Transcript Plate Tectonics - Londonderry School District

Theory of Plate Tectonics
1. Continental Drift Theory
• Alfred Wegener
• German meteorologist
• Found papers describing
similar fossils on opposite
sides of the Atlantic
• Researched more cases of
similar organisms
separated by oceans
• 1912 Proposed single
supercontinent Pangaea
2. Continental Drift Theory
5 Types of Evidence
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Fit of the Continents
Distribution of Fossils
Sequence of Rocks
Glacier Scraping Patterns
Ancient Climates and
Wandering Polar Regions
http://library.thinkquest.org/3669/media/map2dd.GIF
3. Wegener’s Continental Drift Evidence:
• Continents ‘fit’
together in a single
land mass 250 mya
• CLICK Simulations
http://www.ucmp.berkel
ey.edu/geology/anim1.
html
http://www.eoearth.org/upload/thumb/f/fb/Plate_tectonics_over_time.gif/400px-Plate_tectonics_over_time.gif
4. Wegener’s Continental Drift Evidence: Plant and
animal fossils of the same species were found on
several different continents.
5. Wegener’s Continental Drift
Evidence:
Similar sequence of rock or
rock formations have the same age
6.Wegener’s Continental Drift Evidence: Glacial
deposits, striations,
and scraping patterns
7. Wegener’s Continental Drift Evidence: Climate
distribution
Past
Present
Coal exists under the ice in the rock of Antarctica –
yet coal can only form from plants that grow in warm climates.
8. Wegener’s Theory Problems
1) Wegener had no convincing mechanism
(did not explain the forces) of how the
continents might move. Continents plowing
through the crust would destroy the crust.
2) Continents are not moving apart at the
speed Wegener proposed.
Wegener = 250cm/yr
Actual = 2 cm/yr
9. Holme’s theory:
Heat trapped in the Earth caused convection currents in the
mantle. Breakthrough theory that changed all thought on
what was happening inside the Earth.
• As a substance is heated its density decreases
and rises to the surface until it is cooled and
sinks again.
10. Convection Currents
• Gravity causes the
heated mantle to sink
• The mantle heats up near
the core and then rises
again
• Conduction is the transfer
of heat between 2
materials in direct contact
with each other
library.thinkquest.org/C003124/images/convect.jpg
http://www.wisc-online.com/objects/index_tj.asp?objID=SCE304
Click animation
11.New Evidence: Magnetic pattern of rock
Volcanic rocks on the seafloor have
magnetization because, as they cool,
magnetic minerals within the rock align to
the Earth’s magnetic field.
12.North Magnetic Pole in No.
Hemisphere
13.North Magnetic Pole in So. Hemisphere
14. Present Day
North Magnetic Pole in No.
Hemisphere
15. Sea-Floor Spreading Hypothesis
by Hess & Deitz
In the late 1950's, scientists mapped the present-day magnetic field generated by rocks on the floor of
the Pacific Ocean. The volcanic rocks which make up the sea floor have magnetization because, as
they cool, magnetic minerals within the rock align to the Earth's magnetic field. The intensity of the
magnetic field they measured was very different from the intensity they had calculated. Thus, the
scientists detected magnetic anomalies, or differences in the magnetic field from place to place. They
found positive and negative magnetic anomalies. Positive magnetic anomalies are places where the
magnetic field is stronger than expected. Positive magnetic anomalies are induced when the rock
cools and solidifies with the Earth's north magnetic pole in the northern geographic hemisphere. The
Earth's magnetic field is enhanced by the magnetic field of the rock. Negative magnetic anomalies are
magnetic anomalies that are weaker than expected. Negative magnetic anomalies are induced when
the rock cools and solidifies with the Earth's north magnetic pole in the southern geographic
hemisphere. The resultant magnetic field is less than expected because the Earth's magnetic field is
reduced by the magnetic field of the rock.
16. Sea Floor Spreading simulation
CLICK Animation:
http://www.uwsp.edu/geo/faculty/ritter/gloss
ary/s_u/sea_flr_spread.html
17. Plate Tectonics Theory
www.wiley.com/college/herenow/ptect/pt-map1.gif
Theory that Earth’s crust and rigid upper mantle (Lithosphere) moves
Lithosphere is broken into slabs or plates that move independently
from one another. Plates ‘float’ on the Asthenosphere
Plates have oceanic and continental crust.
18. Earth’s Layers
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http://library.thinkquest.org/04oct/01724/images/Earth-crust-cutaway-english.png
Inner Core
Outer Core
Mantle
Crust
Atmosphere
• Lithosphere – crust and
upper mantle, plates
move independently
• Asthenosphere-region
below the Lithosphere
19. Continental Crust
http://www.amonline.net.au/geoscience/images/earth_diagrams/cont_oceanic_crust.gif
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Cooling rate - slow
Crystal size - large
Density – less dense
Thickest portion of the Earth’s outer layer (20-30 miles thick.
Composition – made mainly of granite rock
20. Oceanic Crust
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Cooling rate - fast
Crystal size - small
Density – more dense
Thinnest portion of the Earth’s outer layer
Composition – Made mainly of basalt rock
http://faculty.weber.edu/bdattilo/parks/plume_ocean.jpg
21.Volcano - opening or rupture in the Earth’s
crust that allows molten rock to escape
http://cgz.e2bn.net/e2bn/leas/c99/schools/cgz/accounts/staff/rchambers/GeoBytes%20GCSE%20Bl
og%20Resources/Images/Plate%20Tectonics/Plate%20Tectonics/VolcanoStructure.jpg
22. Earthquake - result of sudden energy release
in the Earth’s crust creating seismic waves.
