Atmospheres

[Fyron]

There is a famous equation called the Drake Equation which mathematically sets the probability of life in the universe.

Yes, and it attempts to determine the relative number of life-supporting planets in the universe. So what? It has nothing to do with atmospheres that do or do not support life, or with gases that can be used for energy purposes in organisms.

There is a vast range of types of life on earth - plants, animals, people, viruses, bacteria, etc. Even on earth, we have microbes that exist in the polar ice caps and others in the sulfur vents of volcanoes, neither of which use oxygen and both conditions are deadly to humans.

There are molecules that can replace O2, but some organisms on Earth can use H2, H2S, S, HNO3, H2SO4, and CO2 in lieu of O2. But as I've said before, they just don't make enough energy to be useful for anything more than a bacteria, and in that case, it has to have little or no competition!

This is why I have been careful to always say "complex organisms" instead of just "organisms".

Yes, humans couldn't have evolved without O2, but we would have evolved differently in another atmosphere.

Assuming that is actually possible in the first place.

So there are lots of examples here on earth.

Yes, examples of simplistic organisms that do not need very much energy to survive. All complex earth-based organisms use O2 to get energy. Even plants use O2 to break down the glucose they make to get energy. They just make a lot more glucose than they use, which is why they put out a lot more O2 than they do CO2.

How exactly would Ammonia, Methane or Sulfur Dioxide be used to get energy for complex organisms (not monerans, not protista, not any other forms of microscopic life)?

[ February 20, 2003, 05:57: Message edited by: Imperator Fyron ]

[Captain Kwok]

Originally posted by Imperator Fyron:
How exactly would Ammonia, Methane or Sulfur Dioxide be used to get energy for complex organisms (not monerans, not protista, not any other forms of microscopic life)?

They would generally replace O2 in some sort of Version of the electron transport chain, which drives the production of ATP, the major energy carrier in the cell. Instead of O2 being the final electron acceptor to make H2O, one of the other compounds like SO4- (to H2SO4) would be. I suppose if there was lots and lots of the substance available in the alien cell, it might be able to produce enough energy. The problem is that the reduction potential is less than most of the energy carriers in the cell, so it needs to use more energy to get things started.

Some of the substances mentioned before work better as electron donors than acceptors, like ammonium, NH4+. For example, we use H2O as our electron donor for ATP synth, but on a planet with abundant NH4+, it might be possible for more complex organisms to use it the same way that nitrifying bateria do on Earth, but that still requires moderate levels of O2. However, it's just not energetic enough to be effective. But... H2 as an electron donor is fairly energy rich and might be able to form some sort of pathway, but I'm not so sure about the plausability of that.

[ February 20, 2003, 05:43: Message edited by: Captain Kwok ]

[Rexxx]

Originally posted by Slick:
There is a famous equation called the Drake Equation which mathematically sets the probability of life in the universe. You can look it up for further reading. It basically comes out to a mathematical certainty because of the sheer number of stars that we can see that there is life out there somewhere. The real question is what is it like.

Several months ago I read "Rare Earth" by Peter Ward and Donald Brownlee (a paleontologist and an astronomer IIRC).
The rare earth theory is that though bacterial life may be common in the universe, intelligent life - in the form of terrestrial animals and plants - is unique.
Their modifications to the Drake Equation are quite interesting. I do not know enough about the the topics they raised tp prove them right or wrong. Anyway, it's a book well written and full of ideas new to me. I never would have thought of plate tectonics as crucial for evolution on Earth.

[Arkcon]

Originally posted by Rexxx:
I never would have thought of plate tectonics as crucial for evolution on Earth.

I only just started hearing about that one myself. Often people claim some robust life would live on Mars or Venus. But without plate tectonics, atmospheric gases on Mars just get locked up.

Venus, the Last I heard, has a different problem. The most recent radar mapping of it's surface seems to imply that the entire surface is no more than 100 million years old -- all of it, the same age. I wouldn't want to be there when the entire planets surface decides to "recycle"

For SE4, as it's been said already, I would like it if there was more variety to the planets -- some that were just about useless for colonization.

But the AI needs some work to be able to make good decisions about these. Recently I went MEE, so I started using the planet conditions bomb. After all, I have all the planets I need. This seriously crippled the AI -- it saw the empty planets and colonized them -- and couldn't really thrive with 25 deadly planets.

[ February 20, 2003, 13:47: Message edited by: Arkcon ]

[solops]

Plate tectonics - yes, Everyone ought to have to take Physical Geology in college. Plate tectonics and the sun drive and define our environment, which in turn defines the life-forms on the planet. I am still not convinced that you could not have life on a "non-tectonic" planet, but its development would be far different and more sedate.

And, I still want a "build queue finished message" and a main screen components readout by right-clicking on an enemy ship :-)

[ February 20, 2003, 15:09: Message edited by: solops ]

[Slick]

I wasn't real clear about the applicability of the Drake Equation to atmospheres. Actually the complete Drake Equation is the probability that intelligent live elsewhere will contact us - not about proving that life is out there. There are a number of factors in the equation, but the applicable one is: fl (f "sub l"). fl is "the fraction of suitable planets on which life actually appears".

If you delve into the development of this factor, it considers a number of environmental effects, including atmosphere, distance from the star, water content, etc.

If any of you college people out there are looking for a good science elective to fill, consider a 2nd year astronomy class. Don't go for the one that shows pretty slide shows every day. Look for the one with a textbook that has a bunch of physics equations in it. I did that when I was in college and it turned me on to astronomy as a favorite reading subject. As a side note, if your college/university is near any large observatories (like we have in Hawaii), you will find that many of the leading astrophysicists will be around due to the telescopes and teach courses in their spare time, so you can learn from some real high-powered people.

Slick.

[Fyron]

Ok. The Drake Equation now has even less to do with this discussion.

Drake was not infallible, you know.