangaea – (pan= all; gaea= Earth) A large landmass that the continents A large landmass that the continents fit together to form fit together to form  Evidence (Page 2) Plates fit together Like a Puzzle Plates fit together Like a Puzzle Matching rocks on different continents Matching rocks on different continents Land animals on different continents Land animals on different continents Glacial marks in now tropical areas Glacial marks in now tropical areas Tropical plants in Antarctica Tropical plants in Antarctica

YOUR PROJECT  Write a letter from Alfred Wegener’s perspective.  Your letter should use evidence (see board) and should try to convince the scientific community that his hypothesis is in fact accurate  Include at least 2 pictures on each page of your journal

The continents fit together

Fossils of same species found on different continents.

Tectonic plates

Forming Crust  Mid-Ocean ridge- Underwater mountain range winds through all oceans  Seafloor spreading occurs at the ridge This is where molten rock reaches the surface, cools, and forms new crust This is where molten rock reaches the surface, cools, and forms new crust As this new crust forms the magnetic minerals in the crust align in relation to Earth’s current magnetic field As this new crust forms the magnetic minerals in the crust align in relation to Earth’s current magnetic field Scientists can look at the sea floor to get a history of Earth’s magnetic reversals (we will talk about how this works in a minute) Scientists can look at the sea floor to get a history of Earth’s magnetic reversals (we will talk about how this works in a minute)

Seafloor Spreading  Harry Hess ( )- left his depth recorder on while traveling as sea in the Navy. He noticed mountain ridges at the center of the ocean basins and deep, narrow trenches at the edges Published his idea of sea floor spreading which suggested that new ocean crust is formed at ridges, split apart and moves away from ridges Published his idea of sea floor spreading which suggested that new ocean crust is formed at ridges, split apart and moves away from ridges

Seafloor Spreading  It was confirmed that sea floor spreading does occur at mid-ocean ridge  Crust is also being destroyed at ocean trenches (we will talk about this in a minute) This is called subduction This is called subduction

New crust is made at the mid-ocean ridge

Magnetic Field Reversals  Fredrick Vine and Drummond Matthews (1963) Combined the pattern of magnetic sea floor stripes with sea floor spreading. Can see fluctuations in rock from normal polarity to reverse polarity. Combined the pattern of magnetic sea floor stripes with sea floor spreading. Can see fluctuations in rock from normal polarity to reverse polarity.

Magnetic field reversals- This is the piece of Evidence that made The continental drift Theory widely accepted Among scientists. As the sea floor spreads (at mid-atlantic ridge) the Magnetism of the rocks Formed reverses. These Magnetic shifts can be Observed in crust.

Being able to identify these magnetic pole reversals in the rock Confirmed the theory of continental drift.

Plate Boundaries- 3 types  Divergent Boundaries  Convergent Boundaries Ocean to Ocean Ocean to Ocean Ocean to Continental Ocean to Continental Continental to Continental Continental to Continental  Transform Boundaries

Divergent boundaries  Plates are moving apart Ocean crust – Ocean crust Ocean crust – Ocean crust Sea floor createdSea floor created Mid-Atlantic RidgeMid-Atlantic Ridge Continental crust – Continental crust Continental crust – Continental crust Continental riftingContinental rifting Sea floor createdSea floor created Continents are splitting apartContinents are splitting apart Red Sea, Gulf of California

This is how the Mid-Atlantic ridge started!

Convergent Boundaries  Plates are moving together Ocean –Continent Ocean –Continent Old sea floor destroyedOld sea floor destroyed Subduction zone (continental arcs)Subduction zone (continental arcs) Subduction- A process in which one plate descends below another (volcanoes) Subduction- A process in which one plate descends below another (volcanoes) Ocean –Ocean Ocean –Ocean Old sea floor destroyedOld sea floor destroyed Subduction zone (island arcs) (volcanoes)Subduction zone (island arcs) (volcanoes) Continent –Continent Continent –Continent Collision ZoneCollision Zone Mountains formMountains form Why does subduction occur? Hint: composition of plates

Continental/Oceanic Examples of Convergent Plate boundaries

Transform Boundaries  Plates are moving past each other Oceanic Oceanic Continental Continental Both of these neither create nor form sea floorBoth of these neither create nor form sea floor Causes EarthquakesCauses Earthquakes

What do we know about all of the locations of these active volcanoes?