Composition of the Earth: a more volatile elements perspective Cider 2010 Bill McDonough Geology, University of Maryland Support from:

Volatility 1AU from Sun Th & U

Allegre et al (1995) EPSL

McDonough & Sun (1995) Chem G the volatile budget?

Earth’s D/H ratio Do we really know comets D/H ratio of the oceans What do chondrites tell us? Source of water and other volatiles vs the sources of noble gases? 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: Approximate concentrations Depleted Mantle H 2 O 50 ppm; CO 2 20 ppm; Cl 1 ppm; F 7 ppm Enriched Mantle H 2 O 500 ppm; CO ppm; Cl 10 ppm; F 18 ppm Total Mantle H 2 O 366 ppm; CO ppm; Cl 7 ppm; F 15 ppm Last CIDER report on volatiles in the Earth - Saal et al 2009 Earth: 6  kgOceans: 1.4  kg Ordinary chondritic planet -- 4 oceans Carbonaceous chondritic planet oceans Enstatite chondritic planet -- ~2-4 oceans

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) Volatile Budget!

Earth’s volatiles from chondrites? Let’s hear from what Sujoy has to say!…

Mantle Siderophile elements Lithophile elements Fe, Ni, P, Os Core Atmophilie elements N 2, O 2, Ar “my Earth”

First observations -- got it right at the 1-sigma level

SCIENCE Accepted as the fundamental reference and set the bar at K/U = 10 4 Th/U = 3.5 to 4.0

MORB (i.e., the Depleted Mantle ~ Upper Mantle) K/U ~ 10 4 and slightly sub-chondritic Th/U DM & Continental Crust – complementary reservoirs DM + Cc = BSE ahh, but the assumptions and samples…

Earth is “like” an Enstatite Chondrite! 1) Mg/Si -- is very different 2) shared isotopic X i -- O, Cr, Mo,Ru, Nd, 3) shared origins -- unlikely 4) core composition -- no K, U in core.. S+ 5) “Chondritic Earth” -- lost meaning… 6) Javoy’s model? -- needs to be modified

Volatility 1AU from Sun Th & U

Core Mantle Siderophile elements Lithophile elements Ca, Al, REE, K, Th & U Fe, Ni, P, Os Atmophilie elements

U in the Earth: ~13 ng/g U in the Earth Metallic sphere (core) <<<1 ng/g U Silicate sphere 20* ng/g U *Javoy et al (2010) predicts 11 ng/g Continental Crust 1000 ng/g U Mantle ~12 ng/g U “Differentiation” Chromatographic separation Mantle melting & crust formation

This translates to 11 ppb U

Allegre et al (1995), McD & Sun (’95) Palme & O’Neill (2003) Lyubetskaya & Korenaga (2007) Normalized concentration REFRACTORY ELEMENTS VOLATILE ELEMENTS Half-mass Condensation Temperature Potassium in the core Silicate Earth ?

All peridotites are 2-component mixtures! From McDonough (1994) Melt-depletion Melt-”re-enrichment” (aka - metasomatism)

Initial results from: McDonough & Sun ‘95 - trends not pretty, but robust - trends cross chondritic pt -trends are melting products -important not to use highly-ITE Lyubetskaya & Korenaga (2007) made this mistake

Log concentrations (in ppm) degree of melting Shaded symbols denote samples with MgO 40.5%

Based on mantle samples: MgO wt% (n =330)

Mantle is depleted in some elements (e.g., Th & U) that are enriched in the continents. -- models of mantle convection and element distribution Th & U rich Th & U poor

4 most abundant elements in the Earth: Fe, O, Si and Mg 6 most abundance elements in the Primitive Mantle: - O, Si, Mg, and – Fe, Al, Ca This result and 1 st order physical data for the core yield a precise estimate for the planet’s Fe/Al ratio : 20 ± 2

What’s in the core? 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?

Model 1Model 2 Core compositional models others

Model Core composition (wt%) % in core rel. Earth (ug/g) % in core rel. Earth Fe88.387V15050 O33Mn30010 Ni5.493Cu12565 S1.996Pd3.1>98 Cr0.960Re0.23>98 P0.293Os2.8>98 C0.291Au0.5>98

REFRACTORY ELEMENTS Nature 436, (28 July 2005) Detecting Geoneutrino in the Earth Detecting Electron Antineutrinos from inverse beta -decay 2 flashes close in space and time Rejects most backgrounds  - decay

Geo-neutrinos at KamLAND Silicate Earth has ~20 ng/g U