Plate Tectonics Theories

1. Plate Tectonics
Liz LaRosa for use with my 5th Grade Science Class
http://www.middleschoolscience.com 2009

2. Earth’s Layers
The Earth's rocky
outer crust solidified
billions of years ago,
soon after the Earth
formed.
This crust is not a
solid shell; it is broken
up into huge, thick
plates that drift atop
the soft, underlying
mantle.

3. The Crust
• Outermost layer
• 5 – 100 km thick
• Made of Oxygen, Silicon, Aluminum

4. The Mantle
• Layer of Earth
between the crust
and the core
• Contains most of the
Earth’s mass
• Has more
magnesium and less
aluminum and
silicon than the crust
• Is denser than the
crust

5. The Core
• Below the mantle
and to the center of
the Earth
• Believed to be mostly
Iron, smaller
amounts of Nickel,
almost no Oxygen,
Silicon, Aluminum, or
Magnesium

6. Continental Drift
Alfred Wegener 1900’s
Continents were once a single
land mass that drifted apart.
Fossils of the same plants and
animals are found on different
continents
Called this supercontinent
Pangaea, Greek for “all Earth”
245 Million years ago
Split again – Laurasia &
Gondwana 180 million years
ago
http://members.enchantedlearning.com/subjects/astronomy/planets/earth/Continents.shtml

7. Evidence of Pangea

8. Tectonic Plates

9. Plate Tectonics
• Greek – “tektonikos” of a builder
• Pieces of the lithosphere that move around
• Each plate has a name
• Fit together like jigsaw puzzles
• Float on top of mantle similar to ice cubes
in a bowl of water

10. Plate tectonics
• http://www.youtube.com/watch?v=1-HwPR_4mP4
• (7min 40 sec)

11. How Plates Move
http://pubs.usgs.gov/gip/dynamic/unanswered.html

12. How Plates Move
• Convection current – movement in a fluid or
air due to uneven cooling
1. the denser plate moves below into the earth
2. heated to liquid
3. decreases in density
4. rises to surface again
5. it cools and increases in density.

13. Different Types of Boundaries
http://pubs.usgs.gov/gip/dynamic/understanding.html

14. Divergent Boundary
• Regions where two tectonic plates are moving
apart
• Occurs between oceanic plates, continental
plates, and a combination of the two

15. Divergent Boundary –
Arabian and African Plates

16. Divergent Boundary –
Iceland
http://pubs.usgs.gov/gip/dynamic/understanding.html

17. Divergent Boundary – Oceanic
(oceanic ridge)
http://www.geology.com

18. Divergent Boundary – Continental
(rift valley)
http://www.geology.com

19. Divergent Features
• Rift valley – a long,
narrow depression that
forms when continental
crusts begins to
separate

21. Divergent: Sea Floor Spreading

22. Sea Floor Spreading
• Mid Ocean Ridges – underwater mountain
chains that run through the Earth’s Basins
• Magma rises to the surface and solidifies
and new crust forms
• Older Crust is pushed
farther away from the ridge

23. Sea-floor spreading
http://www.youtube.com/watch?v=GyMLlLxbfa4

24. Convergent Boundary
• Border formed from by the direct collision of
two plates

25. Convergent Boundary – Indian and Eurasian Plates

26. Convergent Boundary – Oceanic & Continental
http://pubs.usgs.gov/gip/dynamic/understanding.html & http://www.geology.com

27. Convergent Boundary – Oceanic & Oceanic
http://pubs.usgs.gov/gip/dynamic/understanding.html & http://www.geology.com

28. Convergent features
• Subduction zone – one plate moves under the
other
– Oceanic is more dense and moves below
continental crust at subduction zones
• Ocean trench - an elongated, sometimes arc-shaped
depression in the seafloor that can
extend for thousands of kilometers and is the
deepest part of the ocean basin as continental
and oceanic plates converge

29. Convergent features
• Island arc – chain of volcanic islands formed
along an ocean trench

30. Convergent Boundaries - Continental
http://pubs.usgs.gov/gip/dynamic/understanding.html & http://www.geology.com

31. Transform (fault) Boundary
• Boundary formed where two plates slide past
each other

32. Transform Boundary – San Andreas Fault
http://mass.pbslearningmedia.org/resource/ess05.sci.e
ss.earthsys.thrustfault/earthquakes-los-angeles/
www.geology.com

33. Review
• Name the 3 main layers of the Earth
• What is a tectonic plate?
• What was Pangea?
• What is Sea-Floor spreading?
• Name the three different types of plate
boundaries and one location on Earth for each
one