Banded Iron Formation (BIF)Banded Iron Formation (BIF)

- chemical sediments- Fe rich (20 - 40 wt.%)

- SiO2 rich (40 - 60 wt.%)- hematite, magnetite, siderite, chert main minerals

- laminated on various scales- ferric hydroxide, amorphous silica, greenalite &

siderite primary precipitates

Klein (2005)

Globally DistributedGlobally Distributed

Distribution peak at Archean-Paleoproterozoic transition

(real or artifact?)

Distribution peak at Archean-Paleoproterozoic transition

(real or artifact?)

The Hamersley BIFThe Hamersley BIF

over 1013 Tons of Fe

100s of meters thick

areal extent > 100,000 km2

low metamorphic grade

laterally continuous

hydrothermal Fe supply

~1 mm / yr deposition rate

over 1013 Tons of Fe

100s of meters thick

areal extent > 100,000 km2

low metamorphic grade

laterally continuous

hydrothermal Fe supply

~1 mm / yr deposition rate

1. Fe(II) oxidation

2. Diagenetic reactions

3. Solute sorbents - biosignatures

1. Fe(II) oxidation

2. Diagenetic reactions

3. Solute sorbents - biosignatures

How are microbes involved?How are microbes involved?

1. Fe(II) Oxidation1. Fe(II) Oxidation

Si(OH)4Si(OH)4

Fe2+Fe2+

photic zonephotic zone

Hamersley Group BIFHamersley Group BIF

volcanic basement volcanic

basement (1) Oxygenic Photosynthesis

2Fe2+ + ½O2 + 5H2O 2Fe(OH)3 + 4H+

6Fe2+ + ½O2 + CO2 + 16H2O [CH2O] + 6Fe(OH)3 + 12H+

UVUV

chemocline ?chemocline ?

shelf shelf carbonate

sill carbonate

sill

(2) Photoferrotrophy4Fe2+ + 11H2O + CO2 [CH2O] + 4Fe(OH)3 + 8H+

(3) Photooxidation 2Fe2+ + 2H+ 2Fe3+ + H2↑

Evidence for PhotoferrotrophsEvidence for PhotoferrotrophsA number of experimental studies have shown that various purple and green phototrophic bacteria can use Fe(II) as a reductant during photosynthesis (e.g., Widdel et al., 1993; Heising et al., 1999).

A number of experimental studies have shown that various purple and green phototrophic bacteria can use Fe(II) as a reductant during photosynthesis (e.g., Widdel et al., 1993; Heising et al., 1999).

from Posth et al. (2007)from Posth et al. (2007)

deposition rate (mm/yr) 1.00

depositional area (m2 ) 1 x 1011

mesoband volume (m3) 1 x 108

mesoband density (g/m3) 4.6 x 106

mesoband mass (g) 4.6 x 1014

FeTOTAL (%) 54.6

mass of Fe (g) 2.5 x 1014

moles of Fe 4.5 x 1012 (45 mol/m2)

Fe-Rich MesobandsFe-Rich Mesobands

from Konhauser et al. (2002)

experimental metabolic rate 9.5 x 10-3 mol Fe/L produces

(Ehrenreich & Widdel, 1994) 9.6 x 10-4 mol C/15 d

composition (mol C/cell) 3.3 x 10-14

metabolic rate (mol Fe/cell/yr) 8.0 x 10-12

total number of cells 5.7 x 1023

volume of photic zone (ml) 1 x 1019

cell density (cells/ml) 5.7 x 104

Chromatium Fe(II) Oxidation RatesChromatium Fe(II) Oxidation Rates

from Konhauser et al. (2002)

Nutritional Requirements (P)Nutritional Requirements (P)Fe-rich mesoband Average concentration (mg/kg) 713.1 (4.2)

Amount in annual BIF layer (mg) 3.3 x 1014

Gallionella Cell wet mass (g) 1.0 x 10-12

Single-cell requirement (μg/g) 9000

Single-cell concentration (mg) 9.0 x 10-12

Number of cells needed to form BIF 4.3 x 1023

Annual biomass requirement (mg) 3.9 x 1012

Number of supportable populations 85

Chromatium Cell wet mass (g) 2.7 x 10-12

Single-cell concentration (mg) 2.4 x 10-11

Number of cells needed to form BIF 5.7 x 1023

Annual biomass requirement (mg) 1.4 x 1013

Number of supportable populations 25

Rhodobacter Ferrooxidans

from Kappler et al. (2005)

from Kappler et al. (2005)

from Posth et al. (2008)

Evidence for PhotooxidationEvidence for Photooxidation

Cairns-Smith (1978) proposed that Fe(II) was photooxidized in acidic waters exposed to UV radiation with wavelengths between 200-300 nm.

2Fe2+(aq) + 2H+ + hv 2Fe3+(aq) + H2↑

Ferric iron is subsequently hydrolyzed and precipitated as ferric hydroxide.

2Fe3+ 2Fe(OH)2+ + 2H+ 2Fe(OH)2+ + 4H+ 2Fe(OH)3 + 6H+

Braterman et al. (1983) showed lower energy light (406 nm) was an effective oxidant at near-neutral pH due to the presence of Fe(OH)+

Cairns-Smith (1978) proposed that Fe(II) was photooxidized in acidic waters exposed to UV radiation with wavelengths between 200-300 nm.

2Fe2+(aq) + 2H+ + hv 2Fe3+(aq) + H2↑

Ferric iron is subsequently hydrolyzed and precipitated as ferric hydroxide.

