Paleobiogeochemistry, Anoxygenic Photosynthesis, and Banded Iron Formations

Im a BM wrote:
Nitrate reducing iron oxidizing bacteria in plausible symbiosis

There may have been a place in the sea where the concentration of nitrite in the water was sufficient to support nitrite-based photosynthesis.

However, few such places would have occurred where there is not also more than enough ferrous iron(II) to support iron based anoxygenic photosynthesis.

Ferrous iron(II) is a stronger reductant than nitrite. The bacteria who use iron(II) as reductant for photosynthesis can outgrow the ones who use nitrite as reductant for photosynthesis.

BUT, if a nitrite oxidizing photo bacteria teamed up with an iron oxidizing nitrate reducer, it would be a win-win in more than one way.

This partnership would continuously deplete the available ferrous iron for photosynthesis, at the same time it would continuously replenish the nitrite supply. The photobacteria gives the nitrate to an iron oxidizer, who then takes out the ferrous iron from solution. Starve the competition. And then the nitrate reducer turns that nitrate back into nitrite for use in photosynthesis. More food for the home team. Recycling the nitrogen its partner needs while depriving the competition of the iron it needs.

Such a symbiosis could have created a narrow zone of low ferrous iron in the high light zone, where nitrite based photosynthesis could dominate despite the abundance of ferrous iron in the underlying water.

Nitrate is the second best terminal electron acceptor out there, after oxygen, for an organism to get maximum energy yield from oxidation of organic carbon, ferrous iron(II), arsenite arsenic(III), hydrogen sulfide, hydrogen gas...

Nitrite based anoxygenic photosynthesis produced a strong oxidant, enabling these bacteria to offer a stronger oxidant to the partner who might assist by depriving the competition of stronger reductants.

Im a BM wrote:
Sulfide and pyrite formation - correspondence report

Yesterday I reestablished contact with paleobiogeochemistry community.

I want to report on this correspondence so it isn't just buried in someone's email files.

The question was about the fact that sulfide in sea water can react with ferrous iron to form iron pyrite.

It begs the question, after episodic vulcanism loads the sea with hydrogen sulfide, how much of it can really be available for sulfide-based anoxygenic photosynthesis if sulfide is getting taken out of solution and sequestered into iron pyrite?

In a tangent off the point, the following came up that I want to transcribe, sort of, here on this thread.

The basic idea is that a photosynthetic community can create a very narrow exclusion zone at the surface, while everybody else has to stay down in the shade beneath them.

For example, with sulfide.

If there is sulfide available, sulfide based anoxygenic photosynthesis will outcompete iron based photosynthesis.

But the iron based photo bacteria can still compete by creating an exclusion zone at the surface. They can team up with bacteria that use the ferrric iron they produce as a waste product, and oxidize sulfide with it.

If a thin dense community of iron based photosynthetic bacteria formed a mat or film at the surface, they could exclude sulfide from getting in.

Without sulfide, their faster growing sulfur based photo bacteria don't have a chance.

The iron based photo community is generating ferric iron and feeding it exclusively to symbiotic bacteria they associate with. Those bacteria use ferric iron to take sulfide out of solution, sequestering into iron pyrite.

One photosynthetic community, using a WEAKER reductant, can enlist the assistance of an oxidizing bacteria to remove the competitors stronger reductant.

The community that ought to be at a disadvantage is actually on top.

And cyanobacteria certainly did this in symbiosis with iron oxidizers.

A thin mat at the surface allowed them to control the local chemistry.

Their iron oxidizing partners waited below to have exclusive access to the precious oxygen being produced. Using that oxygen to oxidize ferrous iron, and cause ferric iron to rain down on the sea floor.

With a stronger reductant, iron based photo bacteria should be more competitive. But only if they can get it.

So, a very thin zone at the top is one photosynthetic community, and everyone else is stuck in the shade beneath them.

Those cyanobacteria in that thin mat on the surface are emitting oxygen to the atmosphere on one side.

On the other side, virtually 100% of the oxygen they add to sea water is being used by their partners to oxidize iron.

On the top side, they could put out enough oxygen to cause the GREAT OXIDATION of labile reductants on the lifeless land above sea level.

On the bottom side, they weren't making a dent in the ocean's total ferrous iron supply.

They were already putting enough oxygen into the atmosphere to change the chemistry of the land.

