structured of earth

1. The Structure of the Earth and
Plate Tectonics

2. Structure of the Earth
• The Earth is
made up of 3
main layers:
– Core
– Mantle
– Crust
Inner core
Outer core
Mantle
Crust

3. The Crust
• This is where we live!
• The Earth’s crust is made
of:
Continental Crust
- thick (10-70km)
- buoyant (less dense
than oceanic crust)
- mostly old
Oceanic Crust
- thin (~7 km)
- dense (sinks under
continental crust)
- young

4. What is Plate Tectonics?

5. • If you look at a map of the world, you may notice that some of the
continents could fit together like pieces of a puzzle.

6. Plate Tectonics
• The Earth’s crust is divided into 12 major
plates which are moved in various directions.
• This plate motion causes them to collide, pull
apart, or scrape against each other.
• Each type of interaction causes a
characteristic set of Earth structures or
“tectonic” features.
• The word, tectonic, refers to the deformation of
the crust as a consequence of plate
interaction.

7. World Plates

8. What are tectonic plates made of?
• Plates are
made of rigid
lithosphere.
The lithosphere is
made up of the
crust and the upper
part of the mantle.

9. What lies beneath the tectonic plates?
• Below the
lithosphere
(which makes
up the tectonic
plates) is the
asthenosphere.

10. Plate Movement
• “Plates” of lithosphere are moved around by
the underlying hot mantle convection cells

11. Practical Exercise 1
Supercontinents!

12. What happens at tectonic
plate boundaries?

13. • Divergent
• Convergent
• Transform
Three types of plate boundary

14. • Spreading ridges
– As plates move apart new material is erupted to
fill the gap
Divergent Boundaries

15. Age of Oceanic Crust
Courtesy of www.ngdc.noaa.gov

16. • Iceland has a divergent
plate boundary running
through its middle
Iceland: An example of continental rifting

17. • There are three styles of convergent
plate boundaries
– Continent-continent collision
– Continent-oceanic crust collision
– Ocean-ocean collision
Convergent Boundaries

18. • Forms mountains, e.g. European Alps, Himalayas
Continent-Continent Collision

19. Himalayas

20. • Called SUBDUCTION
Continent-Oceanic Crust Collision

21. • Oceanic lithosphere
subducts underneath the
continental lithosphere
• Oceanic lithosphere heats
and dehydrates as it
subsides
• The melt rises forming
volcanism
• E.g. The Andes
Subduction

22. • When two oceanic plates collide, one runs over the
other which causes it to sink into the mantle forming
a subduction zone.
• The subducting plate is bent downward to form a very
deep depression in the ocean floor called a trench.
• The worlds deepest parts of the ocean are found
along trenches.
– E.g. The Mariana Trench is 11 km deep!
Ocean-Ocean Plate Collision

24. • Where plates slide past each other
Transform Boundaries
Above: View of the San Andreas
transform fault

26. …what’s the connection?
Volcanoes and Plate
Tectonics…

27. Volcanism is
mostly
focused at
plate
margins
Pacific Ring of Fire

28. - Subduction - Rifting - Hotspots
Volcanoes are formed by:

29. Pacific Ring of Fire
Hotspot
volcanoes

30. • Hot mantle plumes breaching the
surface in the middle of a tectonic plate
What are Hotspot Volcanoes?
Photo: Tom Pfeiffer / www.volcanodiscovery.com
The Hawaiian island chain are
examples of hotspot volcanoes.

31. …what’s the connection?
Earthquakes and Plate
Tectonics…

32. • As with volcanoes, earthquakes are not
randomly distributed over the globe
• At the boundaries between plates, friction
causes them to stick together. When built up
energy causes them to break, earthquakes
occur.
Figure showing
the distribution of
earthquakes
around the globe

33. Plate Tectonics Summary
• The Earth is made up of 3 main layers (core,
mantle, crust)
• On the surface of the Earth are tectonic
plates that slowly move around the globe
• Plates are made of crust and upper mantle
(lithosphere)
• There are 2 types of plate
• There are 3 types of plate boundaries
• Volcanoes and Earthquakes are closely
linked to the margins of the tectonic plates

34. Ask the following Review questions:
- How are earthquakes distributed on the
map?
- Volcanoes and earthquakes are not
randomly distributed around the globe.
Instead, they tend to occur along limited
zones or belts. With the understanding of
plate tectonics, scientists recognized that
these belts occur along plate boundaries.

35. Where are they located?
The Pacific Ring of Fire includes these
Locations:
•New Zealand
•Southeast Asia (Eastern Portion)
•Northeast Asia (Eastern Portion)
•Russia
•Western Portion of North America incl
uding
Alaska to Mexico

36. • All of these volcanoes are located on th
e
"Pacific Side of those landforms." This g
eological arch gives birth to around 85% t
o 90% of the world's earthquakes and vol
canic eruptions. "Most of the Ring of Fire
Volcanoes" are
"Composite or Stratovolcanoes". That ca
n
contain thick silica rich lava

37. Where are places with no earthquakes?
- Is there any place in the world that
doesn't have earthquakes? Florida
and North Dakota are the states with
the fewest earthquakes. Antarctica
has the least earthquakes of any
continent, but small earthquakes can
occur anywhere in the World.

38. How are volcanoes distributed?
• (Ans: Volcanoes are not randomly
distributed. Majority of them are found
along the edges of some continents.

39. Where are they located?
• (Ans: Majority are found along the
edges of some continents, particularly
in the western coast of North and
South America, East and SouthEast
Asia.)

40. How will you relate the distribution
of mountain ranges with the
distribution of earthquake
epicenters and volcanoes?
(Ans: Mountain ranges are found in places
where volcanoes and/or earthquake
epicenters are also located.)

41. What do you think is the basis of scientists
in dividing Earth’s lithosphere into several
plates?
(Ans: Geologic activities such as
seismicity(occurrence of earthquake),
volcanism and mountain formation are the
basis of scientists in dividing Earth’s
lithosphere.

42. • Why do you think it is important
for us to identify areas which are
prone to earthquakes?
• If you are living near Canlaon
Volcano, what precautionary
measures would you do?