The Biogeochemistry of Soils: Soils from Stars

The Biogeochemistry of Soils: Soils from Stars

The Biogeochemistry of Soils: Soils from Stars Composition of soils on earth is arguably unexpected Soils, and Earth, not reflective of chemistry of Universe Soils reflect chemical fractionation processes since beginning of universe: Big Bang Subsequent star formation/collapse Chemical differentiation during formation of solar system Chemical differentiation during formation of Earth Late cometary additions to Earth Chemistry of Solar System 6 H He 4 O C N Ne Fe Si Mg Si Exponential decline in 2 abundance w/ atomic number (number of protons) log (solar system mass 0 fraction) Ar Ca Al Na Ni Cr Mn P ClK Ti

F Sc -2 Elements from Fe have passed through stars Solar system is dominantly H and He Cu V Sawtooth pattern Li B Be -4 Co Zn Ge SeKr Ga Sr Br Zr TeXeBa Pb As RbY Sn Mo Pt Ru PdCd CeNd Os Ir In Nb Hg Dy Ag CsLa Gd Rh Sb Sm ErYb Qu TlBi Hf Pr W In

Eu Ho Tb Re Tm Lu Ta Th U -6 0 20 40 60 atomic number 80 100 Crust vs. Solar System 6 Depleted in volatiles (as other inner planets) Noble gases (group VIIIA) H, C, N Be 4 F 2 O Al Na Si P Cl Mg 0 S

N -2 Ti Ca Sc V Ga As Mn Cu Fe Zn Br Ge Cr Co Ni ThU Ba Ta La Ce PrNd Hf SmGd Cs EuTb DHo yErTYb mLu W Nb Rb SrZr Y K Li B log (crust/solar system) C Core formation depleted crust in siderophile elements (group VIIIB..) actinides lanthanides Mo

TlPb Sn Sb In I Ag Cd Bi crust enriched Hg Re Au Se Ru Rh Pd Te Pt Os Ar Ir H period 2 period 3 He Ne period 4 crust depleted Xe Kr -4 period 5 period 6 -6

Crust also reflects late stage cometary additions of light elements, etc. including water -8 0 20 40 60 atomic number 80 100 Soil vs. Crust 2 Soil enriched in biochemically impt elements (C, N, S, Se) Soil depleted in alkali and alkine earths, Si, . Date normalized to a relatively immobile element (Zr) N 1.5 C ) Zr I Br 1 soil enriched In

/crust0.5 Se Sb As Zr S 0 log(soil Li B O -0.5 Si Al P Cl Ni Cr TiV Mn Zn Ga Fe Cu Sc KCa Co Ge Cd Zr Y Rb Sr Mo F Sn Pb Bi Hg Au Th U Nb

Mg -1 Ag Tm Dy Yb La Nd Lu Eu Cs Pr Sm Tb Gd Hf Ba Er Ta Ce Ho W Tl depleted soil Na Be -1.5 0 20 40 60 atomic number 80 100 Methods of (reasons for) Normalization to Index Element Original land surface 20% weathering loss Parent

material Soil 100 kg @ t=0 80 kg @ t=X 1) Mineralogical composition of parent material and soil Parent material 49 kg quartz (SiO) 50 kg Ca silicate (CaSiO) 1 kg zircon (ZrSiO) Soil 49 kg quartz 30 kg Ca silicate 1 kg zircon 2) Molecular weights of elements and minerals Molecular Wts (g/mole) Si=28.1 O=16.0 Ca=40.1 Zr=91.2 4) Concentrations in parent material and soil Parent material Soil Enrich/Deplete Si = .481 Ca = .238 Zr=.007 .518 .179 .009 enrich deplete enrich Formula Wts SiO=44.1 CaSiO=84.2 ZrSiO=135.3 3) Sum of elemental mass in parent material and soils 5) Elemental ratios w/ and w/o normalization No normalization Casoil/Caparent material Sisoil/Siparent material Ratio

.75 1.08 Zr Normalization (Ca/Zr)soil/(Ca/Zr)pm (Si/Zr)soil/(Si/Zr)pm Ratio .60 .86 iparent material =(31.2)quartz+(16.7)Ca silicate+(0.2)zircon= 48.1 isoil =(31.2)quartz+(10.0)Ca silicate+(0.2)zircon= 41.4 Caparent material =(23.8)Ca silicate Casoill =(14.3)Ca silicate Zrparent material/soil =(.7)zirl Weathering Losses of Elements from Soils As might be expected, water enriched relative to crust via chemical reactions 6 Ar 5 ) Zr Cl 4 C /crust Relative concentration related to chemical nature of elements and their reactivity in water and type of bonds they form in crust Zr Br S I 3

Ag Se N B 2 Ca Mg Na log(water LiBe F Zn Cu As Sr Ra Mo Bi Pb U K 1 Cr Ni Co Mn Fe V SiP 0 Hg Au Cd Sb Al Ba Ga