It would be another... 900 million years?

Well, it was going to take a LONG time before any free oxygen could be found in sea water. There was just too much ferrous iron to rust away first.

Im a BM wrote:
The Great Oxidation 2450 Million Years Ago

About 2450 million years ago, oxygen became available to the atmosphere.

While it would not have created more than low single digit percentage concentration in the atmosphere, it brought about the oxidation of labile reductants on the land above sea level.

This, in turn, created many new niches for life to live outside of the sea.

Bacteria could not live on the upland surface because the intensity of ultraviolet light would have fried them.

But dozens of new niches opened up underground.

Using atmospheric oxygen, bacteria could acquire energy through the oxidation of dozens of different reductants.

Ferrous iron(II), manganese(II), sulfides, arsenic(III), phosphorus(III), boron, reduced forms of selenium, vanadium, molybdenum, ammonium, nitrite... and the list goes on and on.

ALL of them could be oxidized for energy yield using oxygen as terminal electron acceptor.

Bacteria evolved to use many many reductants.

Some, such as sulfides could give a LOT of bang for the buck when coupled to an oxidant as powerful as oxygen.

Others, such as nitrite, don't give much bang for the buck. But before oxygen came along, there were no oxidants powerful enough to oxidize nitrite for any kind of energy payoff.

Damp underground flow paths came to support ENORMOUS biomass of chemoautotrophs on the land above sea level.

Downstream, submarine groundwater discharge began to bring in all kinds of new terminal electron acceptors into the sea.

The oxygen enabled great oxidation all right.

The oxidized products - the sulfate, nitrate, arsenate, manganese(IV), ferric iron(III), borate, molybdate, selenate, phosphate, vanadate, etc. etc. were now available for use as terminal electron acceptors.

The sea floor organic carbon was going to take a beating. And every single one of those terminal electron acceptors yields CARBONATE rather than carbon dioxide as the inorganic carbon product of oxidation. Along with insoluble products of reduction, such as iron pyrite.

sealover wrote:
I wish Hans Jenny were still alive so I could share this with him. It is kind of like "state factors" of soil formation applied to the genesis of banded iron formation.


What is actually NEW and DIFFERENT about this model for the genesis of banded iron formations?

The INTRACELLULAR PHOTOOXIDATION hypothesis as the explanation for the origin of photosynthesis.

Photosynthesis takes in reductants from the environment and, via intracellular photooxidation, generates oxidized waste products - oxygen, nitrate, ferric iron(III), arsenic(V) arsenate, sulfate, or water. It originally evolved as a way to the exploit energy rich reductant, hydrogen, readily available from the environment. And to do so despite the scarcity of terminal electron acceptors (oxidants) available in the water.

The EXPANDING PHOTOSYSTEM OXIDATION CAPACITY hypothesis as the explanation for how anoxygenic photosynthetic bacteria were able to exploit reductants WEAKER than hydrogen, readily available in the environment

The first photosynthetic bacteria exploited the energy from hydrogen available in the environment by employing intracellular photooxidation. An atom such as manganese could be photooxidized within the cell, from manganese(II) to manganese(IV). Manganese(IV) acts as terminal electron acceptor to oxidize the hydrogen and become manganese(II) again. Photooxidize and repeat.

The first photosystem employed low end ultraviolet light using only the most rudimentary light harvesting apparatus. Low end UV could not penetrate very deeply into the hydrogen rich water. To exploit the hydrogen beyond the shallowest water, the light harvesting apparatus expanded to be able to use light of longer wavelenths for intracellular photooxidation. Blue light and even red light. The same expansion photosystem oxidation capacity to use high energy reductant in low light would eventually make it possible to exploit low energy reductants in high light.

The RHYHMICALLY VIBRATING CRUST hypothesis as the explanation for the consistent intervals in the spacing of "microbanded" banded iron formations, the most ancient of them all.

4000 million years ago the Earth's crust was thin and flexible, belching out gas and steam on a frequent, regular schedule. Like the Old Faithful geyser at Yellowstone, with bursts of gas and steam coming out with a consistent rhythm. The microbanded layers were once called "annual varves" because the uncanny regularity of the spacing suggested a regular annual cycle, over many years.

Reductant rich steam pulsed through the Earth's veins underneath its thin skin. The pace of the Earth's heart beat 4000 million years ago is recorded in the spacing between between the layers of the microbanded iron formations.

