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Earth Science
Notes
Geology – the study of the
Earth and its processes
1
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
2
The Earth’s Layers cont…


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
3
The Earth’s Layers cont…

Outer Core
– liquid
 Inner
Core is made
primarily of iron and
some nickel
Core
– solid
– dense, high pressure layer at the center
of the earth
4
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”
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Continental Drift
Slide does not
need to be
copied
6
Wegener’s 5 major pieces of Evidence:
1.
2.
3.
Continents (esp. South America &
Africa) seem to fit together
like pieces of a puzzle
Matching fossils occur on
east coast of S. America &
west coast of Africa
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
9
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 !
10
Modern Evidence from the Oceans
Scientists 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 ridges
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Modern Evidence cont…
 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
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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 move
apart
3. Transform = where plates move
up against one another
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Convergent Boundaries:
Type 1: continental / continental


When these 2
pieces of crust
collide, they
buckle and push
upwards, forming
mountains =
uplift occurs
Ex: Himalayas &
Mount Everest
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to draw & label:
Uplifted
mountains
continental
crust
continental
crust
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Type 2: continental / oceanic


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

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to draw & label:
volcanoes
oceanic
crust
continental
crust
magma
the mantle
melting
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Type 3: oceanic / oceanic



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
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to draw & label:
land & volcanoes
oceanic
crust
oceanic
crust
magma
the mantle
melting
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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
23 23
to draw & label:
oceanic
crust
the mantle
mid-ocean ridge
sea-floor spreading
oceanic
crust
magma
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to draw & label:
continental
crust
continental
crust
subsidence
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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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.
continent
C
ocean
B
A
D
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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
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