Formation of the Earth -...
Transcript of Formation of the Earth -...
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Formation of the Earth• The earth started as a hot molten blob of
metal and oxygen – 4.56 billion years ago• As the blob cooled, density differences of
the original components drove an elemental segregation.
• Metallic iron - The Earth’s core• Mg, Fe, and Si oxides - The crust• How do we know?• We know from earthquake seismology
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A Slice of the Earth
InnerCore
OuterCore
Mantle
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A Slice of the Earth
InnerCore
OuterCore
Mantle
2900km
• earthquakes travel as shear waves or compressional waves
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• shear waves only pass through SOLIDS (mantle)• So we have a “liquid” iron core. This has
important implications for other elements– Ni, S, Au, Pt, Ag, Pb dissolve in the liquid iron
• What is left is Mg, Si oxide mantle.• The mantle is not really solid, but really a “putty”
that is kept warm by the radioactive decay of 40K, 235U, 238U, and 232Th.
• Half lives of isotopes• The heating of the mantle drives convection cells.
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InnerCore
OuterCore
LowerMantle
Crust
• The mantle melt cycle (subduction/formation) enriches the crust further in Si, Na, K, Ca, and Al
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Figure 01-08
Igneousrocks
Metamorphicrocks
Sedimentaryrocks
Ocean crust
Melting
MeltingMelting
Plutonism
Burial & metamorphism
Met
amor
phism
Volcanism
Lava flowsWeathering & erosion
Deposition
Weathering& erosion
Deposition &lithification
Heatpressure& stress
Melting
Cooling &crystallization Volcanic
eruptions(lava)
SedimentsMagma
New materialadded from
depth
Fluid release& melting
Sediment
A
A
A
A
B
B
D
E
ED E
E
F
F
F
F
F
G
GG
H
H
C
CC
Copyright © Princeton University Press 2012
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What about the Oceans and the Atmosphere?
• The Earth is about 0.5% water. Where did it come from?
• The source of water in the early Earth is poorly understood ...we are lucky that it arrived.
• The gravitational attraction of the Earth retained almost all of the water.
• Surface water puts important constraints on global temperature! 0 <--> 100 oC.
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Controls on CO2• CO2 is controlled by a global scale
feedback loop with a time scale of >10,000 years
• Consider the following reactions:
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Controls on CO2• CO2 is controlled by a global scale
feedback loop with a time scale of >10,000 years
• Consider the following reactions:CaSiO3 (Wollastonite)
3H2O + 2CO2 + CaSiO3 ⇒ Ca2+ + 2HCO3- + H4SiO4
GenericWeathering Reaction
Foraminifera (bugs)
Ca2+ + 2HCO3- ⇒ CaCO3 + CO2 + H2O
Diatoms (more bugs)H4SiO4 ⇒ SiO2 + H2O
Generic Precipitation Reactions
GenericMantle ReactionsCaCO3 + SiO2 ⇒ CaSiO3 + CO2
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Atmosphere
ContinentalCrust
OceanicCrust
CaSiO3
3H2O + 2CO2 + CaSiO3 ⇒ Ca2+ + 2HCO3- + H4SiO4
CaCO3 + SiO2 ⇒ CaSiO3 + CO2
H 4SiO 4 ⇒ SiO2 + H2OCa2+ + 2HCO3- ⇒CaCO3 +CO2 +H2O
Howwouldtemperature orplatetectonics change thiscycle?
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Berner,Science1997
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Lets work with unitsCO2 (g) 0.0402 %, This is a mixing ratio
O2 20.95%
N2 78.08%
Ar 0.93%
PV= nRT, average mass gas 28.96 g/mol
%, 00/0, ppm, ppb
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Pressure
ln( PhPo ) = −
MgRT
" # $
% & ' h M = 0.029 kg/mol
R = 8.314 J/mol K
g = 9.81 m/s2
Scale height 5-6 km
Atmospheric Pressure is a force per unit area: N/m2 or a Pascal.
P0 = 101325 Pa
Pressure decreases with altitude
Ph =Po e-Mgh/RT
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Weight ofatmosphere (N)=Po*4(π)r2
r=6.37x106mP0 =101325Pa
Force=m*a(N)
Total atmospheric mass is 5.1480×1018 kg
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Unit Conversion