Download 8_Plate_Tectonics_n_Layers_of_the_Earth

Alfred Wagner
• – proposed that in the
distant past, the
Earth’s continents
were all joined as a
single landmass.
• What was the name
of his hypothesis?
• Continental Drift
Evidence of Wagner’s Theory
1.
Landforms Fit like a Puzzle
*Pangaea – when Wegener placed all the
continents together like a puzzle, it
formed a large landmass which he called
Pangae
2.
Matching of Fossil & Ancient
Rock
*Glacial Till Deposits – glaciers from
South Africa & North Australia
3.
Climate Evidence in Rock
Layers:
•South America, Africa, India, Antarctica,
and Australia show remarkable
similarities
•Same three layers in the same order in
areas TODAY are separated by oceans.
Wegener named Pangea:
-the Southern portion Gondwana
-the Northern portion Laurasia
“Puzzle” of Continents Over
Time
Why was Wagner’s theory not
accepted?
• Wagner could not explain the forces that caused the
continents to move. (mechanism of movement)
• Most Scientists believed that Earth was solid and immovable.
What two Scientists had evidence to
support Wagner’s theory?
-Arthur Holmes
• Thermal convection in mantle
“move” continents
–Harry Hess 
• Using radar (new technology)
he discovered the seafloor has
trenches and mid-ocean ridges
• Proposed Sea-floor Spreading
Theory
– Led into Plate Tectonics…
What is Sea-floor
Spreading?
So…as Seismic Technology Advanced:
• Wagner’s Theory was Proven
• Layers of the Earth were
identified:
– Lithosphere, Asthenosphere,
Mantle, Inner/Outer Core, Crust
• Layering based on:
– Density
– Chemical Composition
– Mechanical Behavior of Material
The Outer & Inner Core
The Outer Core
The Inner Core
*liquid layer of very hot metals
*Solid layer due to extreme
pressure
*temperature greater than
6,000 C
*Main Minerals/Metals:
*Mostly Iron, some nickel
The Core
• The way in which P waves are refracted within the
earth’s core suggests that the core has two parts,
a liquid outer core and a solid inner core
• WHY??
The Mantle
-Largest layer of the Earth
*29,000 km thick
*67% of Earth’s mass
-Beneath the crust
-Main Elements:
*Oxygen, Silicon, Magnesium,
Iron, Aluminum
-Made of Magma
*very hot dense rock that flows
-The movement of the
upper mantle
(asthenosphere) is the
reason that the crustal
plates of the Earth move.
Studying the Mantle
• Scientists cannot observe the mantle directly
• SO how do they study the mantle??
• Using Observations made from Earth’s surface:
• Data from Earthquakes and Volcanic Eruptions
• S Waves & P Waves
• Studying Magma
• Studying the Ocean Floor
• Lava – Molten rock(magma) that reaches Earth’s surface
The Crust
• Made of Light, brittle rocks
• Main Elements:
– Oxygen
– Silicon
– Aluminum
• Very thin in comparison to
the other three layers
– like the skin of an apple. It is.
• Only 1% Earth’s mass.
• Two types of crust:
– Continental
– Oceanic
The Crust: Two Main Kinds
1. Continental crust -- under the continents
-lighter, older, thicker, mostly granite.
-About 25 miles (32 kilometers) thick
2. Oceanic crust -- under the oceans
-twice as much iron, magnesium, and calcium as continental
-mostly basalt.-much denser than the granite
-3-5 miles (8 kilometers) thick under the oceans
**the less dense continents ride on the more denser oceanic plates.
What are differences between
oceanic crust and continental crust?
1. The continental crust is composed
of granite while the oceanic crust is
composed of basalt.
2. The density of the continental crust
is less than the oceanic crust, thus it
floats higher on the mantle.
Tectonic Plates
Lithosphere-
Asthenosphere-
*Crust and rigid upper part of
the mantle
*Similar to giant jigsaw puzzle
*Each “piece” is Tectonic Plate
– large section of
lithosphere that is in
slow, constant motion
* soft, semi-rigid layer within
the upper mantle that
flows like a thick liquid
*Tectonic plates "float” or
move on the asthenosphere
Convection Currents
* caused by very hot MAGMA
at the deepest part of the
mantle rising, then cooling
and sinking again --repeating
this cycle over and over
*The middle mantle "flows"
because of convection
currents.
*This movement beneath the
plates causes the plates to
move
Convection Currents
The next time you heat anything
like soup or water in a pan you can
watch the convection currents
move in the liquid. When the
convection currents flow in the
asthenosphere they also move
the crust. The crust gets a free ride
with these currents, like the cork in
this illustration.
Safety Caution: Don’t get your
face too close to the boiling water!
*Use your knowledge…how do
you think a convection oven
cooks food?
Plate Boundaries Around the World
Review:
The Layers of the Earth
The Earth is composed of how many
layers?
1. crust
-layer that you live on
--most widely studied and
understood.
2. mantle
- much hotter
-has the ability to flow.
3. outer core and inner core -- -hottest layer
-high pressure
*In which layer is most of the mass of
the Earth located?
The Mantle
*The mantle increases in temperature
depending on how close it is to _______.
The Core
The rocks in the ____ mantle are brittle
and break while the rocks in the
_____mantle are soft and flow instead of
break.
Upper; Lower
The core is thought to be
composed of ___ & ____.
*nickel and iron
Which core layer is liquid?
*Outer
Which core layer is solid?
*Inner
What causes the Inner core to be
solid?
*Tremendous pressure, produced by the
weight of the overlying rocks
Review Time:
• What is the
• What is the
Lithosphere?
Asthosphere?
–The crust and part
–Softer layer of the
of the upper
mantle
–100 km thick
• Why does it float?
–Less dense than
the material below
it so it “floats”
upper mantle that
flows
• What process
causes the
asthenosphere to
flow?
–Convection Current