Transcript Transform Boundary

•PLATE
BOUNDARIES
•PLATE
TECTONICS
CHAPTER 7
•CONTINENTAL
DRIFT
• PANGAEA
CHAPTER 7 Sections 1-3
Why do lithospheric plates move?
1. Convection Currents: A current of
heat flows from the core to the
crust. This movement of magma
causes plates to move.
-Ridge push
-Slab pull
Tectonic Plate Theory
• The theory of plate tectonics was developed in
the 1960's.
• This theory explains the movement of the
Earth's plates (which has since been
documented scientifically) and also explains the
cause of earthquakes, volcanoes, oceanic
trenches, mountain range formation, and many
other geologic phenomenon.
• The plates are moving at a speed that has been
estimated at 1 to 10 cm per year.
• Most of the Earth's seismic activity (volcanoes
and earthquakes) occurs at the plate
boundaries.
What happens at these plate
boundaries?
• Sea-Floor Spreading- new ocean floor
created
• Volcanoes
• Earthquakes
• Mountain building
TYPES OF PLATE MOVEMENT:
Divergent, Convergent and Transform
Boundaries
• Divergent Boundary- Plates move away
from each other
• Convergent Boundary-Plates move toward
each other
• Transform Boundary- Plates move past
each other
Plate Boundaries and Movement
Divergent Boundary
• Plates move away
from each other.
• Seafloor spreading is
the movement of two
oceanic plates away
from each other,
which results in the
formation of new
oceanic crust along
the Mid - Atlantic
Ridge.
Divergent Boundary
On-land exposure of the
Mid-Atlantic Ridge in Iceland.
Iceland and the Mid-Atlantic Ridge
Mid-Atlantic Ridge or Mid-Ocean Ridge
(Divergent Boundary- Sea floor spreading)
Convergent Boundary
• When two plates collide (at a convergent plate
boundary), some crust is destroyed in the impact and the
plates become smaller. The results differ, depending
upon what types of plates are involved.
1.Oceanic Plate and Continental Plate - When a thin,
dense oceanic plate collides with a relatively light,
thick continental plate, the oceanic plate is forced
under the continental plate; this phenomenon is
called subduction zone.
2. Two Oceanic Plates - When two oceanic plates
collide, one may be pushed under the other and
magma from the mantle rises, forming volcanoes in
the vicinity.
3. Two Continental Plates - When two continental
plates collide, mountain ranges are created as the
colliding crust is compressed and pushed upwards.
Oceanic
Continental
SUBDUCTION ZONE
Oceanic
Oceanic
Volcanoes will usually form in the area.
Continental
Continental
Mountains are formed.
Transform Boundary
Two tectonic plates move past one
another.
Their edges are jagged and irregular.
As they grind together and jerk, they
slide past each other creating
earthquakes.
Transform Boundary
This is what is
happening in
California along
the San Andreas
Fault.
Two plates are
moving past each
other, causing
earthquakes.
San
Andreas
Fault,
California
Animation- Plate Boundaries
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http://www.pbs.org/wgbh/aso/tryit/tectonics/
Alfred Wegener, Pangaea and
Continental Drift
• In 1915, the German geologist and meteorologist Alfred
Wegener (1880-1930) first proposed the theory of continental
drift, which states that parts of the Earth's crust slowly drift
atop a liquid core.
• The fossil record supports and gives credence to the theories
of continental drift and plate tectonics.
• Wegener hypothesized that there was an original, gigantic
supercontinent 200 million years ago, which he named
Pangaea, meaning "All-earth". Pangaea was a supercontinent
consisting of all of Earth's land masses..
• Pangaea started to break up into two smaller supercontinents,
called Laurasia and Gondwanaland, during the Jurassic period.
By the end of the Cretaceous period, the continents were
separating into land masses that look like our modern-day
continents.
• Wegener published this theory in his 1915 book, On the Origin
of Continents and Oceans. In it he also proposed the existence
of the supercontinent Pangaea, and named it (Pangaea means
"all the land" in Greek).
This process
of continental
drift took
place over
MILLION of
years
Evidence Supporting Continental
Drift
• The Shapes Match
• The Plants and Animals Match
• The Rocks Match
The Shapes Match
The continents look as
if they were pieces of a
giant jigsaw puzzle that
could fit together to
make one giant supercontinent.
The Plants and Animals Match
Wegener noted that plant fossils of late Paleozoic age found on several different continents were
quite similar. This suggests that they evolved together on a single large land mass. He was
intrigued by the occurrences of plant and animal fossils found on the matching coastlines of
South America and Africa, which are now widely separated by the Atlantic Ocean.
The Rocks Match
Broad belts of rocks in Africa and South America are the same type. Broad
rock belts in North America, the British Isles and Scandinavia match. These
broad belts then match when the end of the continents are joined.
The Importance of Wegener’s Work
• Since Wegener's day, scientists have mapped and explored the
great system of oceanic ridges, the sites of frequent earthquakes,
where molten rock rises from below the crust and hardens into new
crust.
• We now know that the farther away you travel from a ridge, the older
the crust is, and the older the sediments on top of the crust are. The
clear implication is that the ridges are the sites where plates are
moving apart.
• Where plates collide, great mountain ranges may be pushed up,
such as the Himalayas; or if one plate sinks below another, deep
oceanic trenches and chains of volcanoes are formed. Earthquakes
are by far most common along plate boundaries and rift zones:
plotting the location of earthquakes allows seismologists to map
plate boundaries and depths.
• Paleomagnetic data have allowed us to map past plate movements
much more precisely than before. It is even possible to measure the
speed of continental plates extremely accurately, using satellite
technology.
• Nevertheless, Wegener's basic insights remain sound, and the lines
of evidence that he used to support his theory are still actively being
researched and expanded.
Links and Animations
http://library.thinkquest.org/17457/english.h
tml Great site, Games and Activities
http://www.platetectonics.com
http://geology.com/plate-tectonics.shtml
http://www.wwnorton.com/college/geo/ege
o/animations/ch2.htm
http://sio.ucsd.edu/voyager/earth_puzzle/
Fossil Animation
Key Terms for 7.1,7.2 and 7.3
Theory of Plate Tectonics
Theory of Continental Drift
Pangaea
Crust, Mantle and Core
Lithosphere
Asthenosphere
Convection Current
Convergent Boundary
Divergent Boundary
Transform Boundary
Subduction zone
Mid-Ocean Ridge (Mid- Atlantic Ridge)
Sea-Floor Spreading
QUIZ
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1. Boundary where two plates move away from each other_____________
2. Boundary where two plates move toward each other_________________
3. Boundary where two plates move past each other ________________
4. When two oceanic plates move away from each other it is called_______.
5. When an oceanic plate moves below a continental plate a_____zone is created.
6. The underwater chain of mountains in the Atlantic ocean caused by a divergent
boundary is _____.
7. Theory that states that all of the continents were one large land mass millions of years
ago is__________.
8. The theory that explains the movement of tectonic plates is_______.
9. The giant land mass that Wegener says existed millions of years ago is called________.
10. Made of crust and upper mantle_________.
11. Is made up of tectonic plates_________.
12. Consists of mantle, tectonic plates move on top of this_________.
13. A current of heat flows from the core to the crust. This movement of magma causes
plates to move. _____________.
14. Outermost layer of the Earth_________.
15. Contains most of Earth’s mass___________.
16. Center of the Earth that is made mostly of iron and nickel___________.