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NITROGEN IN PLANETARY SYSTEMS Barcelona 2011

NITROGEN IN PLANETARY SYSTEMS Barcelona 2011. MAGMA OCEAN. A number of models for the early Earth suggest a surface magma ocean formed during accretion with the accumulation of the most of planets volatiles in atmosphere.

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NITROGEN IN PLANETARY SYSTEMS Barcelona 2011

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  1. NITROGEN IN PLANETARY SYSTEMS Barcelona 2011

  2. MAGMA OCEAN A number of models for the early Earth suggest a surface magma ocean formed during accretion with the accumulation of the most of planets volatiles in atmosphere. A magma ocean may have formed as a result of: (i) the moon-forming impact [Zahnle, 1998; Ozima and Podosek, 2002; Selsis, 2004; Denlinger, 2005; Maurette, 2006]; (ii) impacts of planetesimals at the late accretion period [Elkins-Tanton and Seager, 2008; Lammer et al, 2008; Pechernikova and Vityazev, 2008]; and/or (iii) as a result of potential energy release during the core formation [Galimov, 2005]. Introduction

  3. THE MODEL DESIGN The magma ocean would have solidified and cooled up to 600°Сwithin 5-10 million yeas [Sleep et al., 2001; Elkins-Tanton, 2008]. Draw-down of CO2 from the atmosphere, reducing the greenhouse effect, would occur through ‘weathering’ reactions producing carbonate minerals.As soon as a liquid ocean started to condense, the alteration of surfaces rock began; as a result the first sedimentary rocks could have formed. At the same time vigorous hydrothermal systems would have been set up mining the heat from the crust and leading to metamorphic reactions changing the composition of the crust and proto-ocean. We simulated the next processes: (i) the cooling of the H2O-CO2/CH4 atmosphere with accounting of interaction with surface rocks, (ii) the same model combined with hydrothermal alteration of the protocrust, and (iii) the subaerial weathering in conditions of the CO2/CH4 atmosphere. Introduction

  4. CARBONE DIOXIDE OR METHANE? Liquid water might exist on the early Earth’s surface as early as 4.4 Ga [e.g. Mojzsis et al., 2001; Cavosie et al., 2005; Watson and Harrison, 2005]. Thus, according to the faint young Sun paradox, a greenhouse gas is necessary CH4 OR CO2 • Carbonate minerals (dolomite) described in the Isua sediments (3.8 Ga) [Myers, 2001] • The methane atmosphere could be provided in the case of a very low oxygen fugacity of upper mantle (less than 10-40-10-60 bar) [Holland, 1984] • Absence of the early Earth’s carbonate rock’s remnants [Shaw, 2008] • Inconvenience of none-highly reduced conditions for origin of life [e.g. Natochin et al., 2008] Introduction

  5. INITIAL COMPOUNDS As an analog of the early Earth’s protocrust we used the next basaltic komatiite compound from the Archean greenstone beltMunro Township (Canada) [Arndt, Nesbitt, 1982], wt. %: SiO2 = 48.76, Al203 = 9.36, Fe2O3 = 3.07, FeO = 8.04, MgO =21.65, CaO = 8.05, Na2O = 0.90, К2O = 0.16. The bulk volume of the modern Earth volatiles currently distributed between atmosphere, hydrosphere, crust and upper mantle was supposed as a composition of the atmosphere existed with the last magma ocean [MacKenzie, Lerman, 2006]. Introduction

  6. (i) DENSE H2O-CO2/CH4 ATMOSPHERE – PROTOCRUST SURFACE INTERACTIONS Result of calculations

  7. THE MODELING APPROACH DESCRIPTION For the modeling scenario (i) and (ii) we applied the equilibrium thermodynamic calculations as the atmosphere cooling process is enough extended (10-n*10 Ma [Elkins-Tanton, 2008]). The scheme of the flowing chemical reactor[Grichuk, 2000] The method description

  8. THE MODELING SYSTEM The simulations were implemented with the use of the program complex for thermodynamic calculations GEOCHEQ[Mironenko et al., 2008] and the thermodynamic constant data basederived from Supcrt92 [Johnson et al., 1992]. The modeled system:O-H-K-Mg-Ca-Al-C-S-Si-N-Na-Cl-Fe. In the course of calculations 102 minerals, 20 solid solutions, 79 solution speciesand10 gases were obtainable. Temperature changed from 600°С up to 15°С with step 25°С and pressure calculated to the sea level from the atmosphere weight. The method description

  9. WEATHERING CRUST The CO2 contained atmosphere The basaltic komatiite surface transformed into the weathering crust consisted from quartz and pyrite. SEAWATER COMPOSITION The CO2 contained atmosphere As the solution is not saturated by all cations (excepted Si and Fe) the cation composition is equivalent of its distribution in the rock: Mg > Al > Ca > Na > K > Si >> Fe. Anion composition: SCO2 >SCl- > NH4,aq > SH2S ≈SSO4 pH changed from 1 up to 0.5. Results of calculations

