Transcript Chap7Sect3-plate tectonics

Ch.7.3 (New Book)
Theory of Plate
Tectonics
The Theory of Plate Tectonics
Objectives: (copy me down in your IAN)
1. What is plate tectonics?
2. Where does the FORCE come from to
move the tectonic plates?
3. Describe the three types of plate
boundaries.
4. Review, what are subduction zones?
Let’s Read more about it!
1) p. 194-195 out loud,THEN:
2) Answer, how are tectonic
plates like ice cubes in a punch
bowl?
3) Let’s compare your tectonic
plate maps. (pic on next page)
4) How many plates are covered
in BOTH land and water?
Oceanic and Continental Crusts
Tech Terms: (copy these down)
1. plates – separate sections of the
lithosphere.
2. plate tectonics – a geological
theory that states that pieces of
the Earth’s lithosphere are in
constant, slow motion, driven by
convection currents in the
mantle.
Take out the new map from your
blue tub. Using p. 194. complete the
instructions on this new map. An
example picture is on the next page!
The 10 top Tectonic Plates!
• These plates are created by faults –
breaks in Earth’s crust where plate
boundaries form.
Remember the Ring of Fire? How does it effect
one of the largest plates on our planet?
Ch.7, Sect.3
• The theory of Plate Tectonics: What are
the boundaries and how do they move?
• Read aloud p. 202-203 and discuss.
Tech terms, copy these down!
4) convergent boundary – the place
where two plates come together, or
collide. (the density of the plates
dictates which one comes out on
top).
Oceanic crust (basalt rock) is more dense
Continental crust (granite rock) is less dense
5. divergent boundary – the place
where two plates move apart, or
dive away (most occur at the midocean ridge).
6. rift valley – develops on land,
where two plates diverge.
7. Read and discuss the picture at
the bottom of page 202-203.
7. transform boundary –
a place where two
plates slide past
each other in
opposite directions.
Read and discuss p.204-205.
• Possible Causes of Tectonic Plate
Motion?
• Tracking Plate Motion?
• Read and discuss figure 1.
• Complete Section Review Questions in
your IAN.
• 3 “Big Ideas from yesterday”
• Sea-floor spreading and subduction can
change the size and shape of the oceans.
• The Pacific Ocean, aka The Ring of Fire,
has lots of subduction zones, thus it is
getting smaller.
• The Atlantic Ocean is expanding.
Further Evidence for Sea-Floor
Spreading:
• Magnetic Reversals!
• The molten rock at the mid-ocean ridges
contains tiny grains of magnetic minerals.
These mineral grains contain iron and are
like compasses.
• They align with the magnetic field of the
Earth. When the molten rock cools, the
record of these tiny compasses remains in
the rock.
• This record is then carried slowly away
from the spreading center of the ridge as
sea-floor spreading occurs.
• As you can see in Figure 5, when the
Earth’s magnetic field reverses, the
magnetic mineral grains align in the
opposite direction.
The polarity of Earth’s magnetic
field changes over time.
• The new rock records the direction of the
Earth’s magnetic field. As the sea floor
spreads away from a mid-ocean ridge, it
carries with it a record of magnetic
reversals.
• This record of magnetic reversals was the
final proof that sea-floor spreading does
occur.
Magnetic reversals in oceanic crust are shown as
bands. Light blue is when the poles have normal
polarity. Dark blue indicates reverse polarity.