Physical Geology Chapter 12: Earth's Interior

Lower Mantle

Lies between transition zone ans the liquid core. Earths largest layer, occupying 56% of the volume of the planet.

Outer Core

Liquid iron rich layer 1410 miles thick. S waves do not penetrate the outer core. Their absence in the outer core indicates its liquid state. Movement of metallic iron w/in this zone generates earths magnetic field.

Transition Zone

Lower portion of the upper mantle is called transition zone.

P & S Waves

P & S Waves from these strong earthquakes act like medical X rays and provide the means to look into our planet. Speed at which these waves travel through earths interior depends on the properties of the materials that transmit them.

Seismic Waves

The use of earthquake waves, to study Earths interior has been greatly enhanced during the past decade due to the growing number of seismograph networks that can detect these waves from distant earthquakes. *Earthquake waves provide a valuable tool for studying earths interior.

Lithosphere

Uppermost mantle and crust make up earths rigid outer shell.

Lithospheric mantle

Uppermost mantle, ranges in thickness from few km under mid oceanic ridges to perhaps as much as 200 km under the stable continental interiors.

Mantle Plumes

A mass of hotter than typical mantle material that ascends towards the surface, where it may lead to igneous activity. These plumes of solid yet mobile material may originate as deep as the core mantle boundary.

Phase Change

As the ratios change, atomic structure of a mineral may become unstable, causing the atoms to rearrange into a more stable and denser atomic structure.

Inner Core

At earths center lies the inner core, a solid dense sphere. Sphere shape unlike the other layers which are shells. Inner core is relatively small. Despite high temps, iron in inner core is solid due to immense pressures. Today, inner core continues to grow larger- at expense of outer core.

Mantle

Beneath Earths crust lies the mantle. 82% of earths volume contained in mantle. Solid rocky layer rich in iron and magnesium. (S waves pass through). Rock in the mantle is hot and capable of flow.

Asthenosphere

Beneath lithospheric mantle is weak layer called asthensphere.

Inge Lehman

Boundary between solid inner core and liquid outer core was discovered in 1936 by Lehman. He discovered that some P waves were strongly refracted (bent) by a sudden increase in seismic velocities at a boundary within earths core.

Moho

Boundary between the crust and mantle.

Volcanism

Carries water and gases from earths interior to replenish our oceans and atmosphere, allowing life to exist at the surface.

Core

Composition of the core is thought to be an iron-nickel alloy, with minor amounts of oxygen, silicon and sulfur. Extreme pressure found in core. 1/6 of earths volume, 1/3 of its mass. Core is composed mostly of iron (greatest density). Composed of 2 zones: outer & inner core.

Heat travels from earths interior to space via 3 different mechanisms:

Convection, conduction, and radiation. *Convection & conduction operate w/in earths interior. *Radiation transports heat away from earths surface and eventually back to space.

Seismic waves follow strongly..

Curved (refracted) paths.

The interior of our planet remains very ________?

Dynamic * Rocks of the crust and mantle are in constant motion.

Crust

Earths relatively thin, rocky outer skin, and two types exist: continental crust (consists of many rock types) and oceanic crust (rocks of oceanic crust are younger/denser).

Negative vs Positive Ions

Easier to compress negative ions than positive ions. Negative ions have more electrons than protons and tend to be fluffier than positive ions. When rocks are squeezed, negative ions compress more easily than positive ions, so rations of ionic sizes change.

Upper mantle

Extends from the Moho to depth of 660 km (410 miles). Divided into 3 shells: lithospheric mantle, asthenosphere and transition zone.

How does gravity affect density?

Gravity affects the density of rocks bc rocks are compressed by the weight of material above them. The density of rocks increases with depth. Increase in density occurs bc atoms (ions) shrink and occupy less space when subjected to immense pressure.

The D" Layer

Highly variable and unusual region called D" layer. (Lower mantle) The D" layer, the boundary layer between the rocky mantle and the liquid iron outer core, has large variations in composition and temperature.

Chemical Convection

Is an important mechanism operating in the outer core.

Viscocity

Scientists usually measure a materials fluidity in terms of its resistance to flow, called its viscosity. Water flows easily and has a low viscosity.

Diffraction

Seismic waves can also bend when they pass by a curved surface such as a boundary between two compositionally different layers- a process called diffraction.

Oceanic/Continental Crust Wave Movement

Seismic waves travel faster through oceanic crust, composed of basalt, than through the continental crust, composed of granite.

Inner core rotates faster than..

The crust ans the mantle , lapping them every few hundred years.

Conduction

The flow of heat through material is called conduction. Heat conducts in 2 ways: through the collisions of atoms and through the flow of electrons. Occurs much more quickly in metals than in rocky substances. Materials conduct at vastly different rates.

Gravity

The force of gravity is responsible for the layering we detect in Earths interior.

Refracted

The remaining energy passes through the boundary and is refracted (bent). This is similar to how light is refracted (bent) as it passes from air to water.

Seismic waves travel fastest when..?

The rock is stiff or less compressible. These properties are used to interpret the composition and temperature of the rock at various depths. When rock is heated it becomes less stiff, and earthquake waves travel through it more slowly.

Seismic waves do not travel along a straight path, instead...

They are reflected, refracted, and diffracted as they pass through our planet.

Convection

Transfer of heat in a fluid like manner, where hot materials displace cooler materials is called convection. Primary means of heat transfer w/in earth. Convection occurs bc of: thermal expansion, gravity induced buoyancy, fluidity.

P Waves

When P waves travel through molten or partially molten rock, they travel much slower than if the rock was solid.

S Waves

When S Waves enter the outer core, which is liquid, the waves are not transmitted at all bc S waves do not travel through liquids.

Reflected

When a seismic wave hits a boundary between different earth materials, such as the boundary between the crust and the mantle, some of the waves are reflected back towards the surface.

Shadow Zone

Zone between 105 and 140 degrees from an earthquake epicenter. Direct waves do not penetrate the shadow zone, bc of refraction by Earths core.