Download Drifting Continents

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The red triangles mark the location of ?????
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Chapter 17 Plate Tectonics: Objectives
1.
Describe early evidence that led people to suggest that Earth’s
continents may have once been joined.
2. Discuss evidence of continental drift.
3. Explain why continental drift was not accepted when it was first
proposed.
4. Summarize the evidence that led to the discovery of seafloor spreading.
5. Describe the uses of magnetometers and sonar.
6. Explain the significance of magnetic patterns on the seafloor.
7. Explain the process, cause, features and evidence of seafloor
spreading.
8. Explain the theory of plate tectonics.
9. Compare & contrast the 3 types of plate boundaries and their features,
location, & direction of movement of each. (Features include:
subduction, trenches, ridges, mountains, islands)
10. Explain the process of convection.
11. Summarize how convection in the mantle is related to the movements
of tectonic plates.
12. Miscellaneous vocabulary: Pangea, early mapmakers, Wegener.
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Why are they there??
Chapter 17 – Plate Tectonics
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Drifting Continents
In a an average lifetime it does not look like the surface of Earth
is changing, with the exception of earthquakes, volcanic
eruptions, and landslides.
On the geologic time scale Earth is always changing
1. South America is moving away from Africa at a rate of 2 to
3 cm/y and Hawaii is moving to the northwest at 8 to 9
cm/y
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Sec 17.1 Drifting Continents – Earliest Evidence
Alfred Wegener
1. Early mapmakers noted that the coastlines of continents
appeared to fit together like a puzzle, especially the
southern continents; South America and Africa.
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1. Alfred Wegener proposed the theory of Continental Drift
2. Continental Drift theory: All continents were originally joined
as a single landmass called Pangaea.
A. Wegener proposed that Pangaea began to break up 200
million years ago and began drifting apart
B. The process is still occurring.
3. Wegener’s evidence for continental drift went beyond the
“puzzle fit” the map-makers had seen.
Wegener collected evidence to support his ideas from:
A. Rocks
B. Fossils
C. Climatic Data
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Fig 17-2 p 445 Evidence of Continental Drift
What evidence would support the hypothesis of Continental Drift?
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4. Evidence from Rocks: Similar rock types between:
A. Appalachian mountains in U.S. & rocks in Greenland
B. S. America & Africa
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5. Evidence from Fossils: Similar fossils & plants have
been found on widely separated continents:
Kannemeyerid & Labyrinthodonts were land-dwelling animals that could
NOT have swam the ocean
B. Mesosaurus: fresh-water reptile that could not have crossed the ocean
C. Glossopteris: Fern found on many continents that now have different
climates
Continents must have once been joined & had a similar
temperate (mid-latitude like us) climate to grow the fern
Antarctica must have been closer to the equator to have a
warm enough climate to grow the fern
A.
http://www.energymarketwatch.net/images/vikpangeamap.jp
g
http://www.geology.ohiostate.edu/~vonfrese/gs100/lect25/xfig25_09.jpg
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6. Ancient Climatic Evidence
A. Coal deposits have been found in Antarctica
It forms from dead swamp plants. Swamps only occur
in an area that is wet and spongy
This indicates that Antarctica was once warmer and
wetter, closer to the equator
B. Glacial deposits in Africa, India, S. America, and Australia
This suggests that these areas were closer to the S.
http://1.bp.blogspot.com/_vrThsGmakQU/TLbfZ4BFvdI/AA
AAAAAAAFA/XLv8g0rnZBk/s1600/IMGete.jpg
Pole at one time
7. Problems with Wegener’s Continental Drift Theory
Problems caused it to be rejected in the early 1900’s because of
these 2 “flaws”:
A. Wegener couldn’t explain what caused the caused the
continents to move
B. Wegener couldn’t explain how the continents could
move without shattering
C. Ideas about the ocean floor were wrong until the mid1900s. Scientists thought the seafloor was flat, older
then the continents and unchanging-ALL WRONG.
http://ebooks.cambridge.org/cont
ent/978/05/1184/236/8/97805118
42368i.jpg
http://www.ruf.rice.edu/~leeman/CarbCoal.gif
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New Discoveries & Ideas About the Seafloor
(Sec 17.2 Seafloor Spreading
1. Sonar – new technology. Big advancement.
A. Calculated the distance to the seafloor using the time it
took for reflected sound waves to return
2. Magnetometer: Measures small changes in magnetic fields
A. Used to make maps of the magnetic fields in rocks on the
sea floor.
