its about earth quake Some plates have continents; some don't. All are in motion. Question: What evidence is there for these plate boundaries? Tectonic Plates ...

1. New Zealand Earthquake
• M 6.3 earthquake
• Shallow epicenter: 2-
3 miles
• Close to Christchurch,
city of 370,000
• After shock to the
September 4th M 7.1

2. What is the composition of
lava formed on oceanic crust?
High percentages Fe, Mg
Low percentages Si, O

3. DESCRIBE A CONVERGENT
PLATE BOUNDARY

4. What is the source of the lava
that forms oceanic crust?
the mantle or asthenosphere

5. What is the composition of
lava associated with
continental crust?
High percentages Si, O
Low percentages Fe, Mg

6. The Theory of Plate Tectonics
• Based on two hypotheses
– Continental Drift
– Seafloor spreading

7. Explain the development of the
theory of plate tectonics in
terms of the scientific method.

8. The
Scientific
Method
One or more ideas, statements or questions;
Single or multiple hypotheses
Collection of data
Observation of data or information
Theory
Not accepted Hypothesis
More Data

9. Continental drift hypothesis:
evidence?
• Proposed in 1911
• All evidence found on the continents
• Mechanism for moving the continents was
not known

10. • Alfred Wegener
proposed the
hypothesis of
continental drift in
1911
• He gathered
information from many
different sources and
used it as evidence for
his hypothesis
Continental Drift Hypothesis

11. • Fit of the continents
• Fossil evidence
• Ancient mountain ranges
• Past climate evidence
Continental Drift Hypothesis
Glaciers formed at the south pole
Swamps formed in tropical regions

12. • The
continental
drift
hypothesis
proposes that
the continents
were
assembled to
form the super
continent
Pangaea.
• Moved
through time
3:20

13. • Antonio Snider-Pelligrini
(1858), a geographer cut
out a map of Africa and
South America
suggesting they were
connected at one time
• Other physical evidence
based on observation
was used by Wegener
Fit of Continents

14. Fossil Evidence
• Similar terrestrial species were found on many
continents now separated by oceans.
• Information collected by paleontologists

15. Ancient Mountain Ranges
The same sequence of rocks is found in North America,
Great Brittan, and Norway. The pattern does not make
sense with the continents in their current configuration.

16. The Appalachian Mountains
Swamps
300 million years ago

17. Evidence of
Ancient Glaciers
•Glaciers carve the rock as they move.
•Scientists can determine the direction of movement (notice the
direction of movement noted in South America)
•As South America sits today, the pattern would not make sense.
(glaciers do not move from sea level to higher elevations)

18. Lack of mechanism to explain
continental movement.
• Evidence implied that the continents were at one
time assembled
• Wegener’s idea was not accepted by the
scientific community because he could not
explain how the continents moved
• With advances in technology, new information
was gathered in association with WWII

19. • What information do you know regarding
the seafloor that may be used to help
understand the hypothesis of seafloor
spreading?
Exploration of the Ocean Basins

20. Exploration of the Ocean Basins
• Seafloor features
• Composition of the seafloor
• Age of the seafloor
• Hot spots
• Seismicity
• Paleomagnetic pattern produced on the
seafloor

21. Exploration of Ocean Basins
Ocean basins contain a variety of landforms not discovered until WW II.

22. Support
• Echo sounding was used to map the seafloor
Seafloor features were
discovered using sonar.
4:26

23. Seafloor
features
• Mid-oceanic
ridges
• Trenches
• Volcanism
adjacent to
trenches
• Seamounts
• Fracture zones

24. Oceanic crust is composed of
volcanic rock.
• Basalt is volcanic rock with a mafic composition.
• Higher percentages of iron and magnesium, lower
percentages of silicon and oxygen.
Pillow basalts

25. Age of Ocean Crust
• Youngest at ridge
• Progressively older away from ridge
• Mirror image across the ridge

27. Seismicity
• Earthquakes are concentrated at what is
currently known as plate boundaries.
• Explain why there are broad bands of
seismicity associated with some areas.

29. Earth’s Magnetic Field
Bipolar:
acts like
a bar
magnet

32. Requirements for a magnetic
field
• An interior region of electrically conducting
fluid such as molten metal.
• Convection in that layer of fluid.
• At least moderately rapid rotation.

33. A compass has a different
declination depending on the
location on the Earth’s surface

34. Earth’s Magnetic Field
• Strength varies with location
– Red- stronger
– Blue weaker

35. Iron-rich rocks are magnetized as
they cool to the current magnetic
field.
• Basalt= iron rich volcanic rock; oceanic
crust

36. Paleomagnetic pattern across the
mid-oceanic ridge
Mirror image across the ridge and correlative with age
Positive
anomalies=
normal
polarities
Negative
anomalies =
reverse
polarities

37. Polar
Reversals
• Correlated to time
• Scientists dated iron-
rich volcanic rocks on
land
• Developed
technology to
measure the
paleomagnetic
reading

38. Polar Reversals
• Timescale of polar
reversals
• Possibly related to
flow in the outer
core

39. Paleomagnetic Evidence
• Positive and negative recordings of the
oceanic crust create a symmetrical pattern
across the mid-oceanic trench

40. • In the 1963, Harry
Hess developed the
idea of seafloor
spreading to explain
the seafloor’s
formation
• Continental
movement is the
result of ocean floor
movement
Seafloor Spreading

41. Seafloor Spreading
• Mafic lava is extruded along the mid-oceanic ridge to
produce ocean floor.
• New material is added, the cooler material is split and is
“pushed” away from the ridge

42. Driving Mechanisms
Convection cells within
the mantle
Pushing at the mid-
oceanic ridges
Pulling at the subduction
zones
Push
Pull
Convection

43. The theory of plate tectonics
• Explains that the Earth’s lithosphere is
broken into distinct units that move as a
coherent package. Where the tectonic
plates meet, produces distinct physical
characteristics on the Earth’s surface.

44. The Scientific Method
Continental Drift Hypothesis
Collection of data
Observation of data or information
Theory of Plate Tectonics
Mechanism for plate movement
Not accepted
Seafloor Spreading Hypothesis
Associated
with the
continents
Ocean
basins
key

45. Information to understand:
• The evidence used by Wegener to describe
the continental drift hypothesis.
• The evidence associated with technology that
was used to collect information about ocean
basins.
• The hypothesis of seafloor spreading
• The accepted tectonic plate driving
mechanism.

46. Earthquakes and volcanoes outline
the tectonic plate boundaries