It seems we are getting closer and closer to find earth size planets in other solar systems. The next step is to find the chemical make-up of the atmospheres. The question is, if you find oxygen in a concentration greater than 10% on a planet does that mean there is life there? Seems pretty cool to even find a water/nitrogen planet or something close.

No.

Perhaps more interesting would be if such a finding raises the probability of finding life there, or if the lack of such a finding reduces the probability. However, I do not have answers to these questions.

A planet or moon covered with water ice (e.g. Jupiter's moons) might have close to 100% Oxygen atmosphere. Basically water vapour splits light hydrogen leaves heavy oxygen stays behind. But with no liquid water life is unlikely.

(Nether the less Jupiters moons are still our best shot for large multi-celled life forms in this solar system.)

couldn't a planet have enough oxygen and not have any liquid water?

Not sure what you mean. However it is liquid water that is usually considered essential for life (as least as we know it). Oxygen is not essential, there are plenty of living organisms that do not need oxygen.

There was very little oxygen in the atmosphere when life first developed on Earth, it was life coevolving with the atmosphere that put the oxygen in the atmosphere.

I think the point is that oxygen in the atmosphere is usually associated with large deposits of H2O. If the temperature is suitable for liquid water than life would appear likely.

An Oxygen atmosphere is neither necessary nor sufficient for life, but it is a hypothesiseable that oxygen in the atmosphere increases the chance of life being present. But we have insufficent data to test this.

I think there is absolutely no reason there needs to be some minimal level of O2 for life. One of the major transitions in evolution was the development of mechanisms to detoxify oxygen. It's likely that atmospheric O2 above some level (I dunno, 50%) would be too reactive and things would be on fire for the most part.

And I think that is the interesting point.

Is it likely for a planet of earth-like properties (size, temperature range) to have large concentrations of oxygen in the atmosphere without biological processes?

A planet in the goldilox zone with that much atmospheric oxygen would be strong enough evidence to justify building an photo inferometer to image its surface.

Maybe. My hunch would no. But it is perilous to make such assumptions in advance of the data to back them up.

How many really plausible looking theories have been show false once sufficient data had been collected.

That is what I am thinking too. Oxygen is an somewhat unstable compound. Without biological processes on earth, our atmosphere would be carbon dioxide, nitrogen and water vapor. In a water world, it would probably be 99% nitrogen as the co2 would mostly dissolve in the oceans. It might be safe to visit these planets with only a oxygen mask and no suit, if they have a magnetic field. Might be easy to terraform, with solar power converting h2o to h2 and o2 and sending the h2 into space.

forum has deteriorated

Curt responses probably

This imo.

I actually agree...

If you don't understand the science threads, you are allowed to not post in them.

CO2 > O2

oxygen is likely the enemy of the formation of life

was a typo in the question, not sure how the word enough got into the sentence it doesn't even make sense.

what I mean is can a planet have oxygen without having water? lets assume its a rocky planet the same size as ours, it has loads of hydrogen and oxygen what conditions would be required to stop water (ice or liquid) from forming? I'd guess excessive heat would be one thing but how hot would it have to be?
what about other chemicals in the atmosphere? what does oxygen like to bond most with? (is there even such a thing?)

That's not the point. There doesn't seem to be a chemical process that would have created the concentration of oxygen in earth's atmosphere. It was created mostly by life forms (i.e., plants).

Therefore, the theory goes, detecting similar concentrations of O2 on a similar planet would imply a biological process.

I think Venus lost its water from losing hydrogen to space, leaving o2. Which might happen to this planet, i think we lose 3 kg a second of hydrogen to space coming from water. But, I still think if you find o2 at 10% it might prove life. So rather than sending man to Mars looking for life, it might be better to send large telescopes out searching for oxygen.

The "O2" in venus's atmosphere is "CO2".

http://www.vanderbilt.edu/AnS/physic..._on_venus.html

From this link.

# solar UV busts apart the water molecule into its constituent atoms;
# the lightweight hydrogen atom bubbles up to the top of the atmosphere and escapes;
# the oxygen rusts (oxydizes) surface rocks;


Either way, tectonic activity begins to slow down. The higher temperature drives more water into the atmosphere. The added water vapor pressure drives more CO2 out of the oceans and into the atmosphere. The added H2O and CO2 in the atmosphere increase the greenhouse effect. The higher temperature evaporates more water driving more H2O and CO2 into the atmosphere. The process "runs away."

The CO2 has nowhere to go since neither C nor O can escape; but solar UV breaks up the H2O and the H can escape, leaving behind the O.

That rusts surface rocks. Since all the 02 on Venus rusted away, it would probably rust away on all small rocky planets without life.

Right. That was my point... I think we agree with each other.

The presence of large amounts of atmospheric O2 may well be an indication that a planet has largescale biological activity going on.

Why are we so concerned about finding oxygen.

Is there any reason why oxygen is needed for life? Are we basing this on our own observations of life or is there some reason that without oxygen, life cannot exist?

It is not that oxygen is needed for life.

It is that life *can* produce large amounts of free oxygen in the atmosphere (and did on earth), and we may be able to detect oxygen in the atmosphere more easily than other signs of life.

Thanks for the answer.

I have learned so much from SMP that even though I sometimes feel like I am a ******, I think of myself as SMP's ******.