The document discusses the theory of seafloor spreading, where new ocean crust is formed at mid-ocean ridges as tectonic plates move apart, and magnetic patterns in rocks on the ocean floor provide evidence of periodic reversals of the Earth's magnetic field. Analysis of magnetic stripes on both sides of ocean ridges that appear to be mirror images supports the idea that the seafloor is actively spreading.

1. Harry Hess

2. Recall:
 Scientists know Earth’s interior is made
mostly of layers of _______________.
 Some layers, like the center part, called the
______are hard and______.
 Other layers are not. The layer next to the
center, called the_________, is _______.
Both parts of the core are made
of___________.
inner core; liquid ; rock
iron and nickel; outer core;
solid

3. Recall:
 The largest layer inside Earth is called the
_____. It’s neither completely solid nor
completely liquid, but_____. It’s
extremely______.
 Earth’s outermost layer is the______ . This
layer is about 5 km thick under the_______
and up to 35 km thick under the______.
 On top of the outer layer is the weathered
rock called______.
continents ; mantle; plastic like
crust; oceans; soil; hot

4. Despite the evidences
presented by Wegener, WHY
was his idea that the
continents were once joined
together was not accepted by
the scientific society?
This made scientists conduct
further studies in search for the
answer.

5. 1950s and 1960s- new
techniques and modern
gadgets
sonars and submersibles
scientists had a clearer view of
the ocean floors
discovered underwater
features deep within the ocean

6. a system of ridges or
mountains in the seafloor
similar to those found in the
continents (mid-ocean ridges)
Mid-Atlantic Ridge: an undersea
mountain chain in the Atlantic
Ocean
a gigantic cleft about 32-48 km
long and 1.6 km deep

7. Mid-Atlantic
Ridge

8. Activity 5: Split and Separate!
Simulate and describe the
seafloor spreading process.
• Realize the importance of the
seafloor spreading process
relative to the Continental Drift
Theory.

9. Paper
Folder

11. Answer:
Q22-27

12. Describe and explain
each
diagram/illustration.

13. Harry Hess

15. Magnetometer

18. Sea Floor Spreading
 early 1960’s- Harry Hess, together with
Robert Dietz
 Seafloor Spreading Theory
 hot, less dense material from below the earth’s
crust rises towards the surface at the mid-ocean
ridge
 material flows sideways carrying the seafloor
away from the ridge, and creates a crack in the
crust
 magma flows out of the crack, cools down and
becomes the new seafloor

21. Sea Floor Spreading
 allowed the creation of new bodies of water
 the Red Sea -African plate and the
Arabian plate diverged
 pulling Australia, South America, and
Antarctica away from each other in the
East Pacific Rise
 The East Pacific Rise -the most active
sites of seafloor spreading, more than
14 cm/yr

22. SFS
 rate of formation of a new seafloor is not always
as fast as the destruction of the old seafloor at
the subduction zone
 explains why the Pacific Ocean is getting
smaller and why the Atlantic Ocean is getting
wider
 If subduction is faster than seafloor spreading,
the ocean shrinks
 When the seafloor spreading is greater than the
subduction, then the ocean gets wider

24. The SFS contradicts a part of the
CDT
CDT- continents moved through
unmoving oceans and that larger,
sturdier continents broke through the
oceanic crust
Whereas, the seafloor spreading
shows that the ocean is the actual
site of tectonic activity

25. Findings that support Seafloor Spreading Theory:
Rocks are younger at the mid-ocean
ridge.
Rocks far from the mid-ocean ridge
are older.
Sediments are thinner at the ridge.
Rocks at the ocean floor are younger
than those at the continents.

26. Bring the ff:
 Pencil
 Ruler

27. Activity 6: How fast does it go!
Objectives:
• Analyze a magnetic polarity
map.
• Use legends and scales of the
map properly.
• Calculate the rate of seafloor
spreading using magnetic clues.

28. VISIT, EXPLORE, ANSWER
 http://www.montereyinstitute.org/noaa/lesson02/l
2la1.htm
 http://earthguide.ucsd.edu/eoc/teachers/t_tectonic
s/p_seafloorspreading.html

29. Answer:
 Q28-29

30. Magnetic Reversal
magnetic ‘flip’ of the Earth
the North Pole is transformed into
a South Pole and the South Pole
becomes the North Pole
due to the change in the
direction of flow in the outer
core

31. Magnetic Reversal
 explained through the magnetic patterns
in magnetic rocks, especially those found
in the ocean floor
 When lava solidifies, iron bearing
minerals crystallize
 the minerals behave like tiny compasses
and align with the Earth’s magnetic
field so when magnetic reversal occurs,
there is also a change in the polarity of
the rocks

32. Describe and explain each
diagram/illustration.

40. Age of Oceanic Crust

41. Divergent: Iceland

42.  Over the last 10 million years, there has
been an average of 4 to 5 reversals per
million years.
 New rocks are added to the ocean floor
at the ridge with approximately equal
amounts on both sides of the oceanic
ridge.
 The stripes on both sides are of equal
size and polarity which seemed to be
mirror images across the ocean ridge.

43. What does this
indicate?
It indicates that
indeed, the seafloor
is spreading.

44. NET RESULTS
 Spreading rates at transform faults
 Pacific plate moves NW at 8 cm/yr
 N American plate moves W at 2 cm/yr
 Indian plate moves NE at 12 cm/yr
 Pacific Ocean is shrinking and Atlantic
is growing
 Atlantic opened about 200 MY ago so there
should be no rocks older than this in the
Atlantic

45. Most recent episode
of
Seafloor spreading:
Pangaea first broke
into 2 pieces
Sea opens between N
and S continents and
Between Africa and
Antarctica
India moves North

46. S Atlantic opens
Antarctica moving S
India moving N
Australia separates
and moves N

47. 50 MY in the future:
1. Africa will move N and
close Mediterranean Sea
2. E Africa will detach (Red
Sea rift zone) and move to
India
3. Atlantic Ocean will grow
and Pacific will shrink as it
is swallowed into Aleutian
trench.
4. W California will travel
NW with the Pacific Plate (LA
will be swallowed into the
Aleutian trench in 60 MY).

48. Bring the ff: (by group)
dropper
food color
3-5 small / light wood
blocks
(or sponge cut into thin and
small blocks)