Rb Ti Sc Nb Zr Cs La Ce Sm Eu Tb Lu W Yb Th Hf Ta Sn -1 0 20 40 60 atomic number 80 100 Plant Composition and Soil Chemistry Plants reflect water chemistry (with some selectivity) and photosynthesis/N fixation 6 CN )

Zr 4 H Br B /crust SCl Eu I P 2 Zr Li 0 log(plant Be Mo Cd Hg KCa Zn Ag Sr Sn Bi MnCu Pb CrCo Mg Ba Tl Ni As Rb Au La Se Y Lu FNaSi Sm Yb Cs Zr Ga Fe TbDy Al

V Sb Ce W Ti U Th -2 Sc -4 0 20 40 60 atomic number 80 100 Soil Biogeochemistry Highlights 2 Biological group 1.5 Alkali/alkaline earths 1 ) Halogens Zr Rare earths 0.5 Ti group /crust Si, Al, Fe, P Zr 0 N C I Br S Zr

Ti Li log (soil Fe Si Al P Cl -0.5 Rb Sr Tm Dg Yb Nd Lu Eu Tb Cs Pr Sm Gd Hf Ba Em Ce Ho Th U KCa Mg F -1 Na Be -1.5 0 20 40 60 atomic number 80 100

Soil Mineralogy: Primary Minerals Minerals are associations of elements Mineralogical composition a function of elemental behavior and abundances O 474,000 mg/kg Si 277,000 Al 82,000 Fe 41,000 Ca 41,000 Na 23,000 Mg 23,000 K 21,000 Relative abundance and behavior leads to reality that soils are dominated by aluminosilicates (O,Si, Al). Structure of Silicates Silica tetrahedron Net charge Role of Al Covalent bonds (Si-O, Al-O) vs. ionic bonds (cations-O) Bond type based on electronegativity differences and tendency to attract electrons Big differences lead to ionic bonds Similar electronegativities lead to covalent bonds Linage of tetrahedra dictate classes of silicates and their chemical behavior Nesosilicates Inosilicates Phyllosilicates Tectosilicates Electronegativities of the Elements Electonegativities dictated by position on table: elements with outer shells almost filled highly electonegative, those just starting new shell not. Si-O form mainly covalent bond The Silica Tetrahedron 1 Si, 4 O = -4 net charge Tetrahedra can be linked by sharing O, thereby reducing net negative charge. Class of silicate is determined by number of shared O, and need for cations to neutralize net negative charge Nesosilicates: Singe Tetrahedra Linked with Cations Foresterite Single tetra linked with Mg+2 Other minerals in group have all Fe+2

Highly susceptable to chemical weathering via ejection of cations by acid (H+) Products then form secondary silicates and oxides Inosilicates: Chains Diopside: Single chains Tremolite: Double chains Phyllosilicates: Sheets Muscovite dioctahedral w/ Al+3 Phlogopite trioctahedral w/ Mg+2 K+ strongly adsorbed in cavities Tectosilicates: Framework Anorthite (Ca) 50% Al for Si substition Albite (Na) 25% Al substition Quartz No substition/O charge Primary Silicate Summary Silicate Classifiication Tetrahedron Arrangement Examples Chemical Formula of Speicific Minerals Nesosilicates independent tetrahedra olivine series (foresterite)Mg2SiO4 Inosilicates single chains

pyroxene group amphibole group double chains Phyllosilicates Tectosilicates sheets framework mica group plagioclase group feldspar group silica group (+) charge per 100 Oxygen 100 Melting Temperature (C) (fayalite)Fe2SiO4 (augite) Ca(Mg,Fe,Al)(Al,Si)2O6 (hornblende) NaCa2(Mg,Fe,Al)5(Si,Al)8 O22(OH)2 (biotite) (Mg,Fe)3(AlSi3O10)(OH)2 (muscovite) KAl2(AlSi3O10)(OH)2 (anorthite) CaAl2Si2O8 100 66 (2) 1205 (1) ~1200 (1) (albite) NaAlSi3O8 (orthoclase) KalSi3O8 (quartz) SiO2 1890 (1) 55(1)

80 ~1100 (1) 80 ~980(3) 100 1550 (1) 50 50 0 1100 (1) 1150 (1) 867 (1) (1) Data from W.A. Deer, R.A. Howie, and J. Zussman, An Introductionto the Rock Forming Minerals, Longman Group, Ltd., London (1966) (2) Va lue for endmember with no Al substitution for Si. Value will decrease in proportion to added Al. (3) From ranges reported in: D.S. Fanning, V.A. Keramidas, and M.A. El-Desoky, Micas. Chap. 12 in: J.B. Dixon and S.B. Weed (eds), Minerals in Soil Environments, 2nd Ed., Soil Science Society of America, Madison, WI (1989). Mineralogical Composition of Igneous Rocks Stability of Primary Minerals in Soils Increasing Si/O ratio increases stability More covalent bonds Fewer ionic bonds Less susceptable to acids Decreasing Si/Al ratio reduces stability Al creates charge imbalance and need for cations Presence of Fe+2 reduces stability Fe+2 oxidizes to +3 Size and charge altered and Fe is expelled

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