nitrogen in planetary systems barcelona 2011
DESCRIPTION
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. - PowerPoint PPT PresentationTRANSCRIPT
NITROGEN IN PLANETARY SYSTEMS
Barcelona 2011
MAGMA OCEAN
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].
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.
Introduction
THE MODEL DESIGN
Introduction
The magma ocean would have solidified and cooled up to 600°С within 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.
CARBONE DIOXIDE OR METHANE?
CO2CH4
1. Absence of the early Earth’s carbonate rock’s remnants [Shaw, 2008]
2. Inconvenience of none-highly reduced conditions for origin of life [e.g. Natochin et al., 2008]
1. Carbonate minerals (dolomite) described in the Isua sediments (3.8 Ga) [Myers, 2001]
2. 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]
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
OR
Introduction
INITIAL COMPOUNDS
Introduction
As an analog of the early Earth’s protocrust we used the next basaltic komatiite compound from the Archean greenstone belt Munro 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.
Bulk weight of the modern Earth’s volatiles, g
Composition of the H2O-CO2 atmosphere, vol. %
Composition of the H2O-CH4 atmosphere, vol. %
H2O
CNClS
1.430*1024
7.784*1022
4.890*1021
4.311*1022
1.245*1022
H2O
CO2
N2
HClH2S
90.587.400.201.390.44
H2O
CH4
NH3
HClH2S
90.397.380.401.380.44
Pressure, bar 341.75 Pressure, bar 306.85The 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 ].
(i) DENSE H2O-CO2/CH4 ATMOSPHERE – PROTOCRUST
SURFACE INTERACTIONSResult of calculations
The scheme of the flowing chemical reactor [Grichuk, 2000]
THE MODELING APPROACH DESCRIPTION
The method 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 MODELING SYSTEM
The method description
The simulations were implemented with the use of the program complex for thermodynamic calculations GEOCHEQ [Mironenko et al., 2008] and the thermodynamic constant data base derived 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 species and 10 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.
WEATHERING CRUSTThe CO2 contained atmosphere
Results of calculations
SEAWATER COMPOSITIONThe CO2 contained atmosphere
The basaltic komatiite surface transformed into the weathering crust consisted from quartz and pyrite.
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: CO2 > Cl- > NH4,aq > H2S ≈ SO4
pH changed from 1 up to 0.5.
ATMOSPHERE COMPOSITIONThe CO2 contained atmosphere
Results of calculations
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.
WEATHERING CRUSTThe CH4 contained atmosphere
Results of calculations
SEAWATER COMPOSITIONThe 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.
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: Cl- > CH4,aq > NH4,aq > H2S ≈ SO4
pH changed from 1 up to 0.5.
Results of calculations
ATMOSPHERE COMPOSITIONThe 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
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
(ii) ATMOSPHERE - HYDROSPHERE - PROTOCRUST
SYSTEM (considering the hydrothermal circulation)
Result of calculations
Results of calculations
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
SECONDARY MINERALS INTO THE PROTOCRUST.
The CO2 contained atmosphere
Results of calculations
THE WEATHERING CRUST
The CO2 contained atmosphere
The weathering crust mineral composition didn’t change after the hydrothermal circulation beginning
Results of calculations
SEAWATER COMPOSITION
The CO2 contained atmosphere
The seawater composition is very similar to the modern one!
Anion composition: Cl- > CO2 > NH3,aq > SO4
Cation composition: Na > Ca > K > Mg > Fe > Si > Al
At moderate temperature pH achieved a value about 5.5
Results of calculations
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
SECONDARY MINERALS INTO THE PROTOCRUST.
