Transcript Chapter 33

Thursday, October 29
• Word of the Day:
– Theory of plate tectonics: Earth’s outer shell,
the lithosphere, is divided into plates that ride
on the asthenosphere
• Warm-Up:
– If you were a scientist trying to prove that the
earth is round, what evidence would you
give?
Monday, November 2
• Divergent boundary: two plates move
away from one another
• Warm-Up:
– Cut out the pieces of the puzzle and try to
piece the continents together to form one
large continent.
– What is this continent called?
– What has caused the continents to move to
where they are now?
11/4
• Word of the Day:
– Convergent Boundary: two plates move
toward one another; collide
• Warm-Up:
– Summarize the 5 pieces of evidence Wegener
proposed for the Theory of Continental Drift
Chapter 33
Our Restless Planet
33.1 The Theory of Continental
Drift
• Pangaea
–
Scientists noticed that the eastern
shorelines of South America and the
western shoreline of Africa fit like a puzzle
– Alfred Wegener proposed that all continents
had once been one big land mass
• Pangaea – supercontinent that once existed
• Broke into several large pieces
Evidence
• Geological boundary of continent at continental
shelf
–
continental shelf – gently sloping platform between the
shoreline and the steeper slope that leads to the deep
ocean floor
• Rocks from different continents match
• Mountain systems in Africa and South America
•
show evidence of having once been joined
Identical fossils have been found on different
continents
Evidence
• Paleoclimatic evidence
– Ice once covered parts of several continents
– If in present positions, would have covered whole world
– No evidence of very cold climate then, but if one
continent, the ice evidence makes sense
• Idea thrown out during Wegener’s time,
but widely accepted today
Scientific Revolution
–
Paleomagnetism – magnetism changes from
the past seen in geology
• From rocks that form near the earth’s magnetic
•
•
field, we can determine where the magnetic
poles have been over time
Scientists discovered that the magnetic poles
have moved all over the world
Provided proof the continents had drifted
Mapping of Ocean floors
• Found huge mountain ranges, deep ocean
•
trenches, and volcanic activity
H.H. Hess proposed seafloor spreading
–
–
–
–
Seafloor constantly made new
Underwater mountains form convection cells moving up
New lithosphere forms at Mid-ocean ridges
Earth Recycled
11/5
• Subduction: one plate slides underneath
another
• Warm-Up:
– Which type of plate boundary would form
mountains?
– Why?
– Which type would form big valleys?
– Why?
Calculation Corner
• We can use calculations to figure out how
fast things are moving or spreading.
• With your group, do the calculation corner
on page 596 in the book.
– Look through the example
– Then, answer the “Your Turn” questions at
the bottom
Thursday, November 5
• Word of the Day:
– Transform fault boundary: two plates move
horizontal (side-side) relative to one another
• Warm-Up
– Brainstorm: What are some structures on
earth that could have been formed from plate
boundaries?
33.2 The Theory of Plate Tectonics
• Theory of Plate Tectonics – Earth’s outer shell,
•
•
•
the lithosphere, is divided into 8-12 large
plates and a number of smaller ones
Lithospheric plates float on the plastic
asthenosphere
Interiors of plates are stable
All interactions occur along plate boundaries;
why we see earthquakes, volcanoes, and
mountains at similar places
33.3 There are 3 Types of Plate
Boundaries
• Divergent Boundaries
– Two plates are moving apart
– Created by tension forces
• Convergent Boundaries
– Plates come together
– Created by compression forces
• Transform-fault Boundaries
– Plates slide horizontally past each other
Divergent Boundaries
– Mid-Atlantic Ridge:
spreading center, making
Atlantic Ocean grow
• Ground younger near the
ridge, older as you move
away
• Spreads at about 2 cm a year
– Rifts or Rift Valleys:
spreading centers on land
• Example: Great Rift Valley of
East Africa
• May become a new ocean
basin one day
Convergent: Oceanic-Oceanic
• Subduction occurs: One plate drops below
the other one
– Forms a deep ocean trench
– Crust deep in trench melts, produces magma
which can lead to volcanic island arcs
Convergent: Oceanic-Continental
• More dense ocean plate goes below the
less dense continental plate (subduction)
• Forms chains of volcanic mountains on the
continental plate
– Ex: Andes in South America, Sierra Nevada
and Cascade Ranges in the Western US
Convergent: ContinentalContinental
• Compression causes breaks
and folds in both plates
– Crust is very thick
– No volcanoes, but lots of
earthquakes
• Produces Mountain Ranges
– Ex: Himalayas in Asia and the
European Alps
Transform-Fault Boundaries
• Lithosphere is not created or
•
•
destroyed
Same motion as strike-slip faults
San Andreas Fault is most famous
Transform-Fault
– Pacific plate moves North about 5
cm a year
– San Andreas responsible for about
3.5 cm of that 5
33.4 The Theory that Explains
Much
• Plate Tectonics directly relates to rock types and
•
•
•
formation
Metamorphic rocks form in areas of subduction
and continental collisions
Melting ocean floor creates magma, when it
cools it produces Igneous rock such as granite
or basalt
Sedimentary rocks form from the weathering of
mountains, which are formed by plate tectonics.
Review:
• Hold up a:
– 1 for Divergent
– 5 for convergent
– 10 for Transform fault
Questions
• San Andreas is an example of this
– 10
• Causes mountain ranges
–5
• Could create a new island in Africa
–1
• Creates Rift Valley and mid-ocean ridges
–1
Questions
• Creates volcanic island arcs
–5
• No earth is created or destroyed
– 10
• Caused by tension forces
–1
• Horizontal (side-to-side) movement
– 10
11/12
• Take out your homework and homework
calendar…Have them out and ready
• Word of the day:
– Rifts: large down-faulted valleys created by
spreading centers
• Warm-Up:
– A woman sits in the warmth of a natural hot
spring located in the quiet and peaceful
mountains. How is that spring warmed?
Monday, November 9
• Rift Valley: large down-faulted valleys
created by spreading centers
• Warm-Up:
– Get a map off the front desk. At each of the 3
locations given on the map, tell me what you
would be wearing
– Explain the difference between longitude and
latitude.
Tuesday, November 10
• Mineral: a naturally occurring, solid
substance made of only one element or
compound
• Warm-Up: Explain how the different plate
boundaries form mountains, volcanoes,
and volcanic islands
– List any veterans or current military people
that you know…Be sure and thank them for
serving our country!