Plate Tectonics Flashcards
The theory that explains many of Earth’s geologic features by saying that the crust is broken into moving pieces.
Plate Tectonics
A piece of Earth’s crust that can move.
Plate
The outer layer of the Earth.
Crust
The layer below the crust.
Mantle
The deepest layer of the Earth.
Inner Core
The layer below the mantle.
Outer Core
Describe the changes in temperature within the Earth.
The temperature gets hotter and hotter with the deeper layers - so the inner core is the hottest.
Describe the changes in density within the Earth.
The density increases with the deeper layers - so the crust is the least dense, and the inner core is the most dense.
Describe the state of each layer within the Earth.
Crust = solid
Mantle = liquid
Outer Core = liquid
Inner Core = solid
Describe the composition of each layer within the Earth.
Crust = solid rock
Mantle = molten rock
Outer core = molten metal
Inner core = solid metal
How did scientists discover the layers with the Earth?
They measured the ways that earthquake waves change when they pass through the different layers.
What force is powerful enough to move the plates?
Convection currents in the mantle.
Which layer includes both the crust and the upper mantle?
Lithosphere
The lower part of the mantle is called the…
Asthenosphere
Which layer of the Earth makes up the plates?
Lithosphere
Which layer of the Earth has convection currents that move the plates?
Asthenosphere
How heavy something is.
Mass
The amount of gravity pulling on an object.
Weight
The amount of space filled by an object.
Volume
How heavy an object is, compared to its size.
Density
The mathematical formula for finding density.
Density = Mass divided by Volume ( D = M / V )
The density of an object that sinks.
Greater than 1.0
The density of an object that floats.
Less than 1.0
A. Find the density of an object that has a mass of 8 g and a volume of 2 ml.
B. Then tell whether it will sink of float.
A. 8 / 2 = 4
B. It will sink
A. Find the density of an object that has a mass of 20 g and a volume of 40 ml.
B. Then tell whether it will sink or float.
A. 20 / 40 = 0.5
B. It will float
What will happen when hot and cold water mix? Why?
The hot water will float on top of the cold water, because the hot water has a lower density.
What will happen when freshwater and saltwater mix? Why?
The freshwater will float on top of the saltwater, because the saltwater has a higher density.
Explain HOW convection currents happen.
- Warm liquids have a low density, so they float upward.
- The liquid at the top spreads out to the sides.
- The liquid at the top cools down and sinks.
- The liquid at the bottom gets heated up again, and the cycle starts over.
What is the source of heat in the Earth that creates the convection currents in the mantle
Radioactivity
Are plates the same as continents? Explain.
No - plates include continents as well as the ocean floor.
Name the two types of crust.
Oceanic crust and continental crust.
Compare the thickness of the two types of crust.
Oceanic crust is thinner than continental crust.
What kind of rocks make up the two types of crust?
Continental crust is made of granite, oceanic crust is made of basalt.
Compare the density of the two types of crust.
Continental crust is less dense than oceanic crust.
Compare the ages of the two types of crust.
Continental crust is much older than oceanic crust.
What features of the Earth are found near plate boundaries?
Volcanos, earthquakes, mountain ranges, deep-sea trenches, rift valleys, and more.
Name the boundary where plates move apart.
Diverging Boundary
Name the boundary where plates move together.
Converging Boundary
Name the boundary where plates slide past each other.
Transform Boundary
List features found at a diverging boundary.
Mid-ocean ridge, rift valley
What process occurs at a diverging boundary?
Sea-floor spreading
How is a mid-ocean ridge formed?
The edges of the plates are lifted by rising magma.
How is a rift valley formed?
The crust is split apart when the convection currents drag the plates in opposite directions.
Describe sea-floor spreading.
The ocean grows wider and wider as new crust is created at the rift valley.
Compare the ages of rocks close and far from the mid-ocean ridge.
Rocks close to the mid-ocean ridge are younger than rocks far from the ridge.
Compare the thickness of the sediments close and far from the mid-ocean ridge.
There is a thin layer of sediments near the ridge, and the sediments get thicker farther away.
Give an example of a diverging boundary.
The Mid-Atlantic Ridge
List the features found where a continent collides with another continent at a converging boundary.
A folded mountain range, earthquakes, and folded rocks.
Describe what happens when one continent crashes into another continent.
The land crumples up to make a folded mountain range. This also folds the rocks and causes earthquakes.
Give an example of a place where one continent crashed into another continent.
India crashed into Asia, which formed the Himalayas.
List the features found along a transform boundary.
Earthquakes and faults.
Explain how plate movements along a transform boundary cause earthquakes.
The rough edges of the plates grind against each other, and sometimes they get stuck. When the force breaks them free, it makes an earthquake.
List the features found where continental crust crashes into oceanic crust at a converging boundary.
Subduction zone, volcanos, deep-sea trench, earthquakes.
The location where oceanic crust is pushed underneath another piece of crust.
