sea-floor_spreading-1---introduction.ppt

Seafloor spreading and continental drift

1. Fossils of the Glossopteris Fern, a plant that
lived in warm, damp areas was found in Africa,
S. America, Australia, and in Antarctica. How
does this evidence prove Wegner’s Theory of
Continental Drift?
A: Antarctica
must have been
closer to the
equator and had
a warmer
climate.

2. •MYP Unit Question: How does land change?
•Area of Interaction: Environment
•Learner Profile: Thinker
•Standard: Investigate the scientific view of how the
Earth’s surface is formed.
•Learning Target:
I’m learning about Sea Floor Spreading because it
will help explain Wegner’s Theory of Continental
Drift.

3. •Standard: Investigate the scientific view of
how the Earth’s surface is formed.
•Learning Target:
I’m learning about Sea Floor Spreading
because it will help explain Wegner’s
Theory of Continental Drift.

4. What evidence supports the
theory of Continental Drift?
1.Shape of Continents
(Africa & S.
America)
2. Fossil evidence
(Glossopteris Fern, Mesosaurus & Lystrosaurus)
3. Rock pattern and formation
4. Climate Change (glaciers & ferns)
This was still not enough evidence!
Scientists needed a mechanism for how the
continents moved.
Opening:

5. So…Why WERE the continents
moving??
……because of sea-floor spreading!because of sea-floor spreading!
The process by
which molten
material adds new
oceanic crust to
the ocean floor.

6. •It was not until the 1950s that evidence by
different scientists helped to support the
theory of continental drift.
•Scientists began to use new technology,
such as sonar, to map the ocean floor.
•Using this technology, scientists made
new discoveries that led to the
understanding of a mechanism for
continental drift: sea-floor spreading.

7. Sonar Animation
•http://earthguide.ucsd.edu/eoc/teachers/
t_tectonics/p_sonar.html
•Sonar: A device
that determines
the distance of
an object under
water by
recording
echoes of sound
waves

8. Mapping the Ocean Floor
•Alvin’s crew found strange rocks shaped
like pillows or like toothpaste squeezed
from a tube
•Such rocks can form only when molten
material hardens quickly after erupting
under water
•The presence of these rocks showed that
molten material has erupted again and again
from cracks along the central valley of the
mid-ocean ridge.
http://www.pmel.noaa.gov/vents/nemo/explorer/concepts/pillow_lava.html

9. How does Sea-floor Spreading Work?
•a process in which new ocean floor is created as
molten material from the earth's mantle rises in
margins between plates or ridges and spreads
out.

10. Animation – Sea Floor
Spreading
•http://earthguide.ucsd.edu/eoc/teachers/
t_tectonics/p_seafloorspreading.html

11. •Samples from sea
floor drilling
showed that the
farther away from
the ridge go the
older the rocks
become.

12. Evidence to support Sea-Floor
Spreading
1.Age of the ocean floor
a. newer material was formed at the
Mid Ocean Ridge (a huge, underground mountain system).
b. older sea floor was found at the trenches.
2.Magnetic Pole Reversals (poles flipped)

13. #1 Age of the Rock
•The age of the ocean rock was
different. When scientists sampled the
rocks, they found that
a. the further away from the ridge the
rocks were, the older they were.
•b. The younger rocks were always in the
center of the ridges

14. #2 Magnetic Stripes
•Scientists discovered that the rock
that makes up the ocean floor lies in a
pattern of magnetized “stripes”
•780,000 years ago, magnetic poles
reversed themselves
•If they reversed today, the needle in a
compass would point south instead of north
•The rock in the ocean is made of iron,
which began as molten material

15. Earth’s magnetic poles have reversed
themselves throughout history.
The rocks that make up the ocean floor lie in a
pattern of magnetized stripes.

16. Sea-Floor Spreading Evidence
1.Brand new rock was found at the mid-
ocean ridge.
2.Rock got older and older the farther you
got away from the ridge. Oldest rocks
were found at the trenches.
3.Magnetic Reversals – Iron in the rocks
switched directions every time the
Earth’s polarity switched.

17. Volcanoes located along Mid-ocean
ridges erupt, creating new ocean floor.

18. Ocean Topography

19. What happens when the Ocean
crust meets Continental crust?
•http://earthguide.ucsd.edu/eoc/teachers/
t_tectonics/p_subduction.html

20. Subduction at Deep-Ocean
Trenches

21. Deep-Ocean Trenches
•Deep-Ocean Trenches: A deep valley
along the ocean floor through which
oceanic crust slowly sinks towards
the mantle

22. Subduction
•Subduction: The
process by which
oceanic crust sinks
through a deep-
ocean trench and
back into the
mantle; a
convergent plate
boundary

23. Mid Ocean Ridges
and
Deep Ocean Trenches

24. Mid-Ocean Ridge
•Mid-Ocean Ridge:
The undersea
mountain chain
where new ocean
floor is produced; a
divergent plate
boundary

25. Lithospheric Plates
What type of crust (continental or oceanic)
does the North American Plate have?

26. Sea Floor Spreading Activity with magnetic
reversals
Exit Ticket:
Where are mid-ocean ridges?
Where are trenches?