Plate Tectonics Study Guide
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Plate Tectonics Study Guide
Earth’s Structure
1) List and describe the Earth’s Compositional layers.
a) Crust – outermost layer, thinnest layer, 2 kinds: continental (least dense high silca) oceanic (more dense low silica, high metal content)
b) Mantle- slow moving solid rock located between the crust & the core. Mantle is more dense than the crust and contains more magnesium and less aluminum than the crust
c) Core-center of the Earth made of mostly iron and nickel
2) List and describe the Earth’s physical layers.
a) Lithosphere- rigid outer layer of the Earth. Includes the crust and the uppermost part of the mantle
b) Asthenosphere- layer of weak or soft rock that flows slowly, convection currents flow, lithosphere floats on top of it
c) Mesosphere- Strong solid part of the mantle that flows extremely slowly
d) Outer Core- liquid iron, it rotates at a different rate than the inner core causing the Earth’s magnetism
e) Inner core- solid dense core of solid iron
3) What happens to heat and pressure as you go deeper into the Earth? They both increase.
4) In which physical layer do scientists think that convection currents flow? Asthenosphere
5) What evidence is used to infer what the interior of Earth is like? Earthquake waves are used to get a picture of the interior of the Earth, much like ultrasound waves give a picture of a baby in utero.
Continental drift & Sea Floor Spreading
6) List and describe the 3 forms of evidence Wegener used to support Continental Drift?
a) Land forms- The continents fit together like a puzzle, where the pieces connect, the landforms also match. Mountains with mountains, coal fields with coal fields.
b) Fossils- extinct animals are found on different continents with no way to cross the oceans, this is evidence that the continents were connected while those species were alive.
c) Climate- artic islands have fossils of tropical plants, which shows they were closer to the equator and drifted north, glacier deposits in Africa indicate that it was located close to the south pole and has drifted towards the equator.
7) Why did most geologists reject the idea of Continental Drift in Wegener’s time? He could not describe a credible mechanism for how the continents moved.
8) Describe what sea floor spreading is: It occurs when molten material erupts at the mid-ocean ridge, pushing older crust away from the ridge to eventually be consumed by subduction at an ocean trench. This is the mechanism that Wegner needed to prove his hypothesis.
9) List and describe the 3 forms of evidence for sea floor spreading.
a) Molten material- molten material was observed erupting at the mid-ocean ridge and formed “pillow lava”. The pillow lava I found across the ocean floor far away from where it forms. This shows that the crust itself is moving and taking the rocks with it like a conveyor belt.
b) Magnetic stripes- the rocks forming the ocean floor are rich in iron, when they form the direction of magnetism is permanently stored in the rocks. The pattern of magnetism is in alternating stripes. This means that the ocean floor is constantly changing and could not have been made in a single event or that the Earth’s surface is unchanging.
c) Drilling samples- samples show that the youngest rock is close to the mid-ocean ridge, and the older crust is further away from the ridge.
10) How did scientists map the ocean floor? With sonar
11) Describe subduction: is when a more dense oceanic plate is forced under a less dense plate where it is recycled and melted back into the mantle
12) Describe the 3 types of plate boundaries and the geologic features that form there:
a) Transform: When 2 plates slide past each other in opposite directions. When the plates lock, the pressure build until the rocks fail causing an earthquake.
b) Divergent: When 2 plates move away from each other.
i) Continental: rift valley forms, eventually will become sea floor spreading.
ii) Oceanic: Mid-ocean ridge forms with sea floor spreading.
c) Convergent: When 2 plates collide moving towards each other.
i) Cont/cont: Folded mountains form
ii) Cont/oceanic: Subduction of oceanic crust causing a deep ocean trench and a volcanic mountain range on the continent.
iii) Oceanic/oceanic: Subduction of oceanic crust causing a deep ocean trench and a volcanic island arc in the ocean.
d) Describe the processes that cause Plate Tectonics to occur:
i) Convection: As convection currents flow in the asthenosphere they drag on the Earth’s lithospheric plates causing them to move.
ii) Ridge push: As molten crust erupts at the mid-ocean ridge it pushes older crust away from the ridge, that crust gets more dense as it cools, gravity then pulls harder on the crust widening the ridge.
iii) Slab pull: As the more dense plate is subducted, it starts getting sucked down by the asthenosphere, because its density is greater than the mantles hot semi-solid material.