Subduction zone
Explain why oceanic crust slides underneath continental crust at a subduction zone.
The oceanic crust is more dense, so it gets pushed down underneath the continental crust.
Explain how volcanos are formed at a converging boundary.
When the oceanic crust is pushed underneath the continent, it heats up and melts. The new magma rises through the upper plate, and erupts as a volcano at the surface
Explain how deep-sea trenches are made.
The oceanic crust gets pulled downward when the plate is subducted underneath another plate.
The process where one plate is pushed underneath another, and it gets carried deep into the mantle.
Subduction
Give examples of volcanos formed at converging boundaries.
Mt. St. Helens (part of the Cascades), the Andes, the Japanese islands, the Aleutian islands, Indonesia, and the Phillipines (PS - all of these are part of the Ring of Fire!)
Give an example of a deep-sea trench.
The Marianas Trench in the Pacific Ocean.
About how fast do plates move?
A few centimeters a year (about the speed that your fingernails grow).
A series of volcanoes that surround the Pacific Ocean.
The Ring of Fire
Give an example of a place where a transform boundary causes many earthquakes.
The San Andreas fault, where the Pacific plate slides past the North American plate.
Why are the Hawaiian volcanoes different than most other volcanoes?
The Hawaiian volcanoes are not on the edge of a plate.
How does the theory of plate tectonics explain the formation of the Hawaiian volcanos?
Each island was formed one at a time as the Pacific plate moved over a hot spot. When the plate moved, it carried the old island away and made a new volcanic island. Meanwhile, the volcanoes on the old island stopped erupting.
What is a hot spot?
A hot spot is a rising plume of magma in the mantle. It remains in place while the plate above moves over it, which makes a series of volcanoes of different ages.
Name two places with hot spot volcanoes.
Hawaii and Yellowstone
What is Pangaea?
Pangaea was an ancient supercontinent, when all the continents were connected into a single gigantic landmass.
When was Pangaea on Earth?
Before the time of the dinosaurs. Plate tectonics broke it apart during dino time.
What evidence is there that shows that Pangaea actually existed?
- The continents fit together like puzzle pieces.
- There are matching rocks of the same age and type on Africa and South America, suggesting they were once connected.
- There are matching mountain ranges of the same age and type in North America, Africa, and Europe, suggesting these continents were once connected.
- There are matching signs of an ancient ice age on Antarctica, Australia, India, Africa, and South America, suggesting that these continents were once connected and that they were all close to the south pole.
- There are matching remnants of ancient environments, such as deserts and swamps, on South America, North America, Africa, and Eurasia, suggesting that these continents were once connected.
- There are matching fossils of land animals and plants (as well as a freshwater reptile) on South America, Africa, Australia, India, and Antarctica, suggesting that these continents were once connected.
Describe how sonar works, and what it shows us.
It measures the time it takes to make a sound, and then for the echo to bounce back - this shows the distance to an object.
What did sonar maps of the sea floor reveal?
Long underwater mountain ranges, called mid-ocean ridges, with rift valleys along their crests.
How do these mid-ocean ridges compare to the plates?
The mid-ocean ridges are found along the diverging boundaries of plates.
The study of ancient magnetic fields preserved in rocks is called….
Paleomagnetism
Explain how rocks can preserve magnetic fields.
When lava is still flowing, iron crystals are pointing in every random direction. Next, when the lava stops moving, the iron crystals will point north. Then, as the lava hardens into basalt, the crystals are locked in place.
Explain how paleomagnetism shows that the plates have moved.
Many basalt rocks have iron crystals that are not pointing north. This means the rock was moved after it hardened. If the rock hasn’t been moved by erosion, it must have been moved by a plate.
Describe the magnetic reversals found in the oceanic crust.
The oceanic crust has alternating bands of rock, with some having iron crystals pointing north, and others pointing south.
What could have caused the magnetic reversals found in the oceanic crust?
The north and south magnetic poles flipped, although we are not sure how this happens.
How often do magnetic reversals occur?
Magnetic reversals occur every few million years, but it is random - sometimes it is only a short period of time between reversals, other times it is a long period.
Describe the pattern of magnetic reversals found on both sides of a mid-ocean ridge.
The pattern of reversals on each side of a mid-ocean ridge is a mirror image of the reversals on the other side.
What does the pattern of magnetic reversals suggest about the formation of the ocean floor?
Since the reversal pattern matched on both sides of the ridge, it suggests that new rocks were formed at the rift valley at the top of the ridge. They recorded the magnetism at the time the formed. Later, these rocks split apart and got pushed off to the sides of the ridge, while new rocks in the rift valley recorded the new magnetic field.
What is the process where new rocks are formed at the rift valley, and then pushed apart at a diverging boundary?
Seafloor Spreading
What is the result of seafloor spreading?
Oceans grow wider and wider, and continents get pushed further and further apart.