  10. ATMOSPHERE COMPOSITION The CO2 contained atmosphere At >375°С water started to condense and the bulk pressure decreased from 342 up to 217 bar. Then it continued to reduce gradually and achieved 44 bar at 15°С. The resulted atmosphere consisted from CO2 (43 bar), H2S and N2. The methane pressure is about 10-14 bar. Results of calculations

  11. WEATHERING CRUST The CH4 contained atmosphere The basaltic komatiite surface transformed into the weathering crust consisted from quartz and pyrite, but the pyrite was less abundant than in the case of CO2 contained atmosphere. SEAWATER COMPOSITION The CH4 contained atmosphere As the solution is not saturated by all cations (excepted Si and Fe) the cation composition is equivalent of its distribution in the rock: Mg > Al > Ca > Fe > Na > K > Si. Anion composition: SCl- > CH4,aq > NH4,aq > SH2S ≈SSO4 pH changed from 1 up to 0.5. Results of calculations

  12. ATMOSPHERE COMPOSITION The CH4 contained atmosphere During the water condensation the atmospheric pressure decreased from 307 up to 187 bar. Then it continued to reduce gradually and achieved 22 bar at 15°С. At high temperature the prevailing gases are H2O and CO. The resulted atmosphere consisted from CH4 (20 bar) and H2S. Nitrogen is fully accumulated in the hydrosphere. Results of calculations

  13. PRELIMINARY RESULTS • The atmospheric pressure reduced from 342-307 bar up to 44-22 bar as a result of the atmosphere-hydrosphere-protocrust surface system cooling; • The originated weathering crust consisted from quartz and pyrite in the both cases and didn’t contain the carbonate minerals; • The current model can’t describe the seawater composition forming Results of calculations

  14. (ii) ATMOSPHERE - HYDROSPHERE - PROTOCRUST SYSTEM (considering the hydrothermal circulation) Result of calculations

  15. HYDROTHERMAL CIRCULATION IN THE COOLING SOLIDIFIED MAGMA OCEAN. MODEL SCHEME We used a simplified model of modern hydrothermal systems in mid-oceanic ridges [Silantyev et al., 2009]. The T-P conditions in the modeled protocrust corresponds to the same parameters into modern fast-spreading ridges [Pelayo et al., 1994]. Results of calculations

  16. SECONDARY MINERALS INTO THE PROTOCRUST. The CO2 contained atmosphere Results of calculations

  17. THE WEATHERING CRUST The CO2 contained atmosphere The weathering crust mineral composition didn’t change after the hydrothermal circulation beginning Results of calculations

  18. SEAWATER COMPOSITION The CO2 contained atmosphere The seawater composition is very similar to the modern one! Anion composition: SCl- > SCO2 > NH3,aq > SSO4 Cation composition: Na > Ca > K > Mg > Fe > Si > Al At moderate temperature pH achieved a value about 5.5 Results of calculations

  19. ATMOSPHERE COMPOSITION The CO2 contained atmosphere The atmosphere composition changed drastically. CO2 removed and its pressure was 0.04 bar (the modern value is 0.0004 bar) at 15°С. The pressure of resulted atmosphere was 0.99 bar and it consisted from N2 mostly. Results of calculations

  20. SECONDARY MINERALS INTO THE PROTOCRUST. The CH4 contained atmosphere Results of calculations

  21. WEATHERING CRUST The CH4 contained atmosphere The most abundant mineral The mineral composition of weathering crust changed drastically. Hydrothermal systems supplied the surface ocean with cations and ‘oxidize’ it as the oxygen fugacity in protocrust with Qtz-Fa-Mag system is higher than in methane atmosphere. Results of calculations

  22. SEAWATER COMPOSITION The CH4 contained atmosphere The calculated seawater composition almost didn’t change in comparison with the scenario of ‘easy cooling’ Anion composition: SCl- > NH3,aq > CH4,aq >SCO2 > SH2S Cation composition: Na > K > Si > Ca > Al > Mg At 15°С pH achieved a value 10.6 Results of calculations

  23. ATMOSPHERE COMPOSITION The CH4 contained atmosphere The atmosphere composition didn’t change. Its pressure kept on the same level. The only difference is a higher pressure of N2 and a decrease of H2S Results of calculations

  24. PRELIMINARY RESULTS • The same modeling conditions for both atmosphere composition provided very different atmosphere-hydrosphere-protocrust system; • The presence or absence of carbonate minerals in the early Earth’s remnant couldn’t be a confirmation of the atmospheric composition; • In the case of CO2 atmosphere we received the seawater compound that is very similar to the modern one; • The only considerable difference of this composition is a reducing of magnesium. The possible source of Mg (as in the case of modern ocean) is a subaerial weathering Results of calculations

