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PetTastic
2014-Feb-22, 06:09 PM
On Earth, we have microbes that obtain their energy from reducing sulphates with hydrogen.
http://en.wikipedia.org/wiki/Sulfate-reducing_bacteria

On planets with hydrogen dominated atmospheres what direction could evolution take?
Without free oxygen would food chains develop? Or instead would all life derive its energy directly from hydrogen and sulphates?

Would the hunt for hydrogen and sulphate minerals be enough to drive evolution of higher life-forms?
Or maybe the evolution of oxygen producing life-forms is inevitable.

Noclevername
2014-Feb-22, 06:14 PM
Without free oxygen would food chains develop?

Food chains IIRC existed during the 3 billion or so years that Earth had little free oxygen, and exist among anaerobes today, so I'm guessing yes.


On planets with hydrogen dominated atmospheres what direction could evolution take?

Would the hunt for hydrogen and sulphate minerals be enough to drive evolution of higher life-forms?

Or maybe the evolution of oxygen producing life-forms is inevitable.


These questions can't be answered without finding a planet with only anaerobic hydrogen-using life.

Colin Robinson
2014-Feb-22, 10:08 PM
On Earth, we have microbes that obtain their energy from reducing sulphates with hydrogen.
http://en.wikipedia.org/wiki/Sulfate-reducing_bacteria

On planets with hydrogen dominated atmospheres what direction could evolution take?
Without free oxygen would food chains develop? Or instead would all life derive its energy directly from hydrogen and sulphates?

Would the hunt for hydrogen and sulphate minerals be enough to drive evolution of higher life-forms?
Or maybe the evolution of oxygen producing life-forms is inevitable.

Sulfates are highly oxidized compounds, hence less likely to be found on a planet with a hydrogen-dominated (reducing) atmosphere, than on a planet with an oxygen-dominated (oxidizing) atmosphere such as Earth.

But sulfates are not the only compounds from which energy can be obtained via a reaction with hydrogen.

The reaction between hydrogen and carbon dioxide, producing methane plus water, also releases energy. This reaction is used by another class of microbes (methanogens) on Earth.

Energy can also be derived from the reaction between hydrogen and acetylene, and this has been suggested as a possible energy source for organisms on Titan.

To work out a plausible scenario for evolution in a hydrogen-dominated atmosphere, you'd need to look specifically at what else is present apart from hydrogen. You'd also have to quantify how much energy the possible exothermic reactions provide. Or in the case of endothermic reactions, how much energy they require.

PetTastic
2014-Feb-22, 10:53 PM
Food chains IIRC existed during the 3 billion or so years that Earth had little free oxygen, and exist among anaerobes today, so I'm guessing yes.

The thing is oxygen producing organisms have been pumping oxygen into shallow seas for 3.5 billion years.
So the oxygen levels in these seas could have been high enough for oxygen to be used to metabolise food.



These questions can't be answered without finding a planet with only anaerobic hydrogen-using life.

Yes, but what would we be looking for out there?
What tell-tale waste products in the atmosphere, or in water under ice would we be looking for?

PetTastic
2014-Feb-22, 11:13 PM
Energy can also be derived from the reaction between hydrogen and acetylene, and this has been suggested as a possible energy source for organisms on Titan.

To work out a plausible scenario for evolution in a hydrogen-dominated atmosphere, you'd need to look specifically at what else is present apart from hydrogen. You'd also have to quantify how much energy the possible exothermic reactions provide. Or in the case of endothermic reactions, how much energy they require.

There just seems so many possibilities that to me, it seems an oxygen atmosphere like ours is improbable.
If the Earth's ammonia methane atmosphere had not been bombarded by comets bring water, then this planet could have been hydrogen dominated.
Assuming most of the original oxygen is locked in rock minerals.
In a hydrogen environment would plants release any oxygen they produced. It would be a high-energy food they could combine with hydrogen for energy? (Is this how thing started here?)

What kinds of food could you extract from other creatures and metabolise using hydrogen?

eburacum45
2014-Feb-22, 11:43 PM
Here are Carl Sagan and E E Salpeter's ideas on an ecology in a gas giant
http://articles.adsabs.harvard.edu/cgi-bin/nph-iarticle_query?1976ApJS...32..737S&data_type=PDF_H IGH&whole_paper=YES&type=PRINTER&filetype=.pdf

The Earth's first atmosphere probably did consist of hydrogen and helium, but this was soon lost - out planet can't hold onto light gases like H2 and He for very long.

cjameshuff
2014-Feb-23, 04:12 AM
There just seems so many possibilities that to me, it seems an oxygen atmosphere like ours is improbable.
If the Earth's ammonia methane atmosphere had not been bombarded by comets bring water, then this planet could have been hydrogen dominated.
Assuming most of the original oxygen is locked in rock minerals.

