Earth ShapingEarth ShapingChapter 16Chapter 16

Earth Shaping TheoryEarth Shaping Theory It was a gradual change over time. In early 1900’s Alfred Wegener proposed the

theory of continental drift. Scientist DID NOT support his theory

because at that time he could not explain his theory.

Current Continental Drift Current Continental Drift TheoryTheory

The earth is constantly changing. In addition to the effects of weathering and erosion, there are much larger scale changes occurring due to the movement of large plates in the lithosphere.

HOW DO WE KNOW HOW DO WE KNOW THIS?THIS?

Wegener developed his idea based upon 4 different types of evidence:

1. Fit of the Continents

2. Fossil Evidence

3. Rock Type and Structural Similarities

4. Paleoclimatic Evidence

Earth’s Earth’s LayersLayers

Inner Core - made of ironInner Core - made of iron

Outer Core–molten(liquid)Outer Core–molten(liquid)

Mantle – most of Earth’s massMantle – most of Earth’s mass

Crust- rocky and brittle, can fractureCrust- rocky and brittle, can fracture

How do we know?How do we know?Measuring seismic wavesMeasuring seismic waves

The speed of the wave determines the type The speed of the wave determines the type of rock it is traveling throughof rock it is traveling through

Do waves travel faster in solids or liquids? Do waves travel faster in solids or liquids?

TWO TYPES OF CRUSTS:TWO TYPES OF CRUSTS:

Oceanic – thin, dense rockOceanic – thin, dense rock

Continental- thick, low densityContinental- thick, low density

LITHOSPHERE-Outer LITHOSPHERE-Outer part of the crust; part of the crust; divided into divided into tectonic platestectonic plates

ASTHENOSPHERE- ASTHENOSPHERE- the tectonic the tectonic plates are on the plates are on the asthenosphereasthenosphere

Plate MovementPlate MovementContinental Drift – the movement of the Continental Drift – the movement of the

tectonic platestectonic plates

Theory -Theory -that continents drift apartthat continents drift apart

*Proposed by Alfred Wegner *Proposed by Alfred Wegner *Fossil evidence*Fossil evidence

Sea Floor SpreadingSea Floor SpreadingMagma Rises in mid –ocean ridges or cracks called Magma Rises in mid –ocean ridges or cracks called

fissuresfissures

1. Forms new crust1. Forms new crust

2. Moves horizontally2. Moves horizontally

3. Older crust moves further out 3. Older crust moves further out

Magnetic ReversalsMagnetic Reversals Earth’s north and south Earth’s north and south

magnetic poles change magnetic poles change placesplaces

Can be seen in the Can be seen in the oceanic crustoceanic crust

Magnetic minerals align Magnetic minerals align with magnetic fieldwith magnetic field

SupercontinentSupercontinent

Pangea – all of the Pangea – all of the continents were continents were joined togetherjoined together

Gradually drifted Gradually drifted apart over time.apart over time.

Plate Tectonic TheoryPlate Tectonic Theory3 Possible Forces3 Possible Forces

Ridge PushRidge PushConvectionConvectionSlab pull/SubductionSlab pull/Subduction

Ridge PushRidge Push – –

gravity causes gravity causes oceanic crust oceanic crust (lithosphere) to (lithosphere) to sink, subsidencesink, subsidence

Convection Slab PullConvection Slab Pull Hot rock rises while Hot rock rises while

cool rock sinks cool rock sinks Causes the Causes the

lithosphere to move lithosphere to move sidewayssideways

Subduction Zone- when Subduction Zone- when oceanic lithosphere (crust) oceanic lithosphere (crust) is more dense causing the is more dense causing the edge to sink and pull the edge to sink and pull the rest of the plate with itrest of the plate with it

African, North American, South American, Eurasian, Australian, African, North American, South American, Eurasian, Australian, Antarctic, and Pacific plates. Several minor plates also exist, Antarctic, and Pacific plates. Several minor plates also exist, including the Arabian, Nazca, and Philippines plates. including the Arabian, Nazca, and Philippines plates.

7 Tectonic Plates

MOVEMENT: MOVEMENT:

*Different *Different directions & directions & speedsspeeds

*2-10cm per year *2-10cm per year (the speed your (the speed your fingernails grow)fingernails grow)

Plate BoundriesPlate Boundries Convergent – come togetherConvergent – come together Divergent – pull apartDivergent – pull apart Transform – slide past each otherTransform – slide past each other

ReviewReview

Magma moves in _______Magma moves in _______

currents due to change in currents due to change in temperatures.temperatures.

convection

When rock layers come together it is a When rock layers come together it is a ________________

boundary.boundary.

When they pull apart it is a When they pull apart it is a

_________ boundary._________ boundary.

boundary.boundary.

convergent

divergent

Tectonic plates are large pieces of Tectonic plates are large pieces of ______________________

A rock is made of 2 or more A rock is made of 2 or more ________________________

lithosphere

minerals

1

2

3

What rock type is at 1?What rock type is at 2?What rock type is at 3?