Plate Tectonics Unit

What causes convection currents in Earth's mantle?

Heat from the core and the mantle itself causes convection currents in the mantle.

Break in Earth's crust where rocks have slipped past each other

fault

means to change form or appearance

transform

What are convection currents?

A convection current is the flow that transfers heat within a fluid.

What three factors set convection currents in motion?

Heating and cooling of the fluid, changes in the fluid's density, and the force of gravity

What happens to convection currents when the liquid or gas is no longer heated?

Without heat, convection currents eventually stop.

name the letter of each sentence that is true about mid-ocean ridges. a. The mid-ocean ridges were mapped using sonar. b. The mid-ocean ridges are found only below the Pacific Ocean. c. The mid-ocean ridges are completely under water. d. The tops of some mid-ocean ridges are split by a steep-sided valley.

a. and d.

What process in Earth's interior causes subduction and sea-floor spreading?

convection currents

Is the following sentence true or false? Earth looks the same today as it did millions of years ago.

false

Is the following sentence true or false? Plates can carry continents or parts of the ocean floor but not both.

false

Is the following sentence true or false? The asthenosphere is not considered solid because it can bend like plastic.

false

Is the following sentence true or false? The heat source for the convection currents in the mantle is the sun.

false, outer core

Most divergent boundaries occur along ___________________________.

mid ocean ridge

A deep valley that forms along divergent boundaries.

rift valley

Deep valley that forms where two plates pull apart

rift valley

How are the movement of plates at divergent boundaries and at transform boundaries similar?

they both move horizontal

what happens when two plates carrying continental crust collide?

they squeeze together to form a mountain range

Is the following sentence true or false? The pieces of the supercontinent Pangaea began to drift apart about 225 million years ago.

true

Is the following sentence true or false? The theory of plate tectonics explains the formation, movement, and subduction of Earth's plates.

true

means to come together toward one point

converge

where two plates come together

convergent boundary

A long, narrow and very deep canyon where the ocean floor bends down toward the mantle is called a _______________________.

deep ocean trench

means to move in different directions from a common point

diverge

is when 2 plates move apart from from one common point

divergent boundary

A device that bounces sound waves off underwater objects is called _________________.

sonar

A device that scientists use to map the ocean floor is _________________.

sonar

The process that continually adds new material to the ocean floor is called _________________.

sea floor spreading

Explain what force caused the movement of the continents from one supercontinent to their present positions.

Convection currents in the mantle is the force that caused the movement of the plates that carry the continents.

What happens to old oceanic crust as new molten material rises from the mantle?

Older rock moves outward on both sides of the mid ocean ridge.

State the theory of plate tectonics.

Pieces of Earth's lithosphere are in slow constant motion driven by convection currents in the mantle.

When two plates converge, the result is called a(n) _________________.

collision

What is sonar used for?

Sonar is used to determine the distance to an object.

Why is the Atlantic Ocean expanding?

The Atlantic Ocean has only a few short trenches. The spreading ocean floor has nowhere to go.

Compare and contrast the asthenosphere with the lithosphere.

The asthenosphere and lithosphere are both part of the mantle, however, the asthenosphere is the soft layer and is bendable just below the lithosphere and the lithosphere is the rigid layer that includes the upper part of the mantle and the crust.

How did drilling samples show that sea-floor spreading really has taken place?

The farther away from the ridge the samples are taken the older the rock. the newest rock is always in the center of the ridges.

Was Pangaea the only supercontinent to have existed? Explain your answer.

The movement of Earth's plates has greatly changed Earth's surface. Geologists have evidence that, before Pangaea existed, other supercontinents formed and split apart over billions of years.

When two plates collide, what determines which plate comes out on top?

The plate that is less dense.

Soft layer just below the lithosphere is the ___________.

asthenosphere

soft layer of rock in the mantle

asthenosphere

Circle the letter of the sentence that describes what happens to a fluid when its temperature increases. a. Its particles occupy less space. b. Its density decreases. c. Its particles move more slowly. d. Its particles settle together more closely.

b.

name the letter of each sentence that is true about convergent boundaries. a. Where two plates carrying oceanic crust meet, subduction does not take place. b. An oceanic plate sinks beneath a continental plate when the two plates collide. c. Where two plates meet, the one that is more dense sinks under the other. d. Mountain ranges form where two plates carrying continental crust collide.

b., c., and d.

Is the following sentence true or false? At deep-ocean trenches, conduction allows oceanic crust to sink back into the mantle.

false, subduction

breaks in Earth's crust where rocks have slipped past each other—form along these boundaries

fault

Rigid layer that includes the upper part of the mantle and the crust is the __________.

lithosphere

the uppermost part of the mantle and crust together

lithosphere

A chain of underwater mountains along which sea-floor spreading occurs is a _________________.

mid-ocean ridge

In sea-floor spreading, where does new crust come from?

molten material that erupts and cools.

List three types of evidence for sea-floor spreading.

molten material, magnetic stripes, and the ages of the rocks themselves from drilling samples of rocks

Line where the edges of Earth's plates meet

plate boundary

pieces of Earth's lithosphere are in slow, constant motion, driven by convection currents in the mantle.

plate tectonics

The separate sections or cracks in the lithosphere are called _______.

plates

The process by which the ocean floor sinks into the mantle is called _________________.

subduction

convection currents in the Earth's mantle causes __________.

subduction

What is subduction?

subduction is the process by which ocean floor sinks beneath a deep ocean trench and back into the mantle.

Heat transfer by convection is caused by differences of_______________ and density within a fluid.

temperature

sea floor spreading results in _______________________________________________.

the change of size and shape of the ocean

what happens when oceanic crust collides with a plate carrying continental crust?

the denser oceanic crust is subducted

what happens when two plates carrying oceanic crust collide?

the denser plate sinks below the other one at deep ocean trench

What is convection?

the movement of currents within a fluid

is a place where two plates slip past each other, moving in opposite directions.

transform boundary

Is the following sentence true or false? Crust is neither created nor destroyed along a transform boundary.

true

Is the following statement true or false? The Pacific Ocean is shrinking.

true