How would arrival of water cause hydrogen to go away? How do you keep the hydrogen from reacting with oxygen in rocks or CO2?

A terrestrial world is not likely to have a hydrogen atmosphere. Hydrogen is too reactive and escapes too easily, oxygen is too common...a third of Earth's mass is oxygen. What doesn't react would be quickly lost due to the lack of a gravity well sufficient to hold onto it...with a bad end for any world taken over by life that produces large quantities of hydrogen from water. Only planets with an overwhelming excess of hydrogen (gas giants) are likely to have hydrogen-rich atmospheres.

For stuff that's stable and inert enough to form the bulk of a permanent atmosphere on a terrestrial world, you're pretty much stuck with CO2 and N2. Given a warm terrestrial world with a CO2 and N2 atmosphere, production of O2 by life is certainly not far-fetched...CO2 is a biologically useful source of carbon, and that leaves an excess of oxygen to get rid of. So what's improbable about our atmosphere?



In a hydrogen environment would plants release any oxygen they produced. It would be a high-energy food they could combine with hydrogen for energy? (Is this how thing started here?)

Prior to large amounts of oxygen accumulating in the environment, this was the case...oxygen could potentially be combined with the sugars produced by photosynthesis to yield energy. Oxygen was released anyway. It's not so easy to store, storage wouldn't give a benefit until there was the ability to use it, and its reactivity makes it fairly toxic.

Colin Robinson
2014-Feb-23, 04:53 AM
There just seems so many possibilities that to me, it seems an oxygen atmosphere like ours is improbable.
If the Earth's ammonia methane atmosphere had not been bombarded by comets bring water, then this planet could have been hydrogen dominated.
Assuming most of the original oxygen is locked in rock minerals.
In a hydrogen environment would plants release any oxygen they produced. It would be a high-energy food they could combine with hydrogen for energy? (Is this how thing started here?)

In a hydrogen-rich (reducing) environment, I don't think plants would produce oxygen.

Plants on Earth today produce oxygen, as waste product, because they use the water molecule as a reducing agent, i.e. as a hydrogen source.

But would it make evolutionary sense to use water as a reducing element if free hydrogen was available in the atmosphere? The thing is, if you use free hydrogen as a reducing agent (e.g. by combining it with sulfates, or with carbon dioxide), you release useful energy. By contrast, if you use water as a reducing element, you need to input energy (i.e. the reaction is endothermic).

So it would only make evolutionary sense to use water as a reducing element on a world with plenty of water and very little free hydrogen.


(Is this how thing started here?)

I think the geological evidence (as well as the logic of thermodynamics) says that on Earth plants (or, strictly speaking, photosynthesizing microbes) began to produce oxygen molecules at a time when nearly all of the hydrogen atoms in the atmosphere were contained in water molecules.

In other words, before photosynthesis changed things, Earth's atmosphere was neither oxygen-rich nor hydrogen-rich — it contained hardly any free oxygen (O2) and hardly any free hydrogen (H2). But plenty of H2O and CO2.


What kinds of food could you extract from other creatures and metabolise using hydrogen?

Just about any organic compound you extracted from other creatures (as long as the organic compound was more complex than methane) could be hydrogenated into methane and other simple molecules, releasing energy. Not necessarily as much energy as you get by using oxygen, though.

cjameshuff
2014-Feb-23, 01:06 PM
In a hydrogen-rich (reducing) environment, I don't think plants would produce oxygen.

Plants on Earth today produce oxygen, as waste product, because they use the water molecule as a reducing agent, i.e. as a hydrogen source.

But would it make evolutionary sense to use water as a reducing element if free hydrogen was available in the atmosphere? The thing is, if you use free hydrogen as a reducing agent (e.g. by combining it with sulfates, or with carbon dioxide), you release useful energy. By contrast, if you use water as a reducing element, you need to input energy (i.e. the reaction is endothermic).

So it would only make evolutionary sense to use water as a reducing element on a world with plenty of water and very little free hydrogen.

Again, large amounts of hydrogen won't stick around. It'll combine with something or escape the atmosphere. If Earth ever had a hydrogen atmosphere, it was only for a very brief time. The permanent atmosphere would likely be stuff that outgasses from volcanism: mainly CO2, H2O, and N2, the original CH4 and NH3 decomposing quickly and the resulting C and H combining with the extremely abundant (again, one third of Earth's mass) oxygen.

And yes, you need to input energy to combine CO2 and H2O. That's how photosynthesis works and why it provides a survival advantage: it lets organisms tap sources of energy other than ambient chemicals.



I think the geological evidence (as well as the logic of thermodynamics) says that on Earth plants (or, strictly speaking, photosynthesizing microbes) began to produce oxygen molecules at a time when nearly all of the hydrogen atoms in the atmosphere were contained in water molecules.