The SEQUENTIAL REDUCTANT DEPLETION hypothesis as the explanation for the sequence of photosynthetic community succession recorded in the banded iron formations.

As hydrogen gas from the most recent burst of geothermal activity floated off into outer space, its concentration rapidly diminished in sea water. The hydrogen gravy train was a short lived ride. While it was there, anoxygenic photosynthetic bacteria using hydrogen as reductant had the competitive advantage, using the strongest available reductant.

After a time, following the cessation of vulcanism, hydrogen is too depleted to support them anymore, so the competitive advantage goes to the photosynthetic community that can use the next strongest reductant - hydrogen sulfide. And so on, when the sulfide is depleted, the next strongest reductant will be selectively consumed from the water by photosynthetic bacteria.

The PHOTOSYNTHETIC COMMUNITY SUCCESSION hypothesis as the explanation for the chemistry of the banded iron formations.

The first wave of photosynthetic community succession were the bacteria that could use hydrogen as reductant for photosynthesis. They got the most bang for the buck from sunlight and could outgrow competitors who used any other reductant. Using hydrogen as reductant, the oxidized waste product of photosynthesis is water.

This highly productive photosynthetic community rained organic carbon down to the sea floor. There were very few terminal electrons acceptors around to use to oxidize organic carbon. And photosynthesis wasn't producing any oxidants. Pure organic carbon material remained on the sea floor unoxidized. It later fossilized into pure chert as all the organic carbon was replaced by silica.

The next community in the succession, after hydrogen was depleted left a very different chemical fingerprint on the sea floor. Sulfur based anoxygenic photosynthesis generates sulfate as the oxidized product. Sulfate can be used as a terminal electron acceptor by bacteria to oxidize organic carbon. Sulfate reduction transforms organic carbon into inorganic carbon, as carbonate. It also produces iron pyrite while its at it.

This photosynthetic community rained organic carbon on to the sea floor, but it also put sulfate in the water, which led to the formation of iron pyrite and carbonate in the sea floor. This would NOT fossilize into pure chert. And so on with each successive photosynthetic community, putting out a different oxidized product from its photosynthesis, leaving its unique chemical fingerprint in the sea floor.

The SYMBIOTIC ALLELOPATHIC OXIDATION hypothesis as the explanation for the ability of cyanobacteria to dominate a narrow zone at the surface while anoxygenic photosynthesis was excluded to the shade beneath them.

With so much ferrous iron in sea water at the time, cyanobacteria couldn't possibly compete with the iron based anoxygenic photosynthetic bacteria. Cyanobacteria just couldn't get as much bang for the buck from sunlight.

Cyanobacteria partnered with iron oxidizing bacteria, to whom they provided exclusive access to the strong oxidant the generated as waste product. A very thin layer of them on the surface could create an exclusion zone depleted of ferrous iron. Their faster growing competitors couldn't compete at all without enough ferrous iron in the water. Unlike ferrous iron, ferric iron is insoluble in sea water, so it precipitated out of solution and fell to the sea floor.

The iron based photosynthetic bacteria back then had to do what they do today where ferrous iron seeps up from the sea floor. They have to live in the shade beneath the oxygenic photosynthetic community.

The GREAT OXIDATION was facilitated by a thin mat of cyanobacteria dominating the high light zone at the sea water surface. At the same time the cyanobacteria mat dumped ferric iron on the sea floor, it blasted oxygen up into the atmosphere.

I wasn't enough to bring the atmosphere to anything higher than low single digit percentages of oxygen, but it faciliated the oxidation of labile reductants in the continent(s). The lifeless continents would become home to enormous biomass of underground chemoautotrophic bacteria. The presence of even very low concentrations of oxygen in the atmosphere opened up dozens of niches for bacteria to use dozens of different reductants.

As atmospheric oxygen supported the great oxidation of the minerals along the underground flow paths of the continents, it began to supply a wide variety of terminal electron acceptors to the sea that could be used by bacteria to oxidize the organic carbon of the sea floor. Arsenate, borate, phosphate, selenate, molybdate, selenate, vanadate, nitrate,.. and the list goes on. The sea floor organic carbon would now be subjected to oxidation by a wild mix of terminal electron acceptors of varying strength.