•
http://news.bbc.co.uk/nol/shared/spl/hi/world/04/earthquake/img/earthquake.gif
23. More Evidence: Location of mountain ridges,
rift valleys, mid-ocean ridges, and trenches on
plate boundaries.
Convergent, Divergent and Transform
http://www.ifa.hawaii.edu/~barnes/ast110_06/tprai/Tectonic_plate_boundaries.png
SIMULATIONS ON ALL BOUNDARY TYPES
CLICK http://www.pbs.org/wgbh/aso/tryit/tectonics/shockwave.html
There are 3 types of
Plate Boundaries
• Divergent Boundary
• Convergent Boundary
• Transform Boundary
24. Convergent Oceanic & Continental
Andes Mountains
Plates move toward each other. Denser oceanic crust
subducts under less dense continental crust.
A trench, a steep walled valley on the sea floor, forms here.
blue.utb.edu/paullgj/images/Conv_Cont_Ocean.JPG
CLICK
http://www.pbs.org/wgbh/aso/tryit/tectonics/convergent.html
25. Convergent Boundary
Oceanic & Continental
CLICK http://geology.com/nsta/convergent-boundary-oceanic-continental.gif
26. Japan or Aleutian Islands
Convergent Oceanic & Oceanic
Denser oceanic crust subducts under less dense oceanic crust
ceeps.colostate-pueblo.edu/.../smM1P1Fig15.gif
27. Convergent Boundary
Oceanic & Oceanic
http://geology.com/nsta/convergent-boundary-oceanic-oceanic.gif
28. Convergent Continental & Continental:
Himalayas
Faulting and Folding
http://www.pbs.org/wgbh/aso/tryit/tectonics/crush.html
29. Convergent Boundary
Continental & Continental
http://geology.com/nsta/convergent-boundary.gif
30. Mid Atlantic Ridge
Divergent Oceanic
At a divergent boundary
lithosphere plates move
away from each other
Example: Mid-Atlantic
Ridge- North American
Plate and Eurasian Plate
are moving away from
each other
31. Divergent Boundary - Oceanic
• Mid-Ocean Ridges – a structure formed from
seafloor spreading. Same as slide # 30
CLICK http://geology.com/nsta/divergent-boundary-oceanic.gif
32. East African Rift Valley
Divergent -Continental
Rift Valley – Pulling apart of continental crust due to
tensional forces
ceeps.colostate-pueblo.edu/.../smM1P1Fig15.gif
33. Divergent Boundary
Continental
• Rift Valley
http://geology.com/nsta/divergent-boundary-continental.gif
34. Transform Plate Boundary
Plates slide past each other
Ex: San Andreas Fault
www.wiley.com/college/herenow/ptect/pt-map1.gif
35. Transform Boundary
TRANSFORM SIMUALTIONS
CLICK http://geology.com/nsta/transform-boundary.gif
CLICK http://www.pbs.org/wgbh/aso/tryit/tectonics/transform.htm
36. Evidence - Location of earthquakes and volcanoes
http://vulcan.wr.usgs.gov/Imgs/Gif/PlateTectonics/Maps/map_plate_tectonics_world.gif
37. Ring of Fire
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A dramatic example is the line of volcanoes that circles most of the Pacific Ocean.
This belt is known as the "Ring of Fire" because it is the site of frequent volcanic
eruptions. Volcanoes are also distributed in long belts that circle the Earth.
The distribution of earthquakes and volcanoes coincides at most locations. The Ring
of Fire is an excellent example. Geologists believe that areas of intense geologic
activity, indicated by earthquakes, volcanoes, and/or mountain building, mark the
boundaries between lithospheric plates. The distribution of earthquakes, volcanoes,
and mountain ranges define 7 large plates and 20 smaller plates. The Nazca and
Juan de Fuca Plates consist of only oceanic lithosphere. The Pacific Plate is mostly
oceanic lithosphere only a small slice of continental lithosphere in southern California
and Baja Mexico. Most of the other plates consist of both oceanic and continental
lithosphere.
38. Hot Spots – hot narrow plumes of magma
that rise upr from the mantle and heat/melt an area
of crust
39.The Hawaiian-Emperor volcanic chain
is the result of the drifting of the Pacific
Plate over a fixed hot spot.
http://geology.com/nsta/plate-tectonics-cover.gif
40. The bend in the (Hawaiian – Emperor)
volcanic chain is the result of a major change in the
direction of the movement of the Pacific Plate.
41. Location of Hot Spots
Hot spots result from hot, narrow plumes of
material that rise deep within the mantle.
42. Plate Movement in the future
• http://www.scotese.com/earth.htm
It is even possible to measure the speed of continental
plates extremely accurately, using satellite technology.
43. External Energy For Earth
• Sun & Moon keeps air and sea in motion,
shapes surface
• Sun warms atmosphere & crust unevenly
creating winds
• Winds drive ocean currents and water cycle
• Erosion from winds, rains, rivers, glaciers, and
waves shape surface
• Weathering from winds and rains
• Sun & Moon Gravitational Energy, produces
tides
• Planetesimal collisions
44. Internal Energy for Earth
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Radioactive element decay
Core heat from layers pressure
Convection currents
Volcanoes
Hot Springs
Earthquakes