Geological evidence says the atmosphere has largely remained the same, apart from becoming oxygenated at one point. There's no sign it was ever strongly reducing (which a hydrogen atmosphere would be).
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2944365/

Colin Robinson
2014-Feb-23, 06:33 PM
A terrestrial world is not likely to have a hydrogen atmosphere.

Did the question in the OP specify that the planet with a hydrogen dominated atmosphere would have to be a "terrestrial" one?


Hydrogen is too reactive and escapes too easily, oxygen is too common...

Is hydrogen more reactive than oxygen? Which of these two elements is cosmically more common?


What doesn't react would be quickly lost due to the lack of a gravity well sufficient to hold onto it...

That depends on the how much gravity the planet has, and on the amount of radiation hitting its upper atmosphere.


Only planets with an overwhelming excess of hydrogen (gas giants) are likely to have hydrogen-rich atmospheres.

Well, Titan is not a gas giant, it's a planet-sized moon with significant amounts of H2 in its atmosphere.

Colin Robinson
2014-Feb-23, 06:45 PM
And yes, you need to input energy to combine CO2 and H2O. That's how photosynthesis works and why it provides a survival advantage: it lets organisms tap sources of energy other than ambient chemicals.

But would photosynthesis (as performed on Earth) provide an evolutionary advantage on a planet with significant H2 in its atmosphere?

PetTastic
2014-Feb-23, 10:58 PM
On Earth Venus and Mars, hydrogen is being lost to the solar wind, but it seems quite tricky to work out the rate this happened in the past.
Some recent papers have given very different estimates of how strong the Sun's winds were in the past.
newscientist (http://www.newscientist.com/article/mg22129542.800-did-newborn-sun-have-weirdly-weak-solar-wind.html#.Uwp2MIVwTnE)

One interesting problem for photosynthesis seems to be the availability of CO2 in a hydrogen atmosphere.
In a star forming nebula, the most common molecular gasses are hydrogen and carbon monoxide, most of the solid material has been soaked in hot ionize hydrogen for millions of years before the planet formed.

So my guess at the planet's original atmosphere, is more like hydrogen, carbon monoxide, ammonia, water, methane.
The planets surface being heavily made from highly reducing exotic compounds. Many of these would spontaneously combust in an oxygen atmosphere.
As a result, most carbon dioxide present on a primitive planet, delivered by comets as dry ice, would be reduced to CO by all the exotic compounds, nitrides, hydrides, alluminum etc. etc.

I have been looking at the chemistry for replenishing sulphates and other oxidised compounds that could fuel hydrogen breathers.
I spotted one odd reaction that has potential. The production of O3 and nitrogen oxides by the action of UV light on carbon monoxide in smog.
It looks 'possible' to produce sulpuric acid rain and hence sulphates via this route.

Colin Robinson
2014-Feb-24, 09:08 AM
On Earth Venus and Mars, hydrogen is being lost to the solar wind, but it seems quite tricky to work out the rate this happened in the past.
Some recent papers have given very different estimates of how strong the Sun's winds were in the past.
newscientist (http://www.newscientist.com/article/mg22129542.800-did-newborn-sun-have-weirdly-weak-solar-wind.html#.Uwp2MIVwTnE)

One interesting problem for photosynthesis seems to be the availability of CO2 in a hydrogen atmosphere.
In a star forming nebula, the most common molecular gasses are hydrogen and carbon monoxide, most of the solid material has been soaked in hot ionize hydrogen for millions of years before the planet formed.

So my guess at the planet's original atmosphere, is more like hydrogen, carbon monoxide, ammonia, water, methane.
The planets surface being heavily made from highly reducing exotic compounds. Many of these would spontaneously combust in an oxygen atmosphere.
As a result, most carbon dioxide present on a primitive planet, delivered by comets as dry ice, would be reduced to CO by all the exotic compounds, nitrides, hydrides, alluminum etc. etc.

I think it would depend on how hydrogen-dominated (how reducing) the atmosphere was. CO2 could get reduced to CO, or could get reduced all the way to methane (CH4).

Although lack of carbon dioxide would rule out the form of photosynthesis most familiar to us on Earth, it would not rule out photosynthesis in the generic sense of complex organics getting synthesized (i.e. formed out of simpler molecules) with the help of an input of solar energy.


I have been looking at the chemistry for replenishing sulphates and other oxidised compounds that could fuel hydrogen breathers.
I spotted one odd reaction that has potential. The production of O3 and nitrogen oxides by the action of UV light on carbon monoxide in smog.
It looks 'possible' to produce sulpuric acid rain and hence sulphates via this route.

Doesn't O3 production require O2 in the atmosphere as well as CO?

PetTastic
2014-Feb-24, 04:38 PM
I think it would depend on how hydrogen-dominated (how reducing) the atmosphere was. CO2 could get reduced to CO, or could get reduced all the way to methane (CH4).
My guess is early in our star system existence, before the planets were created, the proto planetary material became heavily depleted in hydrogen as part of the star forming process.
Otherwise, volcanoes would have been blasting out CO, hydrogen and nitrogen for most of the Earth early life.

