Plate Tectonics Chapter 7 page 214 Earth’s crust

Continental drift evidence 1-Coastlines seem to fit together like a puzzle
2-Sediment scratches in S America, Africa, and Australia suggest that glaciers once covered the land-similar climates
3-Plant and animal fossils have been found on several continents separated by oceans Pic p. 219
4-Common rocks and similar mountain chains that seem to connect on different continents<br>

What was missing? Not possible to measure due to how slow it happens
Couldn’t describe what forces caused the movement
The evidence was discovered decades later underneath the ocean water (on the sea floor)
Paleontologist continue to study fossils to prove Pangea<br>

7.2 Mapping the Ocean Floor 1940’s - scientist used echo location to map the ocean floor
Created topographic maps which showed mountain chains under the ocean water
Mid ocean ridges - mountain ranges under the ocean- longer than any mountain range on the land Pic p. 225<br>

Seafloor Spreading 1960’s Seafloor spreading - the process where new oceanic crust forms along a mid ocean ridge and older oceanic crust moves away from the ridge - was used to explain drifting
As seafloor spreads, less dense magma rises through cracks; as it cools rapidly, it forms basalt
New land is near the mid ocean ridge but old land drifts further away<br>

Topography of Seafloor Proof Mid ocean ridges form 2 ways: 1)Lava erupts from the seafloor; cools and builds up around the ridge 2) Lava cools to form new crust then cracks causing rocks to move up or down forming jagged mountain range
Sediment is deposited on top of oceanic crust; as the weight of sediment increases, the pressure creates the abyssal plain. Sediment can be dated also.
*Continents move as the seafloor spreads along this ridge.<br>

Earth’s Magnetic Field Rocks record magnetic information due to iron in core of the Earth-creates our magnetic field. Direction of field is not constant. Sometimes it reverses.
Normal polarity-compasses point north; Reversal polarity-compasses point south<br>

More Evidence Basalt on the seafloor contains minerals that act as magnets.
When magma under the ocean cools and crystallizes, it records the direction of Earth’s magnetic field Pic p. 228
Scientists have discovered parallel patterns in rocks on both sides of the mid ocean ridge with similar composition and age.
Drilling in seafloor finds more thermal heat near mid ocean ridge.<br>

7.3 Plate Tectonics Plate tectonics states that Earth’s surface is made of rigid rock (plates) that move
Geologist have suggest that Earth’s crust is divided into large plates that move over Earth’s hot semi plastic mantle (think of Laffy Taffy)
Google map of Earth’s tectonic plates on p. 234<br>

Earthquakes & Volcanoes EQ of mid ocean ridge-when plates separate on seafloor or when plates slide past each other
When tectonic plates come together, one plate can dive under the other causing earthquakes and creating a chain of volcanoes
Ring of Fire-area in Pacific Ocean where many earthquakes & volcanoes erupt annually Pic p. 237
AMSTI Activity<br>

Tectonic Plates p. 234 Pacific plate is the largest; Jan de Fuca is the smallest
Borders that run through the ocean are mid ocean ridges
Lithosphere is the outermost rock layer of Earth (crust) and is cold and hard large plates.
Asthenosphere is the next layer below the lithosphere-it is so hot that it is gooey causes the plates to flow<br>

Plate Boundaries p. 236 1)Divergent-separating plates destroy land-form mid ocean ridges in water and valleys on land Ex: East African Rift
2)Convergent-colliding oceanic plates form subduction zones/trenches: Oceanic crust submerges under continental crust and volcanoes form above this area. Ex: Mariana Trench Colliding continental plates create land- form mountains Ex: Himalayas
3)Transform-sliding plates do not create or destroy land Ex: San Andreas Fault in California<br>

GPS GPS is determined by a 4 satellites in space (12,550 miles high)-each satellite circles Earth twice daily and lasts about 10 years if they are constantly updated Ex: Google Earth
There are 4857 satellites in space and 685 belong to U.S. (not all are GPS)
Global Positioning System can also measure the distance between satellites and plates to determine how fast continents move - which is a few centimeters per year<br>

Plate Motion Proof Warm air rises while cold air sinks. Convection current is the circulation of air based on differences in temperature.
Materials in Earth’s mantle increase and decrease in heat creating convection currents-acting as a conveyor belt in Earth’s lithosphere Pic p. 239
Three forces cause plate motion: basal drag, ridge push, and slab pull<br>

Show Off Day- TEST Time :) Study main ideas on p. 244
Complete and study review on p. 245-247
Know vocabulary
Quizlet
A+ coming your way! :)<br>