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Origin and Early Evolution of the Earth: a volatile elements perspective. Cider 2010 Bill McDonough Geology, University of Maryland. Support from:. A volatile rich planet?. Time Line. 1 st order Structure of Earth Rock surrounding metal. 1897. Emil Wiechert. 1915. CORE-MANTLE. 1925.
a volatile elements perspective
Geology, University of Maryland
1st order Structure of Earth
Rock surrounding metal
planetary volatility curve
whole vs layered convection
Light element in the core
Refractory >1400 K
“Si, Mg, Fe, Ni… 1350 to 1250 K
Moderately volatile 1250 to 650 K
Volatile <650 K
classified affinity where
Siderophile iron core
Lithophile oxide mantle
Chalcophile sulfur mostly core
Redox conditions in the Solar System…..
and where did this stuff come from?
Heterogeneous mixtures of components with different formation temperatures and conditions
mix of metal, silicate, volatiles
Okamoto et al
63 light yrs away
Astro-mineralogy -- determine size, crystal structure and chemistry of dust grains in space, often around protostars (observations usually at mid-infrared wavelengths (2–30 mm)).
0.1 μm- and 1.5 μm-sized olivine, pyroxene and quartz.
Mid-infrared spectroscopy (IRS) Spitzer
X-ray absorption fine structure (XAFS) Chandra
<2.2% crystallinity in silicate exist indiffuse ISM.
In the Galactic ISM Si exists in the form of silicates, whereas a significant fraction of S exists in the gas phase.
ISM/solar O/Si 0:63 ± 0:17
Mg/Si 1:14 ± 0:13
S/Si 1:03 ± 0:12
Fe/Si 0:97 ± 0:31
The ratio of Mg to Fe in olivine is >1.2 and 15%–37% of the total O atoms in the ISM must be contained in silicate grains.
low-mass pre–main-sequence star
Spitzer Space Telescope Infrared Spectrograph
D’Alessio et al (2005) ApJ
Von Boekel et al (2004; Nature)
HD142527 inner disk
(atoms Si = 1E6)
C1 carbonaceous chondrite
(atoms Si = 1E6)
Outer region of one star has
- equal amounts of pyroxene and olivine
- while the inner regions are dominated by olivine.
Boekel et al (2004; Nature)
Ol & Pyx
-fewer volatile elements
-more volatile elements
Potential temperature gradient
Mars @ 2.5 AU
Mg/Si -- unknown needs to be fixed
Hidden reservoirs -- maybe?
142Nd Early Earth Reservoir -- unlikely
“Chondritic Earth” -- yes, (RLE)! but…
5) Future research -- geoneutrinos
-KamLAND, Borexnio, SNO+, etc
Mg/Si -- is very different
shared isotopic Xi -- O, Cr, Mo,Ru, Nd,
shared origins -- unlikely
core composition -- no K, U in core.. S+
“Chondritic Earth” -- lost meaning…
6) Javoy’s model? -- needs to be modified
weight % elements
@ 1AU from Sun
Allegre et al (1995), McD & Sun (’95)
Palme & O’Neill (2003)
Lyubetskaya & Korenaga (2007)
in the core
Half-mass Condensation Temperature
*dominant chemical characteristic, but not an exclusive definition
Fe, O, Si and Mg
6 most abundance elements in the Primitive Mantle:
- O, Si, Mg, and – Fe, Al, Ca
This result and 1st order physical data for the core yield a precise estimate for the planet’s Fe/Al ratio : 20 ± 2
What would you like?
Constraints: density profile, magnetic field, abundances of the elements,
Insights from: cosmochemistry, geochemistry, thermodynamics, mineral physics, petrology, Hf-W isotopes (formation age)
How well do we know some elements?
Ref: Owen and Bar-Nun, in R. M. Canup
and K. Righter, eds., Origin of the Earth
and Moon (2000), p. 463
Progress Report Conclusions:
Depleted Mantle H2O 50 ppm; CO2 20 ppm; Cl 1 ppm; F 7 ppm
Enriched Mantle H2O 500 ppm; CO2 420 ppm; Cl 10 ppm; F 18 ppm
Total Mantle H2O 366 ppm; CO2 301 ppm; Cl 7 ppm; F 15 ppm
H/C ratio of the bulk silicate Earth is superchondritic, owing chiefly to the high H/C ratio of the exosphere.
H/C ratio of the mantle is lower than that of the exosphere, requiring significant H/C fractionation during ingassing or outgassing at some point in Earth history.
Hirschmann and Dasgupta (2009)
Let’s hear from what Sujoy has to say!…
Francis Birch (1952)
Unwary “readers” should take warning that ordinary language undergoes modification to a high-pressure form when applied to the interior of the Earth. A few examples of equivalents follow:
High-pressure form Ordinary meaning
positive proof vague suggestion
unanswerable argument trivial objection
pure iron uncertain mixture of all the elements