There was enough oxygen in the atmosphere to cause big chemical changes to the continents.

But there was SO DAMN MUCH ferrous iron in the sea water, it would take nearly 1000 million more years of cyanobacteria on the surface mat producing oxygen before the ferrous iron all got oxidized. FINALLY it would be possible for there to be enough free oxygen in sea water support the Cambrian Explosion.

sealover wrote:
I had the incredible honor of knowing Dr. Hans Jenny when I was at UC Berkeley.

He was to soil science what Darwin was to biology. What Newton was to physics. What Pasteur was to medical science. A giant.

He helped a lot of farmers by figuring out that dry ammonia could be adsorbed to the soil.

He helped a lot of soil scientists understand the thermodynamically predictable properties that soils acquire under the influence of quantifiable state factors.

I wish Hans Jenny were still alive so I could share this with him. It is kind of like "state factors" of soil formation applied to the genesis of banded iron formation.

My next step right now for this is to try to pull a Hans Jenny with the banded iron formations.

Banded iron formations have thermodynamically predictable properties acquired under the influence of quantifiable state factors.

For soil, Hans Jenny noticed that ORGANISMS play a pretty important role.

Obviously, the presence or absence of living organisms would be an important state factor to consider in the genesis of banded iron formations.

Who was there to synthesize organic carbon?

Who was there to oxidize organic carbon?

For soil, Hans Jenny noticed that the physical and chemical properties of the soil PARENT MATERIAL were an important state factor to consider.

The parent material for banded iron formations is sea water.

Which reductants were present? How much?

Which terminal electron acceptors were present? How much?

What are the thermodynamically predictable properties that will be found in the sediment deposited with such organisms present or absent, with such reductants present or absent, or with such terminal electron acceptors present or absent?

I think it would PREDICT what you should find in the different layers of the banded iron formations.


What is actually NEW and DIFFERENT about this model for the genesis of banded iron formations?

The INTRACELLULAR PHOTOOXIDATION hypothesis as the explanation for the origin of photosynthesis.

Photosynthesis takes in reductants from the environment and, via intracellular photooxidation, generates oxidized waste products - oxygen, nitrate, ferric iron(III), arsenic(V) arsenate, sulfate, or water. It originally evolved as a way to the exploit energy rich reductant, hydrogen, readily available from the environment. And to do so despite the scarcity of terminal electron acceptors (oxidants) available in the water.

The EXPANDING PHOTOSYSTEM OXIDATION CAPACITY hypothesis as the explanation for how anoxygenic photosynthetic bacteria were able to exploit reductants WEAKER than hydrogen, readily available in the environment

The first photosynthetic bacteria exploited the energy from hydrogen available in the environment by employing intracellular photooxidation. An atom such as manganese could be photooxidized within the cell, from manganese(II) to manganese(IV). Manganese(IV) acts as terminal electron acceptor to oxidize the hydrogen and become manganese(II) again. Photooxidize and repeat.

The first photosystem employed low end ultraviolet light using only the most rudimentary light harvesting apparatus. Low end UV could not penetrate very deeply into the hydrogen rich water. To exploit the hydrogen beyond the shallowest water, the light harvesting apparatus expanded to be able to use light of longer wavelenths for intracellular photooxidation. Blue light and even red light. The same expansion photosystem oxidation capacity to use high energy reductant in low light would eventually make it possible to exploit low energy reductants in high light.

The RHYHMICALLY VIBRATING CRUST hypothesis as the explanation for the consistent intervals in the spacing of "microbanded" banded iron formations, the most ancient of them all.

4000 million years ago the Earth's crust was thin and flexible, belching out gas and steam on a frequent, regular schedule. Like the Old Faithful geyser at Yellowstone, with bursts of gas and steam coming out with a consistent rhythm. The microbanded layers were once called "annual varves" because the uncanny regularity of the spacing suggested a regular annual cycle, over many years.

Reductant rich steam pulsed through the Earth's veins underneath its thin skin. The pace of the Earth's heart beat 4000 million years ago is recorded in the spacing between between the layers of the microbanded iron formations.

The SEQUENTIAL REDUCTANT DEPLETION hypothesis as the explanation for the sequence of photosynthetic community succession recorded in the banded iron formations.