  25. (iii) SUBAERIAL WEATHERING Result of calculations

  26. THE MODELING SYSTEM The thermodynamic calculations with accounting of minerals dissolution were implemented with the use of the program complex GEOCHEQ[Mironenko et al., 2008]. The modeled system:O-H-K-Mg-Ca-Al-C-Si-Na-Fe. We used kinetic constants for the next minerals: albite, amorphous silica, brucite, calcite,chrysotile,clinochlore,daphnite, diopside, dolomite, enstitite,fayalite, ferrosilite, forsterite, goethite, greenalite (Fe-serpentine), illite, magnesite, magnetite, Ca, K, Na,Fe-montmorillonites, siderite, talc. Temperature was 15°С and pressure 1 bar. The system was open by CO2 or CH4 (they pressure was 1 bar). The method description

  27. THE CALCULATION PROCEDURE Primary minerals Aqueoussolution The kinetic controldissolution Secondary minerals The thermodynamic control sedimentation The calculation of chemical equilibrium [System composition](t+t) = [Solution composition]t + ΔtΣ(RateiSSSAi) Dissolved matter duringΔt The method description

  28. THE MINERAL’S DISSOLUTION RATE EQUATION The Laidler empirical equation [Laidler, 1987] The Arrhenius equation [Xu et al., 1999] The Lasaga equation [Lasaga, 1981] The method description

  29. THE WEATHERING CRUST MODELING SCHEME The single calculation duration was 0.05 year (tk) ~1 000 000 waves went throw the modeling komatiitic block Water-rock ratio was assumed to be 0.016 (rainfall = 1000 mm per year) SSSA wasfor primary minerals 1.4 m2/g and for secondary minerals – 53 m2/g tk=Σ Δt The method description

  30. THE WEATHERING CRUST The CO2 atmosphere The primary minerals dissolution sequence: Opx (32 model years) Ol, Cpx (54) Mag (60) Pl (1900). The resulted weathering crust consisted fromamorphous silica (61.8 vol. %), Fe-montmorillonite (nontronite) (35.3 vol. %), goethite (2.8 vol. %) andillite (0.06 vol. %). Results of calculations

  31. THE BULK COMPOSITION OF WEATHERING CRUST The CO2 containing atmosphere The resulted weathering crust lostMg, Ca, Na, and on the final stage Fe and K. It accumulated Si and Al. Results of calculations

  32. THE WEATHERING CRUST The CH4 atmosphere The primary minerals dissolution sequence: Opx (0.3model years) Cpx (100) Mag (615) Ol (5200)Pl (6000). The resulted weathering crust consisted fromamorphous deweylite (58 vol. %) andchlorite (42vol. %). Results of calculations

  33. THE BULK COMPOSITION OF WEATHERING CRUST The CH4 containing atmosphere The resulted weathering crust lostNa, K and Ca. It accumulated Si, Fe, Al and Mg. Results of calculations

  34. DISCUSSION Quartz + Magnetite BIF early Archean formation formed in the surface conditions Pillow basalts with age more than 3.5 Ga Discussion

  35. ABOUT ORIGIN OF LIFE The chemical compound of the earliest biont cytoplasm was probably identical to the environmental composition. In the publication [Natochinet al, 2008] has been given a supposition that the intracellular liquid’s physico-chemical parameters of modern creatures didn’t change. Therefore, the prebiotic terrestrial environment was possibly characterized by predominance of potassium above sodium (K/Na>1) and sufficiently high content of magnesium *[Natochinet al, 2008] [Novoselov and Silantyev, 2010] Discussion

  36. CONCLUSIONS • The thermodynamic calculations can’t give an answer what is the early atmosphere composition more plausible. But if the magma ocean existed with water steam – CO2 atmosphere, the tempered environmental conditions (with atmosphere and hydrosphere similar to the modern one) might be entrained very quickly . • Magnesium was removed from seawater by hydrothermal circulation and its balance determined by the subaerial continental weathering. • The presence or absence of carbonate minerals in the early Earth’s rocks remnant couldn’t be a confirmation of the atmospheric composition. Conclusions

  37. FUTURE PERSPECTIVES TO DEVELOP THIS MODEL • To develop the model of atmosphere-hydrosphere-protocrust system with accounting of the minerals dissolution kinetics. • To combine the oceanic system and continental models. • To add the isotope fractionation block and to compare the received results with Hadean zircon isotope compositions. We thank M.V. Mironenko (Vernadsky Institute) for providing programs and consultations and L.T. Elkins-Tanton (Massachusetts Institute of Technology) for the magma ocean modeldiscussion. This investigation was financially supported by program no. 25 of the Presidium of the Russian Academy of Sciences, subprogram 1, theme "Reconstruction of the Formation Conditions of the Protocrust of the Early Earth and Its Role in the Evolution of the Composition of the Primary Atmosphere and Hydrosphere" Conclusions

  38. Thanks a lot for your attention!!!

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