A

1. GOOD DAY
GRADE 10

2. PLATE
TECTONICS

3. PLATE
TECTONICS
• The theory that the Earth’s outermost layer
is fragmented into a dozen or more large
and small plates that move relative to one
another as they ride on top of hotter, more
mobile material.

4. PLATE TECTONIC
• 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.

5. • At the beginning of the 20th century,
many scientists explained the physical
attributes of the Earth using the Raisin
Theory.

6. WHAT IS THE RAISIN
THEORY?
• known as the "Geosynclinical
Theory" or "Geosyncline
Hypothesis",
• According to this principle, the
level of the Earth’s crust is
determined by its density; lighter
material rises, forming continents,
mountains, and plateaus, and
heavier material sinks, forming
basins and ocean floors.
Clarence Edward
Dutton

8. Convection is like a boiling pot. Heated soup rises to the surface, spreads and begins to
cool, and then sinks back to the bottom of the pot where it is reheated and rises again.
Plate tectonics
• Plates are driven by cooling of Earth (convection)
• Gravity provides additional force to move plates.
Modified from USGS Graphics
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9. What are the tectonic plates?
AKA: Lithospheric plate
• The ~100-km-thick surface of the Earth;
• Contains crust and part of the upper mantle;
• It is rigid and brittle;
• Fractures to produce earthquakes.

10. What is the asthenosphere?
Asthenosphere:
• Is the hotter upper mantle below the lithospheric
plate;
• Can flow like silly putty; and
• Is a viscoelastic solid, NOT liquid!!
USGS
Graphics

11. Three Basic Types of Plate Boundaries
Divergent
Convergent
Transform
USGS Graphics
Using hands to show relative motion

12. Three Basic Types of Plate Boundaries
Divergent
Convergent
Transform
USGS Graphics

13. There are a dozen large lithospheric plates (smaller plates not shown).
Some plates have continents; some don’t. All are in motion.
Question: What evidence is there for these plate boundaries?
Tectonic Plates

14. There are thousands of small earthquakes every day
“Strong” earthquakes (~M7) occur once a month. >M8 occur about once/year.
Earthquakes
Where are the deepest earthquakes?
For earthquakes of the past 2 weeks, go to http://www.iris.edu/seismon/

15. Notice that the earthquakes coincide with plate boundaries,
and the deepest quakes (blue) are in subduction zones.
Question: Where would you expect to see volcanoes?
Modified from USGS Graphics
Earthquakes & Plate Boundaries
Create your own maps at http://www.iris.edu/quakes/maps.htm

16. Modified from USGS Graphics
This map shows that locations of volcanoes (ones above sea
level) also tend to occur along the plate boundaries
Volcanoes & Plate Boundaries

17. How fast are the plates moving?
Plates move 1-10 centimeters per year (≈ rate of fingernail growth).
Tectonic Plates
Modified from USGS Graphics
Fingernail growth plotted: http://jclahr.com/science/earth_science/thumbnail/index.html

18. How fast are the plates moving?
Plates move 1-10 centimeters per year (≈ rate of fingernail growth).
Continental Drift
Source: http://www.tectonics.caltech.edu/outreach/animations/index.html

19. •CONTINENTAL DRIFT
•Alfred Wegner was one of several people who thought the
continents looked like they fit together, so he proposed the
continental drift theory in 1912.
Wegner was a meteorologist and astronomer so needless
to say other scientists thought he was out of his field of study.

20. •His studies concluded that at one time all the continents were
joined together in one land mass called Pangaea.
• 1. Laurasia was the name given to the northern part of
Pangaea
•2. Gondwanaland was the name given to the southern
part of Pangaea

21. Scientists thought this
theory was outrageous
because even though
Wegner had evidence of
one large land mass, he
didn’t have the answers to
what force (engine)
“floated the plates”. He
was laughed at and did not
live to see his theory
accepted.
•This animation begins with the
continents in their present location,
and then moving back in time to
form PANGAEA. The circles
represent fossil evidence that
Wegner used to prove his
Continental Drift Theory.
•PANGAEA means “all land”

22. • WHERE’S THE EVIDENCE
• Wegner had 5 pieces of evidence to prove his continental
drift theory:
1. PUZZLE PIECES:
• The continents, especially South America and Africa,
seemed to fit together like a puzzle.

23. 2. FOSSIL EVIDENCE:
• Wegner noticed that plant and animal fossils were found on
different continents.
 Do you think they swam all the way across the oceans?
NO!
 This would lead people to believe that the continents were
once joined.
•Glossopteris…seed much
to large to be windblown
•Mesosaurus…lived in fresh
water and could not have
lived in salt water

25. •3. ROCK EVIDENCE:
•Huge belts of rocks found in
Africa and South America
were identical. Not only were
they the same, but they would
match up (age, thickness,
types) if the continents were
put together.
•Matching Mountains
•The Appalachian
Mountains that disappear off
the coast of Newfoundland
match mountains in the
British Isles and Scandinavia
which are comparable in age
and structure.

26. •4. GLACIER EVIDENCE:
•There is proof that glaciers moved from Africa, through the
Atlantic Ocean, and then on towards South America. This
would be much easier if the Atlantic Ocean were not there

27. •Glacial Striations…Scratches glaciers leave
•on rocks as they travel

28. •5. CLIMATE EVIDENCE:
•Warm weather plants have been found in the Arctic…
but it’s not warm there!
•Glacier deposits have been discovered in tropical and
desert locations…it’s not cold there, either!
•The continents had to have been at different locations in
the geological past.
•DVD on Continental Drift

29. •?????????? ONE QUESTION REMAINED ??????????
•WHAT FORCE WAS MAKING THE CONTINENTS MOVE
•TOMORROW
•FIND OUT
•WHAT FINALLY PROVED THAT WEGNER’S
•CONTINENTAL DRIFT THEORY
•WAS RIGHT?

30. • AMAZING EARTH SCIENCE FACTS
1. The 4 pieces of evidence that support
Continental Drift are
•______________ fit together like puzzle pieces
•__________ showing the same types of life existed
•on the now separated land masses
•___________________________match up along
•coastlines of once joined continents
•____________ evidence in temperate and hot
•climates
•Continents
•Fossils
•Rock layers & mountains
•Glacial

31. Seafloor Spreading
Source: http://www.tectonics.caltech.edu/outreach/animations/index.html

32. Collision of ‘Drifting’ India with Eurasia
Source: http://www.tectonics.caltech.edu/outreach/animations/index.html
Side view of subduction, ‘drifting’ India, volcanoes, & mountain-building

33. Note on Source: First 8 slides are modified from a slide show prepared by Dr. Robert
Butler, University of Portland, and Jenda Johnson,
…the full source of which can be found at:
http://www.iris.edu/hq/programs/education_and_outreach/videos#B