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Plate TectonicsNotes

Geology – the study of the Earth and its processes

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The Earth’s Layers

Scientists study seismic (earthquake) waves and volcanic explosions to learn about the Earth’s interior.

Crust

Mantle

Outer Core

Inner Core

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Crust– outermost layer– thinnest layer– the layer we live on– divided into pieces, called tectonic plates– two types: continental and oceanic crust

Mantle– thickest layer– “flows” and allows the tectonic plates to

move on top– primarily magma

The Earth’s Layers cont…

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Outer Core– liquid

Inner Core– solid– dense, high pressure layer at the center

of the earth

The Earth’s Layers cont…

Core is made primarily of iron and

some nickel

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Alfred Wegener

1912 - proposed that all the continents were once joined as a single landmass

–he called this “supercontinent” Pangaea

–stated the continents have separated and collided as they have moved over millions of years

–called his theory “continental drift”

Continental DriftSlide does not

need to be copied

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Wegener’s 5 major pieces of Evidence:

1. Continents (esp. South America &

Africa) seem to fit together like pieces of a puzzle

2. Matching fossils occur on east coast of S. America & west coast of Africa

3. Matching folded mountain belts on coasts of S. America & Africa

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Evidence cont…

4. Evidence of ancient climates show landmasses were once located elsewhere- Ex: glaciers in Africa !

5. Data for latitudes & longitudes of locations is changing

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Wegener is debated

Other scientists argued that the continents could not just plow through the oceans

Later evidence revealed Wegener was correct – he just didn’t have the technology to prove how the continents had moved

Modern Theory = Plate Tectonics

The crust is made up of about a dozen major, moving plates and several smaller plates

Plates can contain:– land = continental crust– ocean = oceanic crust– Both !

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Modern Evidence from the OceansScientists mapping the ocean floor found:

Underwater mountain chains

Ridges where the sea floor was actually spreading at sites called ridges Some oceans were growing wider from the

middle Fossils and other materials are moving

apart on either side of ridges Newer, younger crust was being created by

magma at the ridges11

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Magnetic measurements of the crust Polarity (magnetic north vs. south)

changes every so many thousand years Magnetic rocks on the ocean floor show

reversals Rocks are in equal bands on either side

of the mid-ocean ridges

Modern Evidence cont…

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What Moves the Plates? Convection currents are created as

heated rock rises to the surface, cools, and sinks again.

These currents carry the plates as if they are on a

conveyor belt in a process called “slab pull.”

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Two different plates meet at a boundary.

There are 3 types of plate boundaries:

1. Convergent = where plates collide

2. Divergent = where plates are move apart

3. Transform = where plates move up against one another

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Convergent Boundaries:

When these 2 pieces of crust collide, they buckle and push upwards, forming mountains = uplift occurs

Ex: Himalayas & Mount Everest

Type 1: continental / continental

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continental crust

to draw & label:

Uplifted mountains

continental crust

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Oceanic is denser, so it sinks at the trench between the plates = called the subduction zone

The melting of the oceanic crust forms new magma which is less dense than surrounding rock, so it rises, forming volcanoes

Ex: Mt. St. Helens

Type 2: continental / oceanic

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continentalcrust

to draw & label:

oceaniccrust

trench

melting

volcanoes

the mantle

magma

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The denser plate is subducted / sinks.

The melting of the crust forms new magma which will rise above the denser rock – as it cools,

it may pile up to form land

Ex: Hawaiian Islands & Japan

Type 3: oceanic / oceanic

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to draw & label:

oceaniccrust

trench

melting

land & volcanoes

the mantle

magma

oceaniccrust

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Hot Spots In several places on earth, hot magma

moves upwards through the crust

As a plate moves over this source of magma, volcanoes form at the hot spot.

As the plate continues to move, a chain of volcanoes of differing ages forms

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Divergent Boundaries: The area where 2 plates are

moving away from one another is called a rift zone.

Magma will rise up to fill the gap, cool, and harden to form new crust.

When this happens in the ocean, the process is called sea-floor spreading.

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Ex: Mid-ocean ridge in the Atlantic – note: the youngest crust will be found in these areas

Ex: Great Rift Valley in Africa – note: the inland sea that resulted

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to draw & label:

oceaniccrust

the mantlemagma

oceaniccrust

mid-ocean ridgesea-floor spreading

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to draw & label:

continentalcrust

subsidence

continentalcrust

rift zone

step 1

step 2

inland sea

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Transform Boundaries:

Two plates may grind and jerk as they slide past one another.

The boundary where they meet is called a fault line.

The stressful movement often results in earthquakes.

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Ex: San Andreas Fault

Transform Boundary

to draw & label:

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continent

ocean

AB

C

D

1. Feature _____ is an ocean trench.

2. Feature _____ is undergoing subduction.

3. Feature _____ is part of the continental crust.

4. Feature _____ is part of the mantle.

5. Feature _____ is part of the oceanic crust.

For discussion:

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The “Ring of Fire”- A large number of the world’s

volcanoes and earthquakes occur around the edges of the Pacific plate

For discussion: