1 Plate Tectonics

Do Now
1. Define interdependent.
2. Identify the 3 types of plate
boundaries found on Earth and
explain their movement using 3
words or less.
Indicate the type of boundary that
results in the following:
**name all types that apply**
a. An earthquake
b. A volcano
c. A mountain
d. A fault
e. A trench
Play at 30 min.
Unit 1
Plate Tectonics
Unit 1 Plate Tectonics
I. Earth’s History
II. Earth’s Interior
III. Plate Boundary
IV. Natural Disasters
V. The Rock Cycle
Earth’s History
A. Geologic Time Scale
Any changes of Earth occurs in geologic
time at a rate that’s undetectable in human
Geologic time scale = hundreds of thousands of
Earth’s history is told by looking at the rock
layers & using radioactive carbon dating to
create a timeline of events when no one was
there to document species or events on
Geologists have determined that Earth’s
age is roughly 4.5 billion years old
B. Human Time Scale
Human time scale= short
Most people think of the next 100 years
This makes it difficult for us to understand
large time spans between geologic events,
plate tectonics, evolution, etc.
Typical human generation = 30 years
Anthropogenic* changes occurred
within last few 1000 years
Anthropogenic = human caused
C. Causes of Seasonal
Changes on Earth:
Tilt & Rotation
Earth’s tilt is approx. 23.5°on its axis
Earth’s rotates every year (365 days) to
make it around the sun
During rotation, Earth’s tilt causes
certain hemispheres to receive more
direct light (summer) & others to receive
less (winter) as well as the intermediate
spring and fall
Earth’s equator receives the
most direct sunlight due to its
circumference as it extends
further out when compared to the
other latitudes such as the poles,
which receive the least angle of
The more direct the angle of
sunlight, the hotter the climates
II. The Earth’s Interior
Earth’s interior is constantly changing
as a result of processes taking place on
and below its surface.
Earth has 3 concentric layers of solid
and/or liquid rock
A. Core
1. Inner core
Solid because very high pressures
Composed of nickel & iron
Gives off heat to the surrounding
mantle layer because of the
radioactive elements which causes
magma to circulate in the mantle
2. Outer core
Semi-solid/liquid because lower
Composed of iron & sulfur
B. Mantle
Composed of
44.8% oxygen
21.5% silicon
22.8% magnesium
There's also iron, aluminum, calcium,
sodium, and potassium
These elements are all bound together
in the form of silicate rocks, all of which
take the form of oxides
Convection in the Mantle
Mantle rocks get close to the
radioactive core & are heated up.
The warmed rocks rise while the
cooler rocks sink away from the crust,
creating slow, vertical currents within
the mantle.
These convection currents cause
earth’s tectonic plates to move in
certain directions based on the direction
of the currents that are next to each
Layers of earth
Continental crust
Oceanic crust Ocean trench
Oceanic crust
Continental crust
cools as it
the outer
Cold dense
falls back
Two plates move
towards each other.
One is subducted back
into the mantle on a
falling convection
Hot outer
the mantle
Fig. 14-3, p. 346
1. Asthenosphere
slowly flowing rock that makes up the
uppermost part of the mantle
Tectonic plates rest on top of this layer
2. Lithosphere
It extends from the upper mantle to the
solid, outermost layer of Earth (crust)
It rests on top of the asthenosphere and
is broken up into pieces called tectonic
Consists of
mostly of rock (“litho-” means rock)
soils, silts, and sediments
It makes up the ocean floor, mountain
ranges, & anything considered “ground”
C. Crust
Solid thin surface of earth
Composed of
basalts and granites
oxygen, 47%
silicon, 27%
aluminum, 8%
iron, 5%
calcium, 4%
magnesium, potassium & sodium, 2%
1. Types of Crust
Oceanic crust – thin (3-6mi), dense;
makes up floors of ocean basins (71%
of total crust)
Continental crust – thick, less dense
(20-30mi); the lithosphere underlying
the continental landmasses
If these two types of crusts come
together, oceanic crust will sink/subduct
beneath the continental crust
Earth’s crust is broken up into large
segments called tectonic plates
They are in constant (VERY SLOW)
They interact with each other in a few
predictable ways at their boundaries
Plate interactions
Changes to Earth’s surface
Internal geologic processes build up
earth’s surface by creating new crust
when magma is exposed at the surface
External geologic processes break
down earth’s surface
Weathering: Physical, Chemical, and
Erosion: Wind, Flowing water,
Human activities, Glaciers
III. Plate Boundary Interactions
A. Divergent plate boundary
(AKA spreading centers)
2 plates move away from one other
As the plates divide, magma rises into the
gap forming rifts (rift volcanoes)
This magma cools to form new crust in the
form of undersea mountains
Forms Rift volcanoes & Ridges
Example: Mid-Atlantic Ridge along the
Atlantic Ocean between the Americas,
Africa & Europe
Not known to cause earthquake activity
because they are not grinding plates
Iceland is splitting
along the MidAtlantic Ridge
between the North
American and
Eurasian Plates.