2Fe3+ 2Fe(OH)2+ + 2H+ 2Fe(OH)2+ + 4H+ 2Fe(OH)3 + 6H+

Braterman et al. (1983) showed lower energy light (406 nm) was an effective oxidant at near-neutral pH due to the presence of Fe(OH)+

calyxa.best.vwh.net/.../ 1images/sunlight.jpg

Receiving solution:

0.56 M NaCl

± 0.0021 M SiO2 as Na2SiO3(H2O)9 ± 0.0059 M HCO3

- as NaHCO3

pH adjusted by concentrated HCl/NaOH

from Konhauser et al. (2007)

Photooxidation ResultsPhotooxidation Results

ShallowModel

%Fe(II) vs. Fe(III)-minerals ??

Fe(II)S >> Fe(OH)3

Fe(OH)3 > Fe(II)S

seamount

O2?100 m?

seamount

UV-A

UV-C

photic zone

DeepModel

UV-A

UV-C

photic zone

deep mixing zone

1 km?

100 m?

shelf

upwell

ingMOR

HematiteMagnetiteSiderite

Minnesotaite

Quartz

Apatite

2. Diagenetic Reactions

FeFe(OH)3+ SiO2+ H2PO4

-

+ metals

UVUV

Geobacter MetallireducensGeobacter Metallireducens

from Lovely et al. (1987)

Diagenetic MagnetiteDiagenetic Magnetite

Diagenetic Siderite

from Mortimer and Coleman (1997)

Rouxel et al. (2005)

Johnston et al. (2008)

Fe O3 4

Fe-rich layers

photoautotrophicFe(II)-oxidation

Fe(OH)biomass

3

methanogenesis

CH4

CH4

H2

Fe2+

Fe2+

Fe / HCO2+ -3

CO2

100

m40

0 m

5.9 mol C m-2

90.0 mol Fe(III) m22.5 mol C m (Fe:C = 4:1)

-2

-2

0.7 mol C m (as Fe O ) (Fe:C = 36:1)

-23 4

6.6 mol C m (as FeCO )(Fe:C = 4:1)

-23

26.2 mol Fe(III) m-2

63.8 mol Fe(III) m15.9 mol C m (Fe:C = 4:1)

-2

-2

wind-mixed surface layer (O present)2

anoxic deep waters

annual deposit

sedi

men

t at io

n

1 m

m

SiO -rich layers 2mid-oceanridge

(CH COO , H )3 2-

methanotrophyCH / Fe(OH)4 3

fermentation Fe(III)-reduction

from Konhauseret al. (2005)

Fe(III) Reduction

CH3COO- + 8Fe(OH)3 8Fe2+ + 2HCO3- + 15OH- +

5H2O

Magnetite Formation

8Fe2+ + 16Fe(OH)3 + 16OH- 8Fe3O4 + 32H2O

Photosynthetic Fe(II) Oxidation

4Fe2+ + CO2 + 11H2O CH2O + 4Fe(OH)3 + 8H+

Fe O3 4

Fe-rich layers

photoautotrophicFe(II)-oxidation

Fe(OH)biomass

3

methanogenesis

CH4

CH4

H2

Fe2+

Fe2+

Fe / HCO2+ -3

CO2

100

m40

0 m

5.9 mol C m-2

90.0 mol Fe(III) m22.5 mol C m (Fe:C = 4:1)

-2

-2

0.7 mol C m (as Fe O ) (Fe:C = 36:1)

-23 4

6.6 mol C m (as FeCO )(Fe:C = 4:1)

-23

26.2 mol Fe(III) m-2

63.8 mol Fe(III) m15.9 mol C m (Fe:C = 4:1)

-2

-2

wind-mixed surface layer (O present)2

anoxic deep waters

annual deposit

sedi

men

t ati o

n

1 m

m

SiO -rich layers 2mid-oceanridge

(CH COO , H )3 2-

methanotrophyCH / Fe(OH)4 3

fermentation Fe(III)-reduction

It is possible that chemolithoautotrophic bacteria, such as the microaerophilicGallionella ferruginea, may have co-existed with the photoferrotrophs. The former might have oxidized a fraction of dissolved Fe(II) that diffused upwards through the layer of anoxygenic phototrophs above the chemocline, using O2 as the electron acceptor:

6Fe2+ + 0.5O2 + CO2 + 16H2O CH2O + 6Fe(OH)3 + 12H+

From Konhauser et al., 2005

There may have been a non-quantitative association of cells with ferric hydroxide, such that some cells remained in water column while Fe(OH)3 sinks.

polymers(proteins, polysaccharides, lipids, nucleic acids, etc.)

hydrolysis

monomers and oligomers(peptides, amino acids, sugars, fatty acids, glycerol, nucleotides)

propionate, butyrate, lactate, aromatics,

other products

acetateCO + H2 2

formate methylcompounds

CH4

primary fermentation

secondary fermentation

methanogenesis

acetogenesis

fatty-acid oxidisingbacteria (syntrophs)

methanogenesism

ethanogenesis

fermentative bacteria

homoacetogens

methanogens methanogens

methanogens methanogens

hydrolyticbacteriaDuring burial, the biomass would

have been converted into DOC and H2 via fermentation, a fraction of which could have diffused away from the immediate environment, relative to the immobile ferric hydroxide. It would then have been tied to another form of microbial respiration (Walker, 1984).

The most likely would have been methanogenesis.