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http://image.slidesharecdn.com/7thgrade-ch-1sec3driftingcontinents-100824072350-phpapp01/95/7th2/16/2016
3. Ocean Floor Topography
A. Ocean ridges contain the longest mountain range on Earth
i. Earthquakes & volcanoes occur along the ridges
B. Deep-sea trenches are narrow & elongated depressions with
very steep sides
i. Deepest trench: Marianna trench is over 11km deep
http://home.earthlink.net/~dengelhardt/images/zonesmedium.jpeg
http://aegisinstruments.com/images/products/gsm
p30a1.jpg
http://www.whoi.edu/cms/images/oceanus/20
06/4/abe1en_23508.jpg
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http://www.deepseachallenge.com/wp2/16/2016
content/uploads/2012/03/mariana-trench-graphic-30812.jpg
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4. Ocean Rocks and Sediments
A. Rocks near the ridges are the youngest, age increases with
distance from the ridge
B. Oceanic rocks are much younger than continental rocks
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TT #48 & Fig 17-11 p453: Isochron Map of Floor
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http://www.ngdc.noaa.gov/mgg/ocean_age/data/2008/image/age_oc
eanic_lith.jpg
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5. Paleomagnetism
Paleomagnetism: magnetic record of rocks containing iron
A. Basalt contains iron minerals which get “stuck” pointing
towards Earth’s magnetic pole as it cools & hardens
B. The iron minerals show a pattern of magnetic reversals
which indicate a change in Earth’s magnetic field
http://www.brockpress.com/wpcontent/uploads/2014/10/magneticfield.gif
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Fig 17-10 p 452 Magnetic Field Reversals
Seafloor Spreading Theory
1.
Seafloor Spreading Theory: SUMMARY: New ocean crust is formed at
ocean ridges & is destroyed at deep-sea trenches
A. Proposed by Harry Hess
B. Magma is hotter & less dense at the mid-ocean ridge, so it fills the gap in
the ridge
C. Magma in the gap cools, forming new ocean floor
D. More & more magma rises & hardens, forcing the previous rock to move
away from the ridge
E. Therefore, younger rock is near the ridge & age increases farther from
the ridge
F. Theory provided answers to the 2 flaws of Wegener’s Continental Drift
hypothesis
i. Seafloor spreading caused the landmasses to move
ii. Landmasses didn’t shatter because they weren’t plowing through the
ocean crust. Rather, the ocean floor & continents moved together
http://earthguide.ucsd.edu/eoc/t
eachers/t_tectonics/p_seafloors
preading.html Link to animation
of seafloor spreading
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TT #48 & Fig 17-11 p453: Isochron Map of Floor
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Sec 17.3 Theory of Plate Tectonics & TT#48/Fig 17-11 p.453
Theory states that the Earth’s crust & ridged upper mantle are
broken into enormous slabs called plates.
Plates move in different directions and at different rates.
Plate Boundaries = Where tectonic plates interact
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Plate Boundaries: 3 Main Types
QUESTIONS:
• What areas have the highest number volcanoes?
• What do you think causes such a high number of volcanoes in specific areas like
that?
• Is it related to the type of boundary present? We’ll find out!
1. Divergent
2. Convergent
3. Transform
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2nd Type of Divergent Boundary – Rift Valley
Divergent Boundaries
Divergent Boundaries: Plates move apart
There are 2 subtypes of divergent boundaries, depending
on their location:
A. Mid-Ocean Ridge forms if the divergent boundary is
underwater
Mid-Ocean Ridge is a long mountain chain with
volcanoes
Causes the ocean basin to widen.
B. Rift Valley forms if the divergent boundary is on land
As the continent is torn farther and farther apart, the rift
valley gets deeper and deeper.
It may eventually fill with water and become an ocean
Example Rift Valley Locations: Iceland & East Africa
http://upload.wikimedia.org/wikipedia/common
s/thumb/5/56/Ridge_render.jpg/270pxRidge_render.jpg
http://geology.com/nsta/divergent-plate-boundaries.shtml -Link
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to animation
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Divergent/widen Boundaries – Additional General Info
C. BOTH types of divergent boundaries add(create) new crust
D. Divergent boundaries widen ocean basins and
lengthen/widen earth’s surface
C. The Atlantic Ocean is widening an average of 2-3cm /
year.
