Chapter 4 Layers, Convection and Buoyancy

Question 1

changes reflect variations in density and composition

Answer 1

Seismic waves can change speed, frequency, and intensity depending upon the medium in which they travel. These changes reflect variations in density and composition throughout the interior of the Earth.

Question 2

Surface waves

Answer 2

that travel along an interface or surface between two layers

Question 3

Body waves

Answer 3

that travel uninterrupted through the Earth

Question 4

P-waves or primary waves

Answer 4

that are compressional waves where particles move in the direction that the energy is traveling

Question 5

S-waves or secondary waves

Answer 5

that are shear waves where particle motion is perpendicular to the direction of energy. In addition, S-waves do not travel through liquid.

Question 6

Composition of the rocks

Answer 6

When discussing the composition of rocks throughout the Earth, we are referring to the chemistry of the rocks to distinguish different layers.

Question 7

Inner core

Answer 7

a solid mass mostly made of iron and nickel.

Question 8

Outer core and geodynamo

Answer 8

liquid iron and nickel from which the magnetic field is derived due to the motion of fluids, otherwise known as the geodynamo. The core also contains sulfur, silicon, oxygen, and carbon.

Question 9

Mantle

Answer 9

this can be broken into a couple of layers, the upper being more solid than the lower more viscous and pliable layer

Question 10

Crust

Answer 10

the uppermost layer of the Earth that varies in thickness, the oceanic crust being thinner than the continental crust

Question 11

Properties of rocks

Answer 11

When discussing the properties of rocks subject to different temperatures or pressure, we use the lithosphere and asthenosphere.

Question 12

Litosphere

Answer 12

behaves rigidly and includes the crust and the upper mantle.

Question 13

Asthenosphere

Answer 13

behaves in a ductile fashion and flows over time. This part of the mantle roughly corresponds to the middle of the mantle

Question 14

Mesosphere

Answer 14

is the mantle region below the asthenosphere but above the outer core

Question 15

Convection

Answer 15

is the force that drives plate tectonics

Question 16

Radioactivity

Answer 16

is the heat engine to convection.

Question 17

Slab push

Answer 17

(or ridge push) – rising magma will push up against an ocean ridge to elevate it slightly over the surrounding oceanic plate. The elevated material acts to push the plate away from the center of the ridge. This is only a small contribution (5-10%) of the total force acting to move the plate.

Question 18

Slab pull

Answer 18

the weight of the subducting portion of the oceanic plate acts to drag the remaining portion of the plate down with it. This is the greatest force acting on moving a plate.

Question 19

Slab suction

Answer 19

the horizontal force of the continental plate that is driven by convection pushes against the subducting slab and acts to push it down the subduction zone. This is a complex force and depends on the nature of the contact between the plates. It is the smallest of the three forces.

Question 20

Buoyancy

Answer 20

is a force that opposes gravity and describes how well something floats when placed in a fluid.

Question 21

Isostatic equilibrium

Answer 21

plays an important role in whether a material will sink into the mantle or not. Think of isostasy as a state of equilibrium.