

NASA's Curiosity Rover Finds Biologically Useful Nitrogen on Mars - denzil_correa
http://www.nasa.gov/content/goddard/mars-nitrogen/index.html?linkId=13093784#.VRGSKfnF-Ag

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liquidise
Perhaps someone with a stronger chemistry or biological background can clear
this up for me: do we assume extraterrestrial life will rely on the same
chemistry as earthen life simply by virtue of limited observation? Is there
some evidence that life, given a different starting planet, would like still
form from chemicals readily found on earth?

Or, i suppose, does it just make for clickable headlines?

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netcraft
I believe it is theorized that life could use silicon instead of carbon, but I
think for the most part we just look for what we know works. They are just
saying that earth life could have lived on Mars at some point in the past,
that the conditions would have been favorable for it. Other kinds of life
could exist in other environments, but we don't have any litmus for those
observations yet.

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Gravityloss
The problem is that silicon dioxide is a solid unlike carbon dioxide.
"Breathing" it out is a lot harder.

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torrente
Why would you assume these organisms would breathe?

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jerf
Because all organisms need to expel entropy to survive, and expelling solid
entropy is a fairly non-trivial engineering problem vs. the life that we do
know expelling it via liquids and gasses. Heck, it's not even all that clear
how to do that just as a machine... nothing is coming to mind that does that
today. (Examples welcomed. Also note that for today's discussion execrement is
solids suspended in a liquid, not a "solid". Silicon is a _solid_ , you know,
rock-solid, literally.)

The idea that we have "no idea" what life could look like out there in the
universe is grossly oversold. We actually can put a lot of bounds on them,
using rigorous mathematics, and discuss them despite not necessarily knowing
all the chemical details.

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ars
> Heck, it's not even all that clear how to do that just as a machine...
> nothing is coming to mind that does that today.

That's basically ash, think of a coal burning plant and how they deal with
waste.

Or iron smelting, how they leave the waste slag behind.

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jerf
Bingo. Thanks. I knew there had to be something.

It's difficult to see how this could be made to work for a life form, because
this is a very macroscopic process. On a microscopic level, well, we're all
just ugly bags of mostly-water so we do it by suspending things in our mostly-
water. As I understand it there are few to no good candidates for a silicon-
friendly liquid base when you work through it.

(Interestingly, I have seen some suggestions that there could be other liquids
that carbon-based life could be based on, such as ammonia. That said, it may
not be coincidence that water is still almost certainly the best (accounting
for the possibility that it's just the observer effect), and that's what all
life forms reading this for the forseeably future are based on.)

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ars
It might be like how the body builds bones. The alien could do the same with a
glass bone, and excrete it every so often.

If they are like humans they would emit a 1 to 2 KG bone every day.

Glass is pretty inert though, I wonder how it would decay/decompose.

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serf
>> Glass is pretty inert though, I wonder how it would decay/decompose.

into beautiful alien beaches, around tidal oceans of ammonia.

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ars
That would be like you enjoying a lake made of urine.

To this alien the glass would be gross and icky.

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iwwr
Please note that nitrogen in the air is also biologically useful, given
nitrogen-fixing bacteria. Legumes and other plants live in symbiosis with
nitrogen-fixers.

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hashmymustache
not to mention Blight

