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Earth’s Structure by Brainpop
Geological Changes—3:25
Looking at the world map, what do you notice
about the shape of the continents?
Jot down your ideas on your paper…
The thing is…the world didn’t always look like this!
It used to look like this:
During its early years, the
earth's outer layer was much
hotter than it is today. Over
time, the surface of the earth
cooled and hardened. Cracks
formed in the hardened
surface, creating huge plates
of rock.
Plate Tectonics Theory
 The lithosphere is divided
into a number of large and
small plates and the
plates are floating on the
mantle
Lithosphere = the Earth’s crust plus the
upper portion of the mantle layer
Where the edges of those
plates meet, the huge slabs
bash into each other, grinding,
rumpling, scraping, and
generally shoving each other
around. We experience the
more dramatic of these
encounters as earthquakes
http://earthquake.u
sgs.gov/earthquak
es/recenteqsus/
http://earthquake.usgs.gov/earthquakes/re
centeqsww/
How is this possible?!?!?
Plate motion based on The Global Positioning System (GPS)
Divergent Boundaries Create Different
Shapes on Earth
Plate Boundaries
Divergent boundary:
o Plates are moving away
from each other
o Midocean ridges are
created and new ocean
floor plates are created
Plate Boundaries
Divergent boundary:
http://library.thinkquest.org/17701/high/tect
onics/ptconv.html
Leif the Lucky Bridge Bridge between continents in Reykjanes
peninsula, southwest Iceland across the Alfagja rift valley, the
boundary of the Eurasian and North American continental tectonic
plates.
Divergent Boundary
Although the Mid-Atlantic Ridge is mostly
an underwater feature, portions of it have
enough elevation to extend above sea
level. The section of the ridge which
includes the island of Iceland is also known
as the Reykjanes Ridge. The average
spreading rate for the ridge is about 2.5 cm
per year.[
It is estimated that the Atlantic Ocean sea
floor expands at a rate of 0.5 to 4 inches
annually
Divergent Boundary
Mountain Ranges By length
Mid-Atlantic Ridge - 65,000 km
(40,389 mi)[1]
Andes - over 7,000 km (4,350 mi)
Rocky Mountains - 4,800 km
(2,983 mi)
Great Dividing Range - 3,700 km
(2,299 mi)
Transantarctic Mountains 3,500 km (2,175 mi)
Himalayas - approximately
2,400 km (1,491 mi)
Divergent Boundary
Rock outcrop in Iceland, a
visible surface feature of the
Mid-Atlantic Ridge, the
Easternmost edge of
the North American plate. It
is a popular destination for
tourists in Iceland.
Divergent Boundary
Animation
During an earthquake at a divergent fault line,
tectonic plates separate. In many cases, magma
rises from the mantle to fill in the gap or one plate
slide down to fill in the space. These types of
earthquakes usually occur in the ocean.
http://library.thinkquest.org/03oct/00758/en/disaster/ea
rthquake/faultlines.html
Convergent Boundaries Create
Different Shapes on Earth
Plates Collide
 Convergent Boundary:
plates are moving toward
each other and are
colliding
http://library.thinkquest.org/17701/high/tectonics/ptconv.html
Convergent Boundary
• Plates collide. One plate
pushes under the other.
Convergent Boundaries in Oceans
When two ocean plates
collide: Produces trenches.
Ocean trenches are deep
valleys in the ocean floor.
The Mariana Trench is
the deepest part of the
world's oceans, and the
lowest elevation of the
surface of the Earth's crust.
Convergent Boundaries in Oceans
The Mariana Trench is
the deepest part of the
world's oceans, and the
lowest elevation of the
surface of the Earth's crust.
If Mount Everest, the highest
mountain on Earth at 8,848 metres
(29,029 ft), was set in the deepest
part of the Mariana Trench, there
would be 2,062 metres (6,765 ft) of
water left above it.
When ocean plates collide with other ocean plates
In addition to trenches, ocean plates collide
and can produce volcanic islands.
Convergent Boundaries with Continents
The ocean plate
and continental
plate collides. The
ocean plate moves
underneath the
continental plate.
This forces the
land above to form
a mountain range.
Convergent Boundaries with Continents
• Mountain ranges are
created
• (example: Himalayan
Mountains)
Himalayan Mountains
Mountains 2:46
Convergent Boundaries Creates
Different Shapes on Earth
Examples
• the collision between the Eurasian Plate and the Indian Plate that is forming
the Himalayas.
• northern part of the Pacific Plate and the NW North American Plate that is
forming the Aleutian Islands.
• the Nazca Plate beneath the South American Plate to form the Andes.
• the Pacific Plate beneath the Australian Plate, and vice versa forming the
complex New Zealand to New Guinea
•collision of the Eurasian Plate and the African Plate formed the Pontic
Mountains in Turkey.
• Mariana Trench
Transform Boundaries Create Different
Shapes on Earth
Transform Plate Boundary
 The plates may move in opposite
directions or in the same
directions but at different rates
and frequent earthquakes are
created (example: San Andreas
Fault)
Transform Plate Boundary
Transform Plate Boundaries are
locations where two plates slide
past one another. The fracture
zone that forms a transform
plate boundary is known as a
transform fault. Most transform
faults are found in the ocean
Transform Plate Boundary
http://geology.com/nsta/transform-plateboundaries.shtml
Transform Plate Boundary
San Andreas Fault
The San Andreas fault is the
800 mile long boundary
between the Pacific and
North American Plates. It is
the main fault of an intricate
network of faults spanning
the California coastal region.
At its deepest, the San
Andreas extends 10 miles
beneath the ground.
Transform Plate Boundary
The San Andreas fault is a
right-lateral transform fault
meaning that if one was to
stand on one side of the
fault and look across to
the other, the opposite site
would appear to move to
the right. This means the
Pacific Plate is moving
northward while the North
American Plate is moving
southward.
http://library.thinkquest.org/03oct/00758/en/disaster/earthquak
e/faultlines.html
Plate Tectonics Theory
Plate Tectonics
Plate Tectonics Map - Plate Boundary Map
http://geology.com/plate-tectonics.shtml
So is the Earth getting bigger?
o No
o Transform boundaries neither
create nor destroy lithosphere
o Land is created with divergent
boundaries but is destroyed with
convergent boundaries.
How can Oreos model the plate boundaries?
 Very carefully, take just the top cookie off
the Oreo.
 Break the top cookie into 2 equal halves.
 Replace the cookie halves back on the Oreo
Using the cookie,
 Demonstrate a transform fault boundary
 Demonstrate a divergent plate boundary
 Demonstrate a convergent plate boundary
Seafloor Spreading Theory:
• Ocean floors are moving
like broad conveyor belts
• New ocean floor crust is
being created at the
midocean ridges
What causes this?
Convection currents within the mantle