E. Volcanoes and earthquakes are common along both rift
valleys and mid-ocean ridges
F. Explains why young rock is in the middle of the ocean and
older rock near the continents.
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Convergent Boundaries
2. Convergent Boundaries: Plates collide & move towards
each other.
A. Subduction MAY occur: One plate descends below the
other
Destroys & recycles crust material
Due to differences in density
May create deep-sea trenches, volcanoes & volcanic
islands – depending on where the boundary is located
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http://www.geo.cornell.edu/hawaii/220/PRI/images/subduction2.jpg
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1st Subtype Convergent -Oceanic meets Oceanic
Fig 17-15 p457 Convergent Diagrams
What type of crust MUST be present for subduction to occur?
3 subtypes of Convergent Boundaries
1. 1st subtype of Convergent: Oceanic meets Oceanic
http://geomaps.wr.usgs.gov/parks/pltec/ocnvsocn289x
151.gif
Link to animation: http://geology.com/nsta/convergent-plate-boundaries.shtml
1.
Subduction occurs
The cooler & denser oceanic plate descends below the less dense
oceanic plate
A. Forms deep-sea trenches, island arcs, volcanoes & deep focus
earthquakes
B. Example locations:
Mariana Trench & Islands
Aleutian Islands near Alaska
Japan & Phillipines
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2nd Type Convergent -Oceanic meets Continental
2.
Diagram: Convergent Oceanic-Continental
2nd Subtype of Convergent: Oceanic meets Continental
http://4.bp.blogspot.com/Q6aPHSFLitk/UGinkzRAR5I/AAAAAAAAKG4/GToi6bna8Ak/s1600/peruchile-trench.gif
http://geology.com/nsta/convergent-plate-boundaries.shtml
1. Subduction occurs.
Dense ocean plate descends below the less dense continental plate
Ocean plates are dense because they are made primarily of basalt
Continental plates are less dense because they are made primarily of
granite
A. Forms deep-sea trenches along the edge of continents
B. Mountain ranges, volcanoes, deep focus earthquakes may occur along the
continental edge above the subduction zone
C. Example locations: Peru-Chile trench & Andes Mountains along western
edge of South America
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3rd Subtype Convergent: Continental meets Continental
3.
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Comparison of All 3 Types Convergent
Continental meets continental
http://bc.outcrop.org/images/tectonics/press4e/figure-02-09c.jpg
http://geology.com/nsta/convergent-plate-boundaries.shtml
Subduction does NOT occur
Both continental plates are too buoyant due to low density
Therefore, there is NO melting & NO volcanoes
B. HIGH mountain ranges, extremely folded
C. Earthquakes present
D. Example location: Himalayas
A.
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http://i.ytimg.com/vi/R-40Z2YaZ6M/maxresdefault.jpg
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2.
San Andreas Fault Pictures
http://hoopmanscience.pbworks.com/f/1348757835/t
ransform_20boundary.jpg
http://geology.com/articles/san-andreasfault.shtm
Transform Boundaries: 2 plates slide horizontally past each other
A. Crust is NEITHER consumed or created, only deformed or
fractured
B. Creates long faults & shallow earthquakes
i. Fault = Fracture in Earth’s crust along which movement occurs
C. Can move opposite directions, OR the same direction at different
rates
D. Example locations: San Andreas fault. Most are along ocean
ridges.
http://news.nationalgeographic.com/news/bigphotos/29897277.html
Transform Boundaries
http://208.93.184.5/~jones/Geology/pictures/plates/transform.jpg
http://earthsciencepd5.wikispaces.com/file/
view/faultPict.gif/186467883/390x308/fault
Pict.gif
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Famous Transform Boundary!
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TT #50 Types of Plate Boundaries
http://geology.com/nsta/transform-plate-boundaries.shtml
Describe the location of San Francisco in relationship
to Los Angeles:
•Now?
•Thousands of years from now, if the plates keep
moving?
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TT #49 & Fig 17-13 p 455
Diagram – Relationship Between
All 3 Types of Plate Boundaries
http://www.rhnet.org/webpages/jpeck/photos/38683/2PlateBoundaries.jpg
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Sec 17.4 Causes of Plate Motions
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Mantle Convection Currents in the Asthenosphere
Convection: The transfer of thermal energy by the movement of
heated matter
1. Warms, expands, and becomes less dense & rises
2. Cooler, denser material sinks due to gravity
3. Forms a cycle or convection current
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1. What the boundary between the African & Antarctic plate, what direction is African
moving? African & North American plate – direction of African??
