Transcript Plate Tectonics

Plate Tectonics
What Did
The Earth
Look Like
In The
Past?
CONTINENTAL DRIFT THEORY
• Alfred Wegener - 1912 - developed theory of a large land mass called Pangaea (means
all land). The ocean was called Panthalassa. He thought Pangaea broke apart and
floated on the ocean floor due to earth’s rotation.
• Evidence of proof: fossils of plants & animals, rocks, glacial clues, matching climate
and continents fitting together like a puzzle.
• Theory was ignored because there was no explanation of how, when, or why these
changes took place.
Evidence of Continental Drift
GLOSSOPTERIS - G
Fossil plant /Similar climate
LYSTROSAURUS - L
A small reptile
R
ROCK CLUE - R
Rock structures are
similar types & ages
C/W
R
R
GL
G
GL
R
GLACIERS - GL
Glacial deposits &
Rock surfaces scoured
& polished by glaciers
CLIMATE - C
Warm weather plants
GL
G
L
G
R
L
M
M
L
G
G
GL
MESOSAURUS - M
Freshwater/Land reptile
Principle of Uniformitariantism - states that the processes we see
changing Earth’s surface today are the same as those that changed it in the past.
Principle of Superposition - states that layers of sedimentary rock near
the surface are younger than layers of rock deeper down, unless something
Has disturbed the layers.
Unconformity - is a place where rock layers are missing.
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In 1968, scientists aboard the research ship Glomar Challenger drilled into the seafloor
for rock samples. They discovered that the youngest rocks were located on the
mid-ocean ridge in the Atlantic Ocean. The rocks became older as they moved farther
away from the ridge.
PLATE TECTONICS
This gave evidence to the theory of seafloor spreading that was suggested by a
Princeton University scientist, Harry Hess. Hess was on a Navy vessel in WW II,
mapping the ocean floor with a fathometer - a type of sonar that used echo sounding to
help ships know where the bottom of the ocean floor was. He proposed that hot, less
dense material below the crust rises toward the surface at the mid ocean ridges,
flowing sideways, carrying the seafloor away from the ridge in both directions.
1.
SEAFLOOR
SPREADING
3.
Divergent plates spread apart
from each other, creating new
crust. Hot, molten magma
rises to the surface of the ocean
floor, pushing the floor outward.
5. On the Mid- Atlantic Ridge, the
North American plate is moving
away from the Eurasian and the
African Plates. This process is
making the Atlantic Ocean larger.
4.
The Great Rift Valley in eastern
Africa is becoming a divergent
plate boundary. Iceland is also.
6.
When new seafloor is created
by this plate movement, the
magma cools quickly, forming
a crust made of basalt rock.
This creates a very heavy,
dense crust, even though it
is only 3 miles thick.
Names of Plates
The Earth’s crust appears to be broken into pieces like a puzzle, which are
called plates. These rigid plates are being moved by the convection currents
in the hot, molten mantle. The plates spread apart, collide or slide past each
other, causing earthquakes, volcanoes, mountains and ridges. The plates can
move 2 to 15 centimeters each year.
Plates Move Away From Each Other
This is called Divergence – these are constructive
boundaries since they produce new land
Africa and Arabia
Mid-Atlantic Ridge
North America
and Eurasia
Divergence – Moving Apart
Rift Valley –
if the land is
above water
Sea Floor
Spreading –
when the land is
below water
Plates Move Toward Each Other
This is called Convergence – these are destructive
boundaries since they deform the plates
19.
15.
14.
Subduction
20.
Convergent
21.
Folded Mountains
Continent/Continent
Ocean/Continent
13.
Convergent
17.
16.
18. Andes Mountains
11.
8.
Ocean/Ocean
9.
Subduction
10.
12.
Convergence – Moving Together
Trenches
Mountains
22.
Structural
Mountains
Volcanic
Mountains
7. A convergent boundary
is created when two plates
collide into each other. When
this occurs, mountains and/or
volcanoes are created and
earthquakes can happen. When
the heavier oceanic floor collides
into the lighter continental crust,
the continental crust is pushed
over the oceanic crust. The
oceanic crust “dives” under the
continental crust creating a
subduction zone. Land is lost
in this area. The Pacific Ocean is
getting smaller because of this
process.
Rock parts
pulled
Apart from
faults
Rock layers folded
Or
compressed
Plates sink and
Melting occurs
Lava piles up
From magma
Forces in Earth
Push on crust
Sierra &
Teton
Range
Appalachians
Hawaiian
Islands
Rocky
&
Adirondack
Active Movements - Faults
One day – Los
Angeles and San
Francisco will be
next to each
other
26.
23. Transform
24.
25.
Shearing
TRANSFORM FAULT
This type of boundary occurs where two plates slide past one
another. They move in opposite directions or in the same
direction at different rates. When one plate slips past another
suddenly, earthquakes occur.
FAULTS are fractures or break in earth’s crust - movement has taken place - rock
strata layers do not match - create mountains- Niagara Falls.
Blocks are pulled apart
overlying block moves
down the fault plane.
A spreading zone.
Sierra Nevada's
Hanging Wall
Foot Wall
Squeezing or compressing
Blocks are pushed together
Moves up the fault plane.
Himalayas Mts. - India
Foot Wall
Transform - strike slip fault - a lateral fault
Slide past each other.
San Andreas, CA.
Hanging Wall
CONVERGENT
CONVERGENT
LAND
OCEAN
DIVERGENT
Earthquakes, Volcanoes & Mountains
Earthquakes
Earthquakes & Volcanoes
Divergent
Convergent
Sea floor
spreading
Collision of
Ocean-ocean
Subduction
Convergent
Collision of
Continental/
oceanic
subduction
Convergent
Collision of
Continental/
continental
Transform
Shearing
Mid ocean
ridge
Rift Valley
Island arc
Trench
Mid-Atlantic
Ridge
Iceland
Convergent
Ocean-ocean
Trench
Volcanic
mountains
Folded
mountains
Transform
fault
Andes
Mountains
Himalaya
Mountains
San Andreas
fault
Types of Boundary –
convergent, divergent, transform
Choices of Motion at Boundary –
collision of continental/continental
Collision of oceanic/oceanic
Collision of continental/oceanic
Ocean floor spreading
Shearing
Subduction
Land Features Formed Island arc
Folded mountains
Mid-ocean ridge
Rift valley
Transform fault
Trench
Volcanic Mountains
Actual Examples –
Andes Mountains
Aleutian Islands
Himalaya Mountains
Iceland
Mid-Atlantic Ridge
San Andreas