If this is common, then it reduces the chances of finding hydrogen dominated planets in a habitable zone. (Habbitable for hydrogen breathers?)


Although lack of carbon dioxide would rule out the form of photosynthesis most familiar to us on Earth, it would not rule out photosynthesis in the generic sense of complex organics getting synthesized (i.e. formed out of simpler molecules) with the help of an input of solar energy.
I suspect there are many ways organisms can gain energy from light.
It is just that here the carbon dioxide is the source of the oxygen.



Doesn't O3 production require O2 in the atmosphere as well as CO?
I was looking at the first part of this reaction
http://en.wikipedia.org/wiki/Tropospheric_ozone#Formation
UV + water + carbon monoxide -> HO+ ions.
I was thinking combining the HO+ with water and sulphur dioxide, might do the trick, making sulphuric acid and therefor sulphates.

Colin Robinson
2014-Feb-25, 08:50 AM
My guess is early in our star system existence, before the planets were created, the proto planetary material became heavily depleted in hydrogen as part of the star forming process.
Otherwise, volcanoes would have been blasting out CO, hydrogen and nitrogen for most of the Earth early life.

If this is common, then it reduces the chances of finding hydrogen dominated planets in a habitable zone. (Habbitable for hydrogen breathers?)

There are a lot of unanswered questions about what sorts of planets/moons could support life. E.g. Does it require stable bodies of liquid surface water? Or can subsurface water support life? Or surface bodies of another liquid (e.g. Titan's hydrocarbon lakes)?

Even if habitability does require liquid surface water, that might be still be feasible on a "super-Earth" in the outer part of its system — i.e. a body somewhat more massive than Earth, though not in the gas giant class, situated in a region of its solar system that was comparable to the hydrogen-rich outer region of our own solar system.

The surface of such an "outer super-Earth" could have an Earth-like temperature due to the green-house effects of a comparatively thick atmosphere.


I suspect there are many ways organisms can gain energy from light.
It is just that here the carbon dioxide is the source of the oxygen.

One way a light-using organism on a hydrogen-rich world could turn light energy in chemical energy, would be to use water as an oxidizing agent. The process wouldn't require CO2 as an input, it would get carbon from methane or some other hydrogen-rich carbon compound.

The chemistry of this oxidization process would be in some ways like photosynthesis on Earth (because energy from light would be used to break up the water molecule) yet it would also be in some ways similar to respiration on Earth (because hydrogen-rich carbon compounds were being turned step-by-step into oxygen-rich ones).

It would be similar in principle to something you suggested earlier in this thread -- plants storing oxygen as valuable fuel -- except that they wouldn't be storing O2 molecules as such, they would be storing oxygen atoms as an energy-providing component within organic molecules.


I was looking at the first part of this reaction
http://en.wikipedia.org/wiki/Tropospheric_ozone#Formation
UV + water + carbon monoxide -> HO+ ions.
I was thinking combining the HO+ with water and sulphur dioxide, might do the trick, making sulphuric acid and therefor sulphates.

??

I had a look at the article, couldn't see where it mentions "HO+ ions".

PetTastic
2014-Feb-25, 11:41 AM
??

I had a look at the article, couldn't see where it mentions "HO+ ions".

Oops that was a typo followed by a block copy of typo.

That should be hydroxyl HO or hydroxyl ions HO-.
The idea being these would be attracted to water droplets producing a locally oxidising environment inside them via H2O2.
This could possibly oxidise Sulfurous acid to Sulphric acid.
It sounds just about plausable to me.

The evolutionary route to higher life-forms also seems a bit iffy.
The only thing I can think of, is that if sulphates are scarce, then there could be evolutionary pressure toward mobility.
Then if you need to mine the stuff, possible incentive for tool use?
Then there would be a great advantage in going toward chemical production of sulphates.

Nick Theodorakis
2014-Feb-25, 01:33 PM
But would photosynthesis (as performed on Earth) provide an evolutionary advantage on a planet with significant H2 in its atmosphere?

There are bacteria that perform anoxygenic photosythesis and some of them use hydrogen. Others use sulfur or hydrogen sulfide. It's thought that this type of photosynthesis preceded the oxygen-producing type.

Nick

Colin Robinson
2014-Feb-26, 11:42 PM
There are bacteria that perform anoxygenic photosythesis and some of them use hydrogen. Others use sulfur or hydrogen sulfide. It's thought that this type of photosynthesis preceded the oxygen-producing type.

Nick

When organisms use free hydrogen molecules to hydrogenate CO2, logically that is chemosynthesis rather than photosynthesis, because the reaction is exothermic — no input of light energy required.