Plate TectonicsPlate Tectonics

Plate Tectonics and the Ocean Plate Tectonics and the Ocean FloorFloor

Plate tectonicsPlate tectonics – Theory that the – Theory that the outermost portion of the Earth is outermost portion of the Earth is composed of plates that move on a liquid composed of plates that move on a liquid molten layer (similar to icebergs floating molten layer (similar to icebergs floating on water)on water)

Alfred WegenerAlfred Wegener a German meteorologist a German meteorologist developed the theory of continental drift in developed the theory of continental drift in 19121912

Continental drift-Continental drift- Continents slowly drift Continents slowly drift across the globeacross the globe

Evidence of Continental Evidence of Continental DriftDrift

PangaeaPangaea – (pan= all; gaea= Earth) – (pan= all; gaea= Earth)

A large landmass that the continents A large landmass that the continents

fit together to formfit together to form EvidenceEvidence

Matching rocks on different continentsMatching rocks on different continents• Similar rocks form Appalachian mountains match rocks in Similar rocks form Appalachian mountains match rocks in

British IslesBritish Isles Distribution of organismsDistribution of organisms

• Finding fossils of the same species on different continentsFinding fossils of the same species on different continents Glacial Activity in now tropical areasGlacial Activity in now tropical areas

The continents fit together

Fossils of same species found on different continents.

More on Continental DriftMore on Continental Drift

As the seafloor spreads the As the seafloor spreads the lithosphere lithosphere (continental and oceanic crust) (continental and oceanic crust) moves moves in sections on a viscous liquid layer- in sections on a viscous liquid layer- asthenosphereasthenosphere

On average these tectonic plates move 1-On average these tectonic plates move 1-5 inches/year5 inches/year

More on More on Continental driftContinental drift If new crust is being formed all the time why isn’t If new crust is being formed all the time why isn’t

the earth covered in crust?the earth covered in crust? Because as new crust is formed old crust is Because as new crust is formed old crust is

destroyeddestroyed Let’s start by looking at the 2 types of crustLet’s start by looking at the 2 types of crust

Both types of crust make up the outer layer of earth, Both types of crust make up the outer layer of earth, called the called the lithospherelithosphere

Continental CrustContinental Crust• GraniteGranite• Lower density than continentalLower density than continental

Oceanic CrustOceanic Crust• Igneous rock + basaltIgneous rock + basalt• Higher density than continentalHigher density than continental

Continental driftContinental drift

The crust sits on top of a The crust sits on top of a viscousviscous layer – layer – the the asthenophereasthenophere A A ViscousViscous substance is a thick liquid substance is a thick liquid

• What are some examples of a viscous substance What are some examples of a viscous substance that you are familiar with?that you are familiar with?

The The asthenosphereasthenosphere is part of the mantle is part of the mantle called the called the upper mantleupper mantle

ConvectionConvection

Convection is the heat transfer in a gas or Convection is the heat transfer in a gas or liquid by the circulation of currents from liquid by the circulation of currents from one region to anotherone region to another

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

ConvectionConvection

Convection causes movement in the liquid Convection causes movement in the liquid mantle layer which the crust sits uponmantle layer which the crust sits upon

As a result the crust slowly moves on this As a result the crust slowly moves on this layerlayer Kind of like an iceberg floating on waterKind of like an iceberg floating on water

As this occurs the tectonic plates move As this occurs the tectonic plates move slowly over the asthenosphereslowly over the asthenosphere

Tectonic platesTectonic plates

Forming CrustForming Crust

Mid-Ocean ridgeMid-Ocean ridge- Underwater mountain range - Underwater mountain range winds through all oceanswinds through all oceans

Seafloor spreadingSeafloor spreading occurs at the ridge occurs at the ridge This is where molten rock reaches the surface, cools, This is where molten rock reaches the surface, cools,

and forms new crustand forms new crust As this new crust forms the magnetic minerals in the As this new crust forms the magnetic minerals in the

crust align in relation to Earth’s current magnetic fieldcrust align in relation to Earth’s current magnetic field Scientists can look at the sea floor to get a history of Scientists can look at the sea floor to get a history of

