Earth’s InteriorTwo Perspectives

Earth’s Interior

Principle of Seismic Waves1. In a uniform, homogenous medium, a wave

radiates outward in concentric spheres and at constant velocity.

2. The velocity of a seismic wave depends on the nature of the material that it travels through. Thus seismic waves travel at different velocities in different types of rocks, varying with the rigidity and density of that rock.

Principle of Seismic Waves3. When a wave passes from one material to another, it refracts (bends) and sometimes reflects (bounces back.) Boundaries between Earth’s layers refract and reflect seismic waves.

4. P waves are compressional waves and can travel through gases, liquids, and solids. S waves are shear waves and travel only through solids.

According to Composition1. Crust

- is the outermost and thinnest layer of the Earth.

- extends from the surface to about 32 kilometers below. - underneath some mountains,the crust’s thickness extends to 72 kilometers.- beneath oceans: 7km (thin); 10km

(thickest)

Crust- is made of solid rock of two general types:

A. Scalic layer – sial, or silicon-aluminum- predominant in the upper continental crust.

B. Simatic layer - sima, silicon-magnesium

- found in the deeper portions of the crust and the ocean floors.

CrustA. Continental Crust

- rich in the elements K, Na, Al, and Si- abundant in granite

B. Oceanic Crust- rich in Fe, Si, and Mg- average composition has been compared to the rock basalt

Mohorovicic discontinuity- also called as Moho- named after the Croatian meteorologist

and geophysicist Andrija Mohorovicic (1909)

- The discovery of the mantle itself and its exact location beneath the crust was, in fact, made possible by the discovery of the Moho.

Mohorovicic discontinuity- He discovered that seismic waves came

in two separate sets. - He noticed that one set arrived earlier

than the other during the course of the quake.

- One set had traveled through denser material than the other and was slowed by it.

Mohorovicic discontinuity

Mohorovicic discontinuity

Mohorovicic discontinuity

Mantle- about 2900 kilometers from the Earth’s

surface. - It makes up about 80% of the Earth’s

total volume and about 68% of its total mass.

- mainly made up of silicate rocks, and contrary to common belief, is solid, since both S-waves and P-waves pass through it.

Mantle- is mostly made of the elements silicon,

oxygen, iron and magnesium. - The lower part of the mantle consists of

more iron than the upper part. This explains that the lower mantle is denser than the upper portion.

A. upper mantle – made of peridotite – a rock made of

minerals olivine and pyroxene. Denser than basalt.

MantleB. lower mantle

- made of perovskite – spinel, a mineral olivine exposed to high pressure and increasing depth.

- The temperature and the pressure increase with depth. The high temperature and pressure in the mantle allows the solid rock to flow slowly.

Mantle- Top of the mantle - 1000°C- Near mantle/core boundary – 3,300°C

Gutenberg discontinuity- discovered by a German seismologist,

Beno Gutenberg- also known as G or core-mantle

boundary (CMB)- 660-kilometer discontinuity – where

seismic wave velocities increase because pressure is great enough that the minerals in the mantle recrystallize to form denser minerals.

Gutenberg discontinuity

Gutenberg discontinuity

Gutenberg discontinuity

Core- a radius of about 3470 km, about same

size as Mars- Composed largely of nickel and iron.

Core- is subdivided into two layers: the inner

and the outer core. A. The outer core - is 2900 kilometers below the Earth’s surface. It is 2250 kilometers thick and is made up of iron and nickel. - The temperature in the outer core

reaches up to 2000°C at this very high temperature, iron and nickel melt.

- Earth’s outer core is molten/liquid.

CoreB. Inner core

- is made up of solid iron and nickel and has a radius of 1300 kilometers. Its temperature reaches to about 5000°C.

- The extreme temperature could have molten the iron and nickel but it is believed to have solidified as a result of pressure freezing, which is common to liquids subjected under tremendous pressure.

According to Stress or Physical Properties

- We can also distinguish several layers within the earth according to their physical state, and the way they behave when they are subjected to stresses (forces that squeezes or stretch).

Lithosphere-rocky sphere-is composed of the entire crust plus the uppermost part of the mantle.-this layer extends from the surface of the earth to a depth of 100 km.-crust and upper mantle are considered single layer since they shared similar properties.

Asthenosphere-weak sphere-is located at a depth of 100 to 350 km, within the upper mantle.-Temperatures at these depths are much higher than the lithosphere.-Rocks are very near melting points.-Is said to exhibit plastic behavior.

-Ability of the asthenosphere to flow like a fluid.-Allows the lithosphere on top to move like a raft floating in a stream.

Mesosphere-the remaining lower part of the mantle-it is solid despite the very high temperatures at this depth. -pressures are very high-rocks are so highly compressed that the component atoms are prevented from separating.

Lehmann Discontinuity

Lehmann Discontinuity

Lehmann Discontinuity

Lehmann Discontinuity

Lehmann Discontinuity