Earth layers, plates
Chapter 11
Inner core: solid
pressure from above layers.
temp 5500°C
Fe Ni
Outer core: liquid
Fe Ni
temp 5500°C
Mantle: largest layer
Si O Mg Fe
plastic like
acts as a solid but flows like a liquid when under pressure
ex. Silly putty or taffy
Crust: varies in thickness Thick – continental
crust - granite Thin – oceanic crust
– basalt
Crust is divided into sublayers
Lithosphere – crust and upper mantle - broken into 12 large plates that float on the mantle.Asthenosphere – plastic like layer below the lithosphereMohorovicic' discontinuity – boundary between crust and mantle.
Lithosphere
Continental Drift
Alfred Wegener –
1912 proposed theory of continental drift
continents have moved to their current locations
Theory of continental drift
One continent – Pangaea
200 m years ago
Panthalassa – one sea
Pangaea separated into
Laurasia
Gondwanaland
Separated by the Tethys Sea
Clues that support Continental Drift
Pieces of continents fit together like a jigsaw puzzleFossil clues – Mesosaurus(lived on land and in fresh water) - found in South American and
AfricaGlossopteris – found in Africa, Australia, India, South America and Antarctic - various climates - must have once been joined
Climate clues – fossils of warm plants found in the arcticGlacial deposits – grooved marks in bedrock found in SA, Africa, India, and Australia - must have been covered with glaciers at one time near south pole
Rock clues – If continents connected than rocks that make them up should be the same. - similar rock structures are found on different continents ex; Appalachian Mts similar to mountains in western Europe and Greenland
Wegener’s theory was laughed at even though he had evidence
After his death more evidence of how the continents were able to move were discovered to prove Wegener correct.
Mid-Atlantic Ridge
Longest mountain range on earth
Extends from Iceland along middle of Atlantic
Mid-Atlantic Ridge
Harry Hess
Discovered seafloor spreading
Evidence of Seafloor spreading
Rocks along rift areas were younger than those farther away. New lava rocks were being laid on either side of the rift
Magnetic reversals of the iron bearing basaltic rocks of the sea floor.
As the new rock was formed the iron particles in the rock aligned themselves with the magnetic poles of the earth at that time
Plate Tectonics
Earth’s crust and upper mantle are separated into plates.
Plates float on the mantle.
Make contact with each other.
Cause earthquakes and volcanoes, mountains
Composition of plates
Crust and upper mantle – lithosphere Less dense layer
floats on more dense layer
Asthenosphere – mantle More dense Plates flow on this
Plate Boundaries
Divergent Boundaries Move away from
each other mid-Atlantic Ridge Great Rift Valley in
eastern Africa
Great Rift Valley of Africa
Convergent PlatesPlates that come together.1. Ocean/continental
the ocean sinks below the continent.
remelts in mantleSubduction zone- where
ocean plate goes under continental plates
Volcanoes form here.Andes Mts.
2. Ocean/ocean One ocean plate
subducts under another and melts.
Forms deep sea trenches
Forms an island arc volcano
Japan
Oceanic-Oceanic Convergence
Island arcs – two ocean plates collide and one subducts to remelt lithosphere to cause volcanoes in the ocean floor.
Ex. Japan
Deep sea trench – forms where subducted plate melts into the mantle.
Ex. Mariana Trench
Pacific Ocean
3. Continental/
continental
- collision between plates cause the boundaries to crumble forming mountain ranges.
- earthquakes formed
- Himalayan Mts formed
Transform Fault Boundary Two plates slip past
one another Moving in opposite
directions Moving in same
direction at different rates
Earthquakes occur San Andreas Fault
Transform fault
Earthquakes formed
Causes of plate tectonics
Convection currents- Hot less dense
asthenosphere rises Cools – more dense
drops Reheats cycle
begins again
Effects of plate tectonics
Volcanoes
Earthquakes
Mountain building FAULT/BLOCK- Compression forces
fault causes weakness. Part of the land drops. Leaving behind higher ground.
Ex. Sierra Nevadas.
http://glencoe.mcgraw-hill.com/sites/dl/free/0078617006/164213/00038307.html
Folded mountains
Two plates collide with each other.
Ex. Appalachian Mts.
Anticline – upward fold in rocks
Syncline – downward fold in rocks.
Strike-slip Faults – plates moving past each other.
Snag onto each other storing up stress
Ex. San Andreas Fault
Strike slip fault
Rio Grand Rift
Rio Grand Rift
Found from Colorado, New Mexico and Texas
Hidden underground below sediment and basalt
Wrangell Mountains Alaska
Wrangell Mt. Alaska
Formed on floor of the Pacific ocean 9600 km from present location
Theory; they were scraped off ocean plate as it was subducted
Red Sea
Formed due to divergence along a triple junction of the Great Reft Valley in Africa and the Gulf of Aden.
Page 113 Critical thinking
Section: 3 page 289
1, 2, 3, 4,
Page 294
Vocab
Checking concepts
Thinking Critically 15,16, 17, 18, 20 23,24, 25