Earth’s magnetic reversals (we will talk about how this Earth’s magnetic reversals (we will talk about how this works in a minute)works in a minute)

Seafloor SpreadingSeafloor Spreading

Harry Hess (1906-1969)-Harry Hess (1906-1969)- left his depth left his depth recorder on while traveling as sea in the recorder on while traveling as sea in the Navy. He noticed mountain ridges at the Navy. He noticed mountain ridges at the center of the ocean basins and deep, center of the ocean basins and deep, narrow trenches at the edgesnarrow trenches at the edges Published his idea of sea floor spreading Published his idea of sea floor spreading

which suggested that new ocean crust is which suggested that new ocean crust is formed at ridges, split apart and moves away formed at ridges, split apart and moves away from ridgesfrom ridges

Seafloor SpreadingSeafloor Spreading

It was confirmed that sea floor spreading It was confirmed that sea floor spreading does occur at mid-ocean ridgedoes occur at mid-ocean ridge

Crust is also being destroyed at ocean Crust is also being destroyed at ocean trenches (we will talk about this in a trenches (we will talk about this in a minute)minute) This is called This is called subductionsubduction

New crust is made at the mid-ocean ridge

Magnetic Field ReversalsMagnetic Field Reversals

Fredrick Vine and Drummond Matthews Fredrick Vine and Drummond Matthews (1963)(1963) Combined the pattern of magnetic sea floor Combined the pattern of magnetic sea floor

stripes with sea floor spreading. Can see stripes with sea floor spreading. Can see fluctuations in rock from normal polarity to fluctuations in rock from normal polarity to reverse polarity.reverse polarity.

Magnetic field reversals-

This is the piece of Evidence that made The continental drift Theory widely acceptedAmong scientists.

As the sea floor spreads(at mid-atlantic ridge) the Magnetism of the rocks Formed reverses. TheseMagnetic 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 typesPlate Boundaries- 3 types

Divergent BoundariesDivergent Boundaries Convergent BoundariesConvergent Boundaries

Ocean to OceanOcean to Ocean Ocean to Continental Ocean to Continental Continental to ContinentalContinental to Continental

Transform BoundariesTransform Boundaries

Divergent boundariesDivergent boundaries

Plates are moving apartPlates are moving apart Ocean crust – Ocean crustOcean crust – Ocean crust

• Sea floor createdSea floor created• Mid-Atlantic RidgeMid-Atlantic Ridge

Continental crust – Continental crustContinental crust – Continental crust• Continental riftingContinental rifting• Sea floor createdSea floor created• Continents are splitting apartContinents are splitting apart

Red Sea, Gulf of CaliforniaRed Sea, Gulf of California

This is how the Mid-Atlantic ridge started!

Convergent BoundariesConvergent Boundaries Plates are moving togetherPlates are moving together

Ocean –ContinentOcean –Continent• Old sea floor destroyedOld sea floor destroyed• Subduction zone (Subduction zone (continental arcscontinental arcs))

Subduction- A process in which one plate descends Subduction- A process in which one plate descends

below another below another (volcanoes)(volcanoes) Ocean –OceanOcean –Ocean

• Old sea floor destroyedOld sea floor destroyed

• Subduction zone (Subduction zone (island arcsisland arcs) ) (volcanoes)(volcanoes) Continent –ContinentContinent –Continent

• Collision ZoneCollision Zone• Mountains formMountains form

Why does subduction occur? Hint: composition of plates

Continental/Oceanic

Examples of Convergent Plate Examples of Convergent Plate boundariesboundaries

Transform BoundariesTransform Boundaries

Plates are moving past each otherPlates are moving past each other OceanicOceanic ContinentalContinental

• 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?