The up-welling leg of the current creates
a divergent boundary which produces
midocean ridges
Convection Current Demo

The down-welling leg of the current
creates one type of convergent boundary
that results in trenches and a subduction
zone
What evidence do we have to support this idea?
o Midocean ridges are warmer than
surrounding ocean floors
o Active volcanoes on ridges, earthquakes
on ridges
o Midocean ridge rocks are younger than
surrounding ocean floor rocks
o Midocean ridge volcanoes are younger
than volcanoes further away
What evidence do we have to support this idea?
o Ocean floor sediments are thin on the
ridges and get thicker as the distance
from the ridges increase
o Polar reversal magnetism proves that
the ocean floor is moving away from the
ridges
Speed of Spreading

Atlantic Ocean –
2-3 cm/year

South Pacific
Ocean – 15-18
cm/year
Seafloor Spreading
The Seafloor is Spreading Clip—4:01
How Earth’s Structure Affects Plate Tectonics—5:43
Continental Drift Theory

The continents have shifted
their position over geologic
time

At one time all land masses
were connected into one piece
called Pangaea
Continental Drift Theory 3—2:21
o Pangaea began to split apart 200
million years ago
o Diagram
Laurasia
Pangaea
Gondwanaland
Pangaea—A History of the Continents: 2:23
North America
Greenland
Eurasia
West G.
East G.
Africa
S.America
Antarctica
Australia
India
The First Continents 4:57
USGS Plate
Motions Clip
Continents
o The continents are like packages on
the seafloor conveyor belt
Evidence
o High percentage fit of continents at
the 500 fathom level
Evidence
o Minerals,
fossils, and
mountains
on now
different
continents
match if
the
continents
were
together
The Mystery of Brachiosaurus (~3 min)
Evidence
o Glaciation patterns indicate a common
ice cap at the South Pole
Evidence
o Paleomagnetism (magnetism of old
rocks) indicate a common pole if the
continents were all connected
Plate Tectonics 2 –4:22
Plate Tectonics by Brainpop