2. Name place likely to have earthquakes. Name one not likely to have earthquakes.
3. Do same for volcanoes.
(Questions like these on exam)
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1. Convection in the aesthenosphere is thought to cause the
plate movements
A. Asthenosphere is soft & pliable layer of the mantle that
flows and allows the plates to move
B. Hot mantle material is less dense & rises, as it cools it
sinks again
http://www.coolgeography.co.uk/GCSE/AQA/Restless%20Earth/Tectonics
/Earth_Structure_Diagram.png
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http://skyblue.utb.edu/paullgj/physci1417/Lectures/Convection.JPG
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Convection Relationship to Type of Boundary
Diagram of Convection & Plate Boundaries
2. Rising part of the current occurs at divergent boundaries
A. Causes upward & lateral forces that split the lithosphere
B. As plates separate, rising magma cools & forms new
ocean crust
3. Sinking part of the current occurs at convergent boundaries,
pulling plate material down
A. Sometimes forms deep-sea trenches
http://www.thegeographeronline.net/uploads/2/6/6/2/26629356/2378764_orig.jpg
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Bellringer #1:Review of Section 17.1 & Video
1. What theory suggests that South
America and Africa were once part of a
larger continent that broke and moved
apart?
2. Who was the German scientist who
proposed the most famous version of
this theory?
3. List 3 lines of evidence he used to
support his theory.
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Bellringer #2
1. Thinking Critically: Oil deposits approximately 200 million
years old have been discovered in Brazil. Where might
geologists find oil deposits of a similar age? Explain.
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Bellringer #3
1. Magnetic minerals in undisturbed rocks on the ocean floor will:
A. Indicate where magnetic pole was at the time of formation
B. Align with “north” as we know it to be now, no matter what
C. Change in their direction of alignment slowly over time
2. How do glacial deposits in Africa, India, Australia, and South
America support the idea of continental drift?
3. THINKING CRITICALLY: Why are the magnetic bands in the
eastern Pacific Ocean so far apart compared to the magnetic
bands along the Mid-Atlantic Ridge?
Bellringer #4
1. What do we know about the distribution of earthquakes &
volcanoes on Earth?
A. They occur randomly across the world
B. Quakes tend to happen along plate boundaries but
volcanoes are random
C. Both quakes & volcanoes tend to occur at plate boundaries
2. If sea floor spreading centers create new crust constantly,
does that mean the earth is getting bigger? Explain.
3. Describe the age of rocks at a mid-ocean ridge.
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Bell Ringer # 5
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Plate Boundary Review
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Bellringer #6 Evidence & Features at Boundaries
Are the following features typical for an oceanic to
oceanic convergent boundary?
A = Usually present
Look at the circled boundary:
1. What type of boundary is it?
2. What are 3 landforms or movements that are likely to be
present?
3. Explain a convection current.
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1.
2.
3.
4.
5.
B = Not usually present
Volcanoes
Ocean ridge
Folded mountains
Subduction
Rift valley
6. What evidence suggests that Africa & India were once
closer to the South Pole?
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Bellringer #7
Bellringer #8
1. How will lithospheric plates that are directly above a rising
current move?
• Together or apart?
2. How will a plate above a sinking current move?
• Together or apart?
3. Use ONE word to describe the
A. Lithosphere:
B. Aesthenosphere
4. Which contains the plates? Lithosphere or Aesthenosphere?
5. Which has convection currents? Litho or Aesthenosphere?
6. Which has oceanic crust? Lithosphere or Aesthenosphere?
7. Which is hotter? Lithosphere or Aesthenosphere?
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What type of plate boundary is it IF???
1. Plates are pulling apart
2. Plates are sliding past each other
3. Boundary where you will see mountains
4. Boundary that creates mid ocean ridges
5. San Andreas Fault
6. Mid-Atlantic Ridge
7. Where we see lots of quakes and volcanic
activity
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Bellringer #9
Bellringer #10
1. What type of boundary produced the San Andreas Fault?
2. What is a famous example of a divergent boundary?
Label the tectonic plates
3. What type of boundary produced the Himalayas? Where are
they located?
4. Give a famous example of a subduction boundary. List the
continental and oceanic crusts involved.
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