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Plate Tectonic Notes. May 4, 2012. I. Earth’s Interior. A. Layers of the Earth 1. Crust : thin and solid outermost layer of Earth above the mantle

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i earth s interior
I. Earth’s Interior

A. Layers of the Earth

1. Crust: thin and solidoutermost layer of Earth above

the mantle

a. Continental crust is lessdense and thicker(20-40km) (12-25 mi) than oceanic crust, which is more dense and thinner(5-8km) (3.1-4.9 mi)

lithosphere asthenosphere
Lithosphere & Asthenosphere
  • Lithosphere(60 mi thick) is made up of the crust and the upper portion of the mantle
  • Asthenosphere-hot, plastic portion of the mantle that can flow

-soft rock in the


circulates by

convection currents

& this results in slow

movement of plates


2. Mantle: layer of rock between the Earth’s crust and core

a. Denser than the crust

b. Outermost part is solid and rigid, but as you move closer to the core, the mantle becomes soft and easily deformed (like plastic portion of mantle)

1. Called the asthenosphere

  • *Also, very hot
  • (1200℃ or 2280℉)

3. OuterCore: Liquid metal outer edge of core

a. Composed mainly of iron and nickel

4. InnerCore: Solid metal inner core

a. Composed mainly of iron and nickel

*Temps are

thought to be

above 10,800℉

*Earth’s center

has radioactive

isotopes that do

fission & release

a ton of heat



B. As you travel from crust into the core, the temperature increases

1. Temperatures from 375oC at the crust to over 6000oC (10,800 ℉)in the inner core

C. Thermal Energy Transfer

1. Material moves with the Earth as a result of conduction (transfer thermal energy from individualatom to

individualatom) and

convection currents

(hot material rises &

cool material sinks

back to the core)


D. Evidence for Characteristics of Layers

1. P-waves and S-waves (see below)

*P Waves travel through liquids & solids but S Waves cannot travel through liquids

ii continental drift
II. Continental Drift

A. Theory that Earth’s surface is made of large movableplates

1. Alfred Wegener was a German scientist who first proposed the idea that the continents of the Earth were once one large supercontinent

a. Called this supercontinent Pangaea

in 1910 alfred wegener begins to wonder
In 1910 Alfred Wegener begins to wonder.

He thought that:

  • All the continents were stuck together at one time (300 million years ago?).
  • Continental drift = slow movement of continents over Earth’s surface.
supercontinent called pangea
Supercontinent called PANGEA

Pangea means all lands

wegener s evidence

Wegener’s summary was based on various careful observations:

#1 - All of the coastlines of the continents seemed to fit together like puzzle pieces.

Wegener’s Evidence

wegener s evidence1

#2 - Fossil evidence:

Identical fossils found on different continents

Wegener’s Evidence

wegener s evidence2

#3 - Glacial Evidence:

  • Large ice masses carve grooves in the rocks over which they flow.
  • Such masses tend to flow outward (generally downhill) from a central locality.

Wegener’s Evidence

wegener s evidence3

#4 - Rock Ages:

the framework of rock ages showed strong correlation across the Atlantic, as did mountain ranges of similar age.

Wegener’s Evidence


B. Early evidence for Continental Drift

#5. Migration patterns of animals have not changed since it was supercontinent.


C. Recent evidence for Continental Drift

1. Magneticpolarity bands near mid-ocean ridge [Fig 6, p.703]

a. Alternating magnetic bands, normal versus reversed, on new ocean floor

2. Age of rocks relative to the mid-ocean ridge: the farther away from the mid-ocean ridge, the older the rock

iii plate tectonics
III. Plate Tectonics

A. Lithosphere is made up of the crust and the upper portion of the mantle

1. Divided into 7 major plates and several smaller plates called tectonic plates

2. Continents are embedded into the tectonic plates

3. Plates “float” on the asthenosphere

-hot, plastic portion of the mantle that can


-soft rock in the asthenosphere circulates

by convection currents & this results in

slow movement of plates


B. PlateTectonics: the theory that explains how the outer parts of the Earth change through time

1. Also explains the relationships between continental drift, sea-floor spreading, seismic activity, and volcanic activity

iv plate boundaries
IV. Plate Boundaries

A. Divergent Boundaries: two plates move apart creating a gap between them

1. Causes mid-oceanridges to form

a. Less dense magma rises up

in between the

two separating

plates creating

new oceanfloor

b. Gap between the

two plates is called

a riftvalley

c. Most studied mid-ocean ridge is Mid-Atlantic Ridge


B. Convergent Boundaries: two plates are coming together

1. Forms oceantrenches, volcanoes, &/or mountains

a. Subduction zone: process by which one lithospheric plate moves beneath another as a result of tectonic forces

1. Oceantrench: forms between 2

oceanic plates or oceanic plate and

continental plate

a. Older plate is denser, so it

sinksbelow the other plate

b. Can be extremely deep


2. Volcanoes are formed as the subducting plate is melted and the magma rises to surface on other plate

b. Colliding tectonic plates create mountains

1. Two continental plates collide and the land is pushed upward creating mountains

2. Example: Himalayas

hot spots
Hot Spots
  • A hot spot is an area of persistent volcanic activity that comes from unusually hot areas of the mantle-core boundary.
  • Hawaii, Iceland, and Yellowstone are examples of hot spots.

C. TransformFault Boundaries: two plates sliding past each other

1. Fault: crack in Earth created when rocks on either side of a break move

2. One cause of earthquakes

3. Example: San Andreas Fault (from Mexico to California)

v earthquakes
V. Earthquakes

A. As plates move past each other, pressure builds up and eventually the stress becomes so great it causes the rock to crack

1. Focus: exact point inside Earth when an earthquake originates

2. Epicenter: point on Earth’s surface directly above an earthquake’s focus


B. Energy is transferred by waves

1. Longitudinal waves (P Waves): Move faster through rock, so first waves to reach recording stations

2. Transverse waves (S Waves): Move more slowly, so arrive second to the recording station

3. Surface waves: seismic waves that can only move through solids

earthquake effects tsunami
Earthquake Effects: Tsunami

A tsunami is a giant wave or sequence of waves produced by large water displacements. These are most commonly caused by underwater earthquakes.

Tsunamis can be destructive long distances from their sources.


C. Seismograph: machine that records the movements produced by an earthquake

1. Use seismographs to investigate the Earth’s interior

2. Differences in velocities of the waves indicate the type of material the waves travel through

a. Scientists constructed the model of Earth [Fig. 19, p.712]


D. Richter Scale: a scale that expresses the magnitude of an earthquake

1. Range from 2.0 to 10.0 magnitude

2. No earthquakes have ever been recorded at 9.0 or 10.0