Earth Structure Can you describe or draw a cross section through the Earth and label the relevant...
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Transcript of Earth Structure Can you describe or draw a cross section through the Earth and label the relevant...
![Page 1: Earth Structure Can you describe or draw a cross section through the Earth and label the relevant layers? Try?](https://reader035.fdocuments.in/reader035/viewer/2022062301/5697bfe31a28abf838cb4ce9/html5/thumbnails/1.jpg)
Earth Structure
Can you describe or draw a cross section through the Earth and label the relevant layers?Try?
![Page 2: Earth Structure Can you describe or draw a cross section through the Earth and label the relevant layers? Try?](https://reader035.fdocuments.in/reader035/viewer/2022062301/5697bfe31a28abf838cb4ce9/html5/thumbnails/2.jpg)
Earth StructureThe specification states that you need to know about:
1) Layers: Compositions, depths and physical states of:
i) Continental and oceanic crust
ii) Mantle
iii) Inner and outer Core
2) Lithosphere and asthenosphere; Describe the nature of the Lithosphere (rigid), Asthenosphere (rheid), Low Velocity Zone,
3) Discontinuities: Depth and nature of discontinuities: Inner core, outer core, mantle, continental crust and oceanic crust.
4) Direct evidence: Such as deep mines, surface rocks, volcanic vents and ophiolites.
5) Indirect evidence: Such as seismic wave velocities, shadow zones, whole earth and rock density and meteorites.
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Turn to page 11 of Chernicoff and look at the diagram showing the structure of the Earth.
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Earth StructureCrust: the upper layer which is solid (divided into 2 types).Lithosphere: the crust plus the upper part of the mantle (solid).Mantle:
Upper part is solid and is part of the lithosphere.Below this is the asthenosphere which is partly molten and can flow.Rest of mantle is solid.
Outer Core: Liquid.Inner Core: Solid.
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What are (lithospheric) plates?Lithospheric plates comprise of 2 parts:
An upper part which is crust.
A lower part which is a solid part of the upper mantle.
This makes a lithospheric plate.
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2 Types of Lithospheric Plate.Continental.
Oceanic.
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Classification of Igneous Rocks.They can be classified based on their SiO2 content:
Acid: > 66%
Intermediate 52 – 66 %
Basic 44 – 52%
Ultrabasic < 44%
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Oceanic CrustTypically made of basic igneous rocks (basalt).
7 - 10 km thick.
Density of 3.0 g/cm3
Will sink at subduction zones.
Forms at Mid Ocean Ridges and is saturated in water.
Young Jurassic to present.
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Continental CrustOn average has Acid/Intermediate composition.On average 30 km thick but can be up to 90km thick in mountain ranges.Density of 2.7 g/cm3
Will not sink at subduction zones.Old: 4 billion (Precambrian) to Present
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MANTLEMade of an olivine rich ultrabasic rock called: Peridotite.
Higher density than crust (3.3g/cm3)
Upper mantle area - solid peridotite (part of the Lithosphere).
Low Velocity Zone - (50 - 250). The LVZ is also called the asthenosphere (weak sphere) or rheosphere (flowing sphere).
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MANTLEIn this zone a very slow movement or creep is possible due to convection currents being present.The convection currents drive plate tectonics.This area is 5% partially molten peridotite. Upper Mantle - (250 - 400). Solid peridotite again.Transition Zone - (400 - 1050). Solid again and covers much of the Upper mantle. This is a transition from low-density form of peridotite to a higher density peridotite.
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MANTLELower Mantle - (1050 - 2900). Contains a higher density version of Peridotite (5.4 g/cm3).
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COREOUTER CORE
Liquid
Ni, Fe, S, K, Si
(9.9g/cm3)
INNER CORE:Solid
Ni, Fe alloy
(13.5g/cm3).
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The Driving ForceConvection Currents
Very slow convection currents flow in this asthenosphere.These currents provide horizontal forces on the plates of the lithosphere much as convection in a pan of boiling soup (must be Heinz tomato) causes a crouton on the surface of the water to be pushed sideways.
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The Driving Force 2The convection currents are driven by heat generated within the earth.
This emanates primarily from the core and is transferred to the surface by the convection currents.