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?

Emil Wiechert 1 st order Structure of Earth Rock surrounding metal PLATE TECTONICS CORE-MANTLE UPPER-LOWER MANTLE INNER-OUTER CORE Time Line

5 Big Questions: - What is the Planetary K/U ratio? - Is the mantle in-gassing or de-gassing? - Distribution of volatiles in mantle? - Volatiles in the core? - Volatiles at Core-Mantle Boundary? planetary volatility curve secular changes whole vs layered convection Light element in the core hidden reservoirs

Role of Giant Impacts: volatiles Earth’s volatile budget was likely shaped by Mars-sized impacted events. Did the late veneer introduce HSE and volatiles? Differences in the volatile budget of the Earth and Moon?

What are the volatile elements? What are their abundances in the Earth? When did we inherit them? How did we inherited? Is there a secular variation in the volatile elements abundances of the Earth? More volatile questions

Volatiles: defined - H 2 O, CO 2, N 2, CH 4, (i.e., H, C, N, O) - Noble gases (group 18 elements) - elements with half-mass condensation T <1250 K - elements readily degassed (e.g., Re, Cd, Pb…) - chalcogens (group 16: i.e., O, S, Se and Te) - halides (group 17: i.e., F, Cl, Br, I)? - alkali metals (group 1: Cs, Rb, K…)?

Refractory>1400 K “Si, Mg, Fe, Ni…1350 to 1250 K Moderately volatile1250 to 650 K Volatile<650 K What are the moderately volatile elements? classifiedaffinitywhere Siderophileironcore Lithophileoxidemantle Chalcophilesulfurmostly core Redox conditions in the Solar System…..

From Palme & Jones (2003)

Heterogeneous mixtures of components with different formation temperatures and conditions Planet: mix of metal, silicate, volatiles What is the composition of the Earth? and where did this stuff come from?

Volatiles: distribution - Atmosphere (N 2 78%, O 2 21%, Ar 1%, other) - Mantle volatiles: H 2 O, C(C, CO 2, CO, CH 4 ), sulfides, etc - Core volatiles: FeC, FeN, FeO, FeS, FeH

0.1 μm- and 1.5 μm-sized olivine, pyroxene and quartz. Astro-mineralogy -- determine size, crystal structure and chemistry of dust grains in space, often around protostars (observations usually at mid-infrared wavelengths (2–30  m)). Rings around  Pictoris 63 light yrs away Okamoto et al (2004, Nature)

Mid-infrared spectroscopy (IRS) Spitzer X-ray absorption fine structure (XAFS) Chandra <2.2% crystallinity in silicate exist in diffuse 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. What’s in the ISM (interstellar medium)

Star (~1 Myr) with a clearing disk Spitzer Space Telescope Infrared Spectrograph D’Alessio et al (2005) ApJ low-mass pre–main-sequence star Glassy olivine Cleared out

Olivine Pyroxene hydrosilicate ISM HD inner disk Astro-Mineralogy Von Boekel et al (2004; Nature)

Chondrites, primitive meteorites, are key So too, the composition of the solar photosphere Refractory elements (RE) in chondritic proportions Absolute abundances of RE – model dependent Mg, Fe & Si are non-refractory elements Chemical gradient in solar system Non-refractory elements: model dependent U & Th are RE, whereas K is moderately volatile “Standard” Planetary Model

Solar photosphere (atoms Si = 1E6) C1 carbonaceous chondrite (atoms Si = 1E6) H C N Li B O

Inner nebular regions of dust to be highly crystallized, Outer region of one star has - equal amounts of pyroxene and olivine - while the inner regions are dominated by olivine. Olivine-richOl & Pyx Boekel et al (2004; Nature)

Mg/Si variation in the SS Forsterite -high temperature -early crystallization -high Mg/Si -fewer volatile elements Enstatite -lower temperature -later crystallization -low Mg/Si -more volatile elements

Pyroxene Olivine Potential temperature gradient

EH CI H LL L EL EARTH CO CM CV

EH CI H LL L EL EARTH CO CM CV MARS SS Gradients -thermal -compositional -redox 2.5 AU 1 AU Olivine-rich Pyroxene-rich

Planetary Compositional Models - Earth 1) Mg/Si -- unknown needs to be fixed 2) Hidden reservoirs -- maybe? 3) 142 Nd Early Earth Reservoir -- unlikely 4) “Chondritic Earth” -- yes, (RLE)! but… 5) Future research -- geoneutrinos -KamLAND, Borexnio, SNO+, etc

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

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

Atomic proportions of the elements

weight % elements Fe Si Mg

Volatility 1AU from Sun Th & 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 ?

Chalcophile * Siderophile * and Chalcophile * Core elements remaining in the Silicate Earth *dominant chemical characteristic, but not an exclusive definition

Abundances of element Gases in the Primitive Mantle

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

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!…

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 certain dubious undoubtedly perhaps positive proof vague suggestion unanswerable argument trivial objection pure iron uncertain mixture of all the elements When it comes to volatiles…. remember, always, the words of Francis Birch (1952)