As hydrogen gas from the most recent burst of geothermal activity floated off into outer space, its concentration rapidly diminished in sea water. The hydrogen gravy train was a short lived ride. While it was there, anoxygenic photosynthetic bacteria using hydrogen as reductant had the competitive advantage, using the strongest available reductant.

After a time, following the cessation of vulcanism, hydrogen is too depleted to support them anymore, so the competitive advantage goes to the photosynthetic community that can use the next strongest reductant - hydrogen sulfide. And so on, when the sulfide is depleted, the next strongest reductant will be selectively consumed from the water by photosynthetic bacteria.

The PHOTOSYNTHETIC COMMUNITY SUCCESSION hypothesis as the explanation for the chemistry of the banded iron formations.

The first wave of photosynthetic community succession were the bacteria that could use hydrogen as reductant for photosynthesis. They got the most bang for the buck from sunlight and could outgrow competitors who used any other reductant. Using hydrogen as reductant, the oxidized waste product of photosynthesis is water.

This highly productive photosynthetic community rained organic carbon down to the sea floor. There were very few terminal electrons acceptors around to use to oxidize organic carbon. And photosynthesis wasn't producing any oxidants. Pure organic carbon material remained on the sea floor unoxidized. It later fossilized into pure chert as all the organic carbon was replaced by silica.

The next community in the succession, after hydrogen was depleted left a very different chemical fingerprint on the sea floor. Sulfur based anoxygenic photosynthesis generates sulfate as the oxidized product. Sulfate can be used as a terminal electron acceptor by bacteria to oxidize organic carbon. Sulfate reduction transforms organic carbon into inorganic carbon, as carbonate. It also produces iron pyrite while its at it.

This photosynthetic community rained organic carbon on to the sea floor, but it also put sulfate in the water, which led to the formation of iron pyrite and carbonate in the sea floor. This would NOT fossilize into pure chert. And so on with each successive photosynthetic community, putting out a different oxidized product from its photosynthesis, leaving its unique chemical fingerprint in the sea floor.

The SYMBIOTIC ALLELOPATHIC OXIDATION hypothesis as the explanation for the ability of cyanobacteria to dominate a narrow zone at the surface while anoxygenic photosynthesis was excluded to the shade beneath them.

With so much ferrous iron in sea water at the time, cyanobacteria couldn't possibly compete with the iron based anoxygenic photosynthetic bacteria. Cyanobacteria just couldn't get as much bang for the buck from sunlight.

Cyanobacteria partnered with iron oxidizing bacteria, to whom they provided exclusive access to the strong oxidant the generated as waste product. A very thin layer of them on the surface could create an exclusion zone depleted of ferrous iron. Their faster growing competitors couldn't compete at all without enough ferrous iron in the water. Unlike ferrous iron, ferric iron is insoluble in sea water, so it precipitated out of solution and fell to the sea floor.

The iron based photosynthetic bacteria back then had to do what they do today where ferrous iron seeps up from the sea floor. They have to live in the shade beneath the oxygenic photosynthetic community.

The GREAT OXIDATION was facilitated by a thin mat of cyanobacteria dominating the high light zone at the sea water surface. At the same time the cyanobacteria mat dumped ferric iron on the sea floor, it blasted oxygen up into the atmosphere.

I wasn't enough to bring the atmosphere to anything higher than low single digit percentages of oxygen, but it faciliated the oxidation of labile reductants in the continent(s). The lifeless continents would become home to enormous biomass of underground chemoautotrophic bacteria. The presence of even very low concentrations of oxygen in the atmosphere opened up dozens of niches for bacteria to use dozens of different reductants.

As atmospheric oxygen supported the great oxidation of the minerals along the underground flow paths of the continents, it began to supply a wide variety of terminal electron acceptors to the sea that could be used by bacteria to oxidize the organic carbon of the sea floor. Arsenate, borate, phosphate, selenate, molybdate, selenate, vanadate, nitrate,.. and the list goes on. The sea floor organic carbon would now be subjected to oxidation by a wild mix of terminal electron acceptors of varying strength.

There was enough oxygen in the atmosphere to cause big chemical changes to the continents.

But there was SO DAMN MUCH ferrous iron in the sea water, it would take nearly 1000 million more years of cyanobacteria on the surface mat producing oxygen before the ferrous iron all got oxidized. FINALLY it would be possible for there to be enough free oxygen in sea water support the Cambrian Explosion.