Earth Structure. CRUST MANTLE CORE MANTLE CORE CRUST CONTINENTAL CRUST OCEANIC CRUST Peridotite...
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Transcript of Earth Structure. CRUST MANTLE CORE MANTLE CORE CRUST CONTINENTAL CRUST OCEANIC CRUST Peridotite...
Earth Structure
Earth Structure
CRUST
MANTLE
CORE
MANTLE
CORE
CRUST
CONTINENTAL CRUST
OCEANIC CRUST
Peridotite (olivine & augite)
Mohorovivic Discontinuity (Moho)
Continental crust -“Granitic”Oceanic crust - “Basaltic”
This is a compositional layering of the Earth i.e. by what material the layers are made of.
Iron & Nickel
Gutenberg Discontinuity
Earth Structure
MESOSPHERE
INNER CORE
OUTER CORE
ASTHENOSPHERE
LITHOSPHERE
This is a mechanical layering of the Earth i.e. by what properties the layers have.
solid
liquid
solid (solid-state convection)
partially molten (only 1-5% molten)
solid (cool, brittle & rocky)CRUST
MANTLE
CORE
Earth Structure
Compositional
Mantle
Core
Crust
Earth Structure
Compositional
Mantle
Core
Crust
Mechanical
Lithosphere
Asthenosphere
Mesosphere
Outer Core
Inner Core
6km/s
7km/s8km/s
Continental crustOceanic crust
Upper mantle
7.8km/s Upper mantle
13km/s
8km/s
11km/s
Mantle
Outer core
Inner core
Seismic wave velocities
Continental crust
Oceanic crust
Mantle
Core
Granitic
Basaltic
Peridotite
Metallic
(Fe , Ni , S)
Metallic
(Fe & Ni)
Lithosphere
(solid/brittle)
Asthenosphere(weak / ductile)
Mesosphere
(solid)
[solid-state convection due to high pressures & temperatures over long periods of time]
Outer core
(liquid)
Inner core
(solid)
150km
250km
2,900km
5,100km
6,300km
2.7
3.0
3.3
5.5
8.0
10
14
>65%
45-52%
<45%
0%
0%
Asthenosphere
Lithosphere
Oceanic crust
Continental crust
Upper mantle
Granitic
Basaltic
Peridotite
Mid-oceanic ridge
MOHO
Depth (km) Geotherm (°C) Melting point of Peridotite (°C)
0 15 1200
50 1250 1350
200 1450 1600
500 1900 2100
1000 2500 3000
2000 3250 3600
3000 4000 3850
4000 4250 4050
5000 4250 4200
6000 4250 4500
Temperature Variation within Earth’s Interior
1. Plot the data onto graph paper, with depth on the vertical axis.
2. Describe how the geotherm varies with depth.
3. Define the geotherm.4. Locate the Earth’s
internal layers on the graph.
5. Describe the physical state of the Earth’s interior in relation to the melting point curve.
6. Calculate the average geothermal gradient for the first 50km into the Earth.
Temperature Variation within Earth’s Interior
Depth (km)
Temperature (°C)
Inner Core
(solid)
Outer Core
(liquid)
Asthenosphere (semi-solid)
Mesosphere (solid)
Temperature Variation within Earth’s Interior
GeothermMelting curve
Depth (km)
Temperature (°C)
Inner Core
(solid)
Outer Core
(liquid)
Lithosphere (solid)
Asthenosphere (semi-solid)
Mesosphere (solid)
Where does this heat come from?
• Radiogenic heat
• Primordial heat
Oceanic Continental
Age
Thickness
Density
Composition
Structure
Formation
<200 million years<4000 million years
6-10km35km (rift valleys) – 70km (mountains)
3.0g/cm3 2.6 – 2.7g/cm3
Basaltic Granitic
Sediments, Pillow lavas, Sheeted dykes, Gabbro
Upper crust, lower crust
Sea-floor spreadingSubductionContinental collision
Evidence for Earth Structure
• Seismic Waves
• Density of Earth
• Earth’s Magnetic Field
• Meteorites
Seismic Waves
2. Body Waves
1. Surface Waves i). L-Waves (long waves)
i). P-Waves (push waves)
ii). S-waves (shake waves)
• travel through liquids & solids
• fastest waves (4 – 7km/s)
• travel through solids only
• slower than P-waves (2 - 5km/s)
both travel faster as material gets more rigid & less compressible
1
23
4
5
67
Seismic Waves Velocity
LithosphereAsthenosphere
Mesosphere Outer Core
Inner Core
Asthenosphere
Lithosphere
Oceanic crust
Continental crust
Upper mantle
Granitic
Basaltic
Peridotite
Mid-oceanic ridge
MOHO
Continental crust
Oceanic crust
Mantle
Core
Granitic
Basaltic
Peridotite
Metallic
(Fe , Ni , S)
Metallic
(Fe & Ni)
Lithosphere
(solid/brittle)
Asthenosphere(weak / ductile)
Mesosphere
(solid)
[solid-state convection due to high pressures & temperatures over long periods of time]
Outer core
(liquid)
Inner core
(solid)
150km
250km
2,900km
5,100km
6,300km
6
7
8
7.8
13
8
11
2.7
3.0
3.3
5.5
8.0
10
14
>65%
45-52%
<45%
0%
0%
Seismic Waves Refraction
Focus
Seismograph Station
Layer 1
(Crust)
Layer 2
(Mantle)
Boundary between layer 1 & 2
(Moho)
•Direct
•Reflected
•Refracted
h = depthХd = distance from epicentre where all seismic waves arrive at same timeV1 = velocity of P waves in layer 1V2 = velocity of P waves in layer 2
Epicentre
Seismograph Station 2
Suppose the shadow zone for P waves was located between 120 and 160º rather than 103 and 142º. What would this indicate about the size of the core?
Why is there a S-wave shadow zone?
There is a S-wave shadow zone from where the S-waves cannot reach the other side of the Earth as they are stopped by the liquid outer core. Liquids cannot transmit shear waves due to the weak bonding between particles.
Meteorites
Stony Meteorites
Meteorites
Iron Meteorites
Density
Earth’s Magnetic Field