Earth's Interior

Formation of Earth’s Compositional Layers

• Gravity and Chemical differentiaition established 3 basic divisions: core, mantle, crust based on DENSITY .

• densest: Iron→sink to the center

• least denset: outer layer

• largest layer: mantle, composed of dark SIlicated minerals(ferromaneisan)

What EQs tell us about the earth interior

• seismic waves CURVE because velocity is changed by density(depth)

• seismic waves are reflected/change direction/change speed as they hit cross discontinuities(air → water, solid → liquid)

• if Earth's density Increases: seismic waves curve down as Density increases. curve up as density decrease.

• increase in velocity→ refracted UP

• decrease in velocity → refracted DOWN

• Therefore, Velocity increases with depth(depth up(toward center), V up)

Moho

curst-matle boundary discovered by Andirijia Mohorovicic

P-wave shadow zone

P-waves

travels slow in Core than in Mantle→ core is very different

S-wave shadow zones

• because s-waves can not travel through liquid(outer core) → shadow zone in the remaining half of the earth

how did we come to the conclusion of earth interior from Waves(Seismic waves):

what we also known about earth, beside the interior:

whole earth density = 5.5 g/cm³

density of crustal rock: 2.6-3.3 g/cm³

Moment of Inertia I = 0.334 m/r²

uniform sphere has I = 0.4 m/r²

Heat flows: averages 10^6 cal/sec/cm^

Earth’s lower mantle

• The “D” layer: boundary between rocky lower mantle and liquid outer core

• cool Region: remnants(small remaining quantity of smth) of subducted lithospheric plates

• hot regions: start of deep mantle plumes

• The “D” layer:

• boundary between rocky lower mantle and liquid outer core

• cool Region:

• remnants(small remaining quantity of smth) of subducted lithospheric plates

• hot regions:

• start of deep mantle plumes

from facts, we guess

-core 90% of iron:

• evidence: denisty, moment of Inertia, P -waves, velocities meteorites

outercore is liquid:

• S-waves shadow zones. but also consistent with Earth’s magnetism. we think magnetism arise from convection currents in the outercore.

Mantle is mainly MG, Fe, Si, O with olivine in upper part, denser minerals lower down

• evidence: p,s waves velocities, solar abundances, meteorites, density, moment of inertia, experiments on candidate of minerals, xenoliths(piece of rock inside another rock)

Oceanic crust is mainly basalt:

• drilling, p,s waves velocities, moho

Continental crust is between baslt and granite:

• evidence: moho

gravity

tell us about ISOTASY

• stronger at poles, weaker at equator.Continenets are higher than oceran floor because they are less dense

Isostatic adjustment and ice ages

isostatic adjustment

Earth’s magnetism

behaves approximately like a bar magnet. but the core is too HOT to be a permanet magnet. Explained by Convection curents in the liquid Outer core: DYNAMO Theory

paleomagnetism

dating rock using magnetic field

• evidence the that earth’s magnetic field periodically reversed direction

• evidence that continent have moved

• sea-floor spreading

Earth’s internal hear engine

heatflow in the the curst

“conduction“

• conduction poor for most rocks

mantle convection

• there is no large change in temperature

• must have an effective method if transmitting hear from the core outward