Chap 01 Earth Structure - utoledo.edu heat source. A quick review Lithospheric plates Supported by...
Transcript of Chap 01 Earth Structure - utoledo.edu heat source. A quick review Lithospheric plates Supported by...
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EarthStructure
note the externallayers:
HydrosphereAtmosphere
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Earth Structure
CrustMantle
Core
The Earth as ahard-boiled egg
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Earth Structure
Average density of Earth = 5.5 g / cm3
Density of crust: continents = 2.7 g / cm3
ocean floor = 3.3 g / cm3
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Density
Density = Volume
Mass
Units aregrams 1 cm (h)
1 cm (d)1 cm (w)
cm3
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Density - some examples
Water = 1.0 g/cm3 remember this
Ice = 0.917 g/cm3
Air = 0.00129 g/cm3
Iron = 7.86 g/cm3
Gold = 19.3 g/cm3
Granite = 2.65 to 2.8 g/cm3
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Density
Density = Volume
Mass
Would this demonstration workusing solids?
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Earth Structure
Average density of Earth = 5.5 g / cm3
Density of crust: continents = 2.7 g / cm3
ocean floor = 3.3 g / cm3
this difference reflects mostly a change in composition, some effect from pressure
What does it imply that oceanic and continental crust are MUCH lowerdensity than the average?
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Earth Structure: Layers (version I)
Three main layers by composition:
crustmantlecore
These are determined by seismic velocityand inferred rock composition
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How Can We Interpret the InternalLayers of the Earth?
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Seismic Waves
Different types of seismic waves
Compression and shear are determined by: direction of initial motion and characteristics of the medium
Example of diving into water
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Pressure and Shear Waves
P
S
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Seismic Waves
Primary (P) Waves -- compressionhigher velocity - arrive firstpropagate through solid or liquidsignificantly lower velocity in liquid
Secondary (S) Waves -- shearlower velocitypropagate through solid, but not through liquidcan result in “shadowing”
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P wave (Primary or “pressure”)
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Pressure wave
Propagates outward in all directions (spherical)
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Pressure wave
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S wave (Secondary or “shear”)
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Seismic Waves
Velocity of seismic waves through:
Vp Vs
Crust 5 - 7.4 3 - 4 km / sec
------------- Moho separates layers -----------
Mantle 7.9 - 8.2 4.7 - 4.8 km / sec
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Earth layers by seismic velocity
Velocity changes with material and density
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crust
Velocity structureuppermantle
lowermantle
outercore
(liquid)
innercore
(solid)
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Earth layers by seismic velocity
Note the densities of the mantle and core
rock
denserock
Fe, Niliquid
solid
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Seismic Shadow Zones
Effect of Refractionany wave bends toward the slower medium
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Tomography of the Earth’s
Interior
What is aCAT scan?
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Cross section of mantle velocity
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Imaging Mantle Plumes
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Earth Structure: Layers (version II)
Another way of looking at Earth’s interior :
defined by strength and viscosity(not composition)
LithosphereAsthenosphere
MesosphereCore
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EarthStructure
Layers
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Earth Layers: Lithosphere
lithosphere – “rock” (or “hard”)
cool, rigid rock near surface
crust and upper layer of mantle
on average: 100 km thick beneath oceans150 km thick beneath continents
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Earth Layers: Asthenosphere
asthenosphere -- “soft” (“hot Silly Putty”)
near melting point
mixture of melted, partially melted, andsolid components
flows with pressure100 - 700 km
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Earth Layers : Mesosphere
mesosphere -- “middle”
pressure dominates -- rocks are solid
most of the mantle700 - 2900 km
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Lithosphere
Relative density:
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Cross Section of Crust (and Upper Mantle)
The Moho – boundary between the Crust and Mantle
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Earth Structure: Layers
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Continents – Andes-type – Ocean subduction basins
Granite – Diorite – Basalt
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Isostasy
Buoyancy and Plasticity
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Isostasy Experiment
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Isostasy of continents
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Chemical Differentiation
Whole Earth is enriched with:ironmagnesiumnickel (core)
Crust has more:siliconoxygenaluminum
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Composition - density of compounds
Si, Al, O sialic crust
Fe, Mg, SiO4 mafic mantle
Fe, Ni metallic core
Why Differentiation?
Early evolution of the planet
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Accretion, melting, and differentiation
Accretion
Melting
Differentiation
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A quick review
Just to make a point:
In your notebook, write down the following …
Venus Mars Jupiter
Sun Moon Earth
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A quick review
A basic concept: Density
mass per unit volume
1 cm (h)
1 cm (d)1 cm (w)
In the metric system,what is the referencefor density?
Water = 1.0 g/cm3
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A quick review
The interior layers of the Earth are stratified bydensity
From the top:
Crust
Mantle
Core – outer– inner
rock
dense rock
metal (Fe, Ni)
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A quick review
How can we tell what’s inside the Earth?
Drilling to recover rocks? Does that work?
Listening around the outside. Remote sensing.
Space rocks – meteorites
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A quick review
Seismic waves: Pressure (P) and Shear (S)
compressionfastermove throughsolid or liquid
P
S
shearingslowercan NOT movethrough liquid
What produces seismic waves?
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A quick review
What can happen to seismic waves insidethe Earth?
Change velocity – What’s the relationship?
Hot : Lower Density : Lower Velocity
Shear waves stopped – by liquid material
Reflect – Off boundaries between layers
Refract – Bend to the slower material
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A quick review
Seismic wavesinside the Earth
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A quick review
“Seeing” inside the planet: Seismic tomography
One slice across the Pacific Ocean near the equator
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A quick review
text
Cold slabs sinking
Hot plumes rising
**************** Evidence of mantle convection
****************
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A quick review
Earth Structure: Layers (version II)
defined by strength and viscosity(not composition)
Lithosphere cool, tectonic platesAsthenosphere hot Silly Putty
Mesosphere largest volumeCore heat source
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A quick review
Lithospheric platesSupported by the uppermost part of the mantle welded onto the bottomof the crust
Floating on the asthenosphere
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A quick review
Different Earth materials
Si, Al, O sialic crust
Fe, Mg, SiO4 mafic mantle
Fe, Ni metallic core
Why Differentiation?
Early evolution of the planet
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Continents – Andes-type – Ocean subduction basins
Granite – Diorite – Basalt
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A quick review
The continents and ocean crustare floating
Buoyancy andisostasy