The CH4 contained atmosphere
Results of calculations
WEATHERING CRUST
The CH4 contained atmosphereThe 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
SEAWATER COMPOSITION
The CH4 contained atmosphere
The calculated seawater composition almost didn’t change in comparison with the scenario of ‘easy cooling’
Anion composition: Cl- > NH3,aq > CH4,aq > CO2 > S
Cation composition: Na > K > Si > Ca > Al > Mg
At 15°С pH achieved a value 10.6
Results of calculations
ATMOSPHERE COMPOSITIONThe 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
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
(iii) SUBAERIAL WEATHERINGResult of calculations
THE MODELING SYSTEM
The method description
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
THE CALCULATION PROCEDURE
Primaryminerals
Secondaryminerals
[System composition](t+t) = [Solution composition]t + ΔtΣ(RateiSSSAi)
Aqueous solution
The kineticcontrol dissolution
The thermodynamic control sedimentation
The calculation of chemical equilibrium
Dissolved matter during Δt
The method description
THE MINERAL’S DISSOLUTION RATE EQUATION
Rate 0 0( .)0 0 2 0( ) ( / )m T T n lH H O OH WH H
k a k k K a
)11(0 TTR
Ea
e
q
RT
Gpexp1
The Laidler empirical equation [Laidler, 1987]
The Arrhenius equation [Xu et al., 1999 ]
The Lasaga equation [Lasaga, 1981]
The method description
THE WEATHERING CRUST MODELING SCHEME
tk=Σ Δt
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 was for primary minerals 1.4 m2/g and for secondary minerals – 53 m2/g
Results of calculations
THE WEATHERING CRUSTThe CO2 atmosphere
The primary minerals dissolution sequence: Opx (32 model years) Ol, Cpx (54) Mag (60) Pl (1900).
The resulted weathering crust consisted from amorphous silica (61.8 vol. %), Fe-montmorillonite (nontronite) (35.3 vol. %), goethite (2.8 vol. %) and illite (0.06 vol. %).
Initial composition
58 model years
100 model years
800 model years
24 000 model years
SiO2
Al2O3
FeOK2O
CaOMgONa2O
СO2
H2O
48.769.36
10.800.168.05
21.650.900.000.00
36.877.118.800.095.78
16.590.41
24.340.51
37.407.118.950.105.86
16.210.30
24.070.60
50.207.19
12.450.137.725.90
0.002416.42
1.40
83.069.835.57
0.00360.001.530.000.002.54
V/Vinitial*100% 100 166 164 129 86
Results of calculations
THE BULK COMPOSITION OF WEATHERING CRUSTThe CO2 containing atmosphere
The resulted weathering crust lost Mg, Ca, Na, and on the final stage Fe and K. It accumulated Si and Al.
Results of calculations
THE WEATHERING CRUSTThe CH4 atmosphere
The primary minerals dissolution sequence: Opx (0.3 model years) Cpx (100) Mag (615) Ol (5200) Pl (6000).
The resulted weathering crust consisted from amorphous deweylite (58 vol. %) and chlorite (42 vol. %).
Initial composition
17 model years
68 model years
1200 model years
79 000 model years
SiO2
Al2O3
FeOK2O
CaOMgONa2O
CO2
H2O
48.769.36
10.800.168.05
21.650.900.000.00
46.9310.0211.05
0.075.46
24.170.020.022.26
46.349.98
11.020.014.70
24.080.000.063.81
45.299.75
10.830.004.36
23.550.000.006.22
45.979.02
11.760.000.00
23.620.000.009.62
V/Vinitial*100% 100 95 99 105 103
Results of calculations
THE BULK COMPOSITION OF WEATHERING CRUSTThe CH4 containing atmosphere
The resulted weathering crust lost Na, K and Ca. It accumulated Si, Fe, Al and Mg.
Discussion
DISCUSSION
BIF early Archean formation formed in the surface conditions
Quartz + Magnetite
Pillow basalts with age more than 3.5 Ga
Discussion
ABOUT ORIGIN OF LIFE
The chemical compound of the
earliest biont cytoplasm was probably
identical to the environmental
composition. In the publication
[Natochin et 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
* Na K K/Na Mg Ca
Amoeba proteus, mmol/kg dry matter 26 376 14.5 217 63
Mammal, mmol/l 12 - 16 150 - 160 ~11
Human intracellular liquid, mmol/l 10 160 16 26 2
*[Natochin et al, 2008]
[Novoselov and Silantyev, 2010]
Conclusions
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.
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 model discussion.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
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.
Thanks a lotfor your attention!!!