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