Over time the mass
of land will break
apart into distinct
land masses & the
surrounding water
will fill the space
between them.
B. Convergent Plate Boundary
2 plates move towards each other & grind
Mostly associated with deep ocean trenches,
subduction volcanoes, & earthquake activity
The plate that is more dense is usually
pushed beneath the less dense plate at a
subduction zone forming trench
The sinking plate pushes into the mantle to
re-melt as magma to form new crust
Could result in a subduction volcano
when plates collide and slide over each
other & magma becomes exposed
a. Converging ocean-ocean
When two oceanic plates converge one is
usually subducted under the other and in the
process a deep oceanic trench is formed.
Oceanic-oceanic plate convergence also
results in the formation of undersea
Over millions of years, the erupted lava &
volcanic debris pile up on the ocean floor
until a submarine volcano rises above sea
level to form an island volcano.
Such volcanoes are typically strung out in chains
called island arcs.
Mariana’s Trench
The Marianas Trench is Earth’s
deepest trench created as the
result of the Pacific Plate
subducting beneath the Philippine
Plate forming a subduction zone
2,550km in length
11km at its deepest
70km wide
b. Converging ocean-continent
When an oceanic plate pushes into and
subducts under a continental plate, the
overriding continental plate is lifted up
and a mountain range is created.
The Ring of Fire
A famous pattern of volcanic & EQ
activity that accounts for almost 75% of
Earth’s volcanoes
Occurs along the continental borders of
the Pacific Ocean where the Pacific
Plate is subducted beneath the
surrounding continental plates
The Mariana’s Trench (Earth’s deepest
crevice) is part of the Ring of Fire
Even though the oceanic plate as a
whole sinks smoothly and continuously
into the subduction trench, the deepest
part of the subducting plate breaks into
smaller pieces.
These smaller pieces become locked in
place for long periods of time before
moving suddenly and generating large
Such earthquakes are often accompanied
by uplift of the land by as much as a few
c. Converging continentalcontinental
When two continents meet head-on,
neither is subducted because the
continental rocks are relatively light and,
like two colliding icebergs, resist
downward motion.
the crust
tends to
buckle and
be pushed
upward or
The collision of India into Asia 50 million
years ago caused the Eurasian Plate to
crumple up and override the Indian
After the collision, the slow continuous
convergence of the two plates over
millions of years pushed up the
Himalayas and the Tibetan Plateau to
their present heights.
Most of this growth occurred during the
past 10 million years.
Convergent & Divergent
3. Transform Fault
Two plates slide/grind from side to
side relative to each other
Results in faults and EQs
Most transform faults are found on
the ocean floor.
They commonly offset active
spreading ridges, producing zigzag plate margins, and are
generally defined by shallow
A few do occur on land.
Ex: San Andreas Fault, CA
The San Andreas is one
of the few transform faults
exposed on land.
The fault zone length is
1,300 km
The length of the fault
zone in some places
reaches tens of
kilometers wide
It slices through two
thirds of the length of
Along it, the Pacific Plate
has been grinding
horizontally past the
North American Plate for
10 million years, at an
average rate of about 5
The End :)
Up next…. Natural Disasters like
volcanoes, earthquakes, tsunamis, etc
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