Geology Chapter 12

convection

warm water rises, cold water sinks

Earth's Heat

-Earth loses most of it's heat near mid oceanic ridges, where magma rises to fill cracks formed when tectonic plates pull apart -continents emit more heat than old oceanic floor because they contain higher amounts of heat producing radioactive isotopes.

Rigidity

-liquid core has no rigidity -inner core is less rigid than the manlte

Waves

-over short distance the direct wave arrives first -for greater distances the the refracted waves arrive first -at the cross cover point, both waves arrive at the same time. the distance to the cross over point increases as the depth of the moho increases, and therefore can be used to determine the thickness of the crust at different locations

P-wave shadow zone

-rays refract downward when they hit the iron core.

seismic waves

-spread out from an earthquake source(hypocenter) as circular features called wave fronts -Using seismic velocity variations to determine properties of inner Earth

S-wave shadow zone

-waves can not pass through liquid core

What is thought to produce Earth's magnetic field?

As iron-rich fluid in the liquid outer core rises, the fluid is twisted by Earth's rotation. The flow of this electrically charged material generates a geodynamo.

core

Core is 1/6 of Earth's volume but 1/3 of Earth's mass

shape of earth

Earth is an Oblate Spheroid

Which of the following best describes the pattern of heat flow through the lithosphere?

Heat flow is high where crust is being created.

Inner Core

Solid Iron

What is the Moho, and how is its depth determined?

The Moho is the boundary between the crust and the mantle. Its depth is determined by observing where refracted seismic waves and direct seismic waves cross over each other.

Why is the asthenosphere weaker than the lithosphere?

The asthenosphere is warmer and has a lower viscosity than the lithosphere.

How do the positions of the magnetic poles change through time?

The magnetic north pole varies somewhat from the geographic North Pole while still remaining in the Northern Hemisphere. Additionally, periods of full magnetic reversals have occurred where magnetic north and magnetic south have switched places with each other. Both types of variation are caused by changes in the convection patterns within the outer core.

What characteristic of seismic waves makes them useful for probing Earth's interior?

The velocities and directions of seismic waves reliably differ when they encounter different materials within Earth.

What does a reflected wave tell us about Earth's interior?

The wave has hit a boundary between two different Earth materials, causing it to reflect back to Earth's surface.

Which of the following best describes what occurs during convection?

Warmer, less dense material rises.

What are the three compositionally distinct layers of Earth's interior?

a strong, rocky crust at Earth's surface, a hot, pressurized mantle beneath the crust, and an iron-rich core that is made of a solid inner core and a liquid outer core

Why do seismic waves travel along curved paths through the mantle?

because mineral phase changes in the upper mantle cause sudden increases in seismic velocity

Reflected waves

bounces off of core

All planets have distinct layers with most dense materials at the ________.

center

The Moho separates the ______.

crust and mantle

Geodynamo

earth's rotation causes spiral flow in the iron rich liquid outer core that aligns with the spin axis

Lower Mantle

hot, but strong because of high preasure

Athenosphere

in upper mantle, hot weak rock layer

Lithosphere mantle

in upper mantle, strong layer

outer core

liquid iron

Refracted waves

passes through core and slightly changes direction

upper mantle

rocky includes weak and strong layers

crust

strong rocky layer

One-third of Earth's mass comes from ______.

the core

What causes a mineral phase change?

the increase of pressure on a mineral when it is moved deeper within Earth