scott <sco### [at] scottcom> wrote:
> How come?  Didn't life as we know it develop because there was plenty of 
> water around?  On planets or moons much further away where another 
> liquid is in plentiful supply (eg methane) couldn't some kind of life 
> develop that uses that instead?  What's the general definition of life 
> (without referencing the specific life we have on Earth)?

  Do other liquids have the same chemical properties advantageous to the
forming of life?

  Also, other liquids often require such cold temperatures that the planet
may be uninhabitable for that reason: It doesn't receive enough energy from
the Sun to form or sustain life.

  Also, if the liquid gets a higher density when it freezes, it can become
a problem with respect to forming life.

-- 
                                                          - Warp

Post a reply to this message

>>> (Also, most liquids other than water get denser when they
>>> solidify, which is a big problem.)
>
>> Care to explain why?
>
>    If water had a higher density when it freezes (as happens with the vast
> majority of other chemical compounds), life on Earth wouldn't exist because
> all bodies of water would freeze from the bottom up, killing all living
> organisms.

Is it a requirement of life to have frozen water around?  Couldn't life 
start on a planet where there were areas that never froze (or at least 
didn't freeze for long enough for life develop sufficiently)?

Post a reply to this message

Invisible <voi### [at] devnull> wrote:
> Evolution asserts that species are not fixed; they /change/. And so the 
> species we see today were not always there. And, in particular, not so 
> much evolution itself, but molecular evidence says that all life on 
> Earth has a single common ancestor.

  Actually the definition of "species" is a hard one.

  By definition two animals are of different species if they cannot produce
fertile offspring. However, this definition is lacking.

  It's lacking because the definition implies transitivity: If A can reproduce
with B (thus A and B are of the same species), and B can reproduce with C
(thus B and C are of the same species), by definition A and C should be of
the same species (and hence able to reproduce). However, there are eg.
so-called ring species (look it up) where this doesn't happen: It may be
that A and C cannot reproduce, making them by definition members of
different species, even though B can reproduce with either A or C. This
makes a clear definition of B's species rather difficult.

  (And with ring species we are not necessarily talking here about some
weird obscure unicellular organisms living in the depths of the ocean
which defy all classification. We are talking about regular everyday
animals, such as certain species of seagull.)

  A ring species is actually an excellent demonstration of how speciation
can happen gradually, unlike the straw man that some creationists present
of "a species suddenly transforming into another": Yes, it *is* possible
for a subgroup of a species to *slowly* transform into a different species
over time, and during this period the ability of procreation between the
two groups gradually becomes less and less possible (the probability of
a successful fertilization becomes smaller and smaller because of the
constantly increasing differences in genes). If this subgroup further
spawns an even more isolated sub-subgroup, we may end up precisely in the
situation where a member of group A can procreate with a member of group
B, and a member of B with a member of C, but a member of A cannot procreate
with a member of C.

  The difficulty of classifying B in the example also demonstrates the
completely fuzzy line between when a species becomes another species.
If you trace the ancestry of a modern species back to an ancestral species
which spawned one or more other modern species, it's hard to define when
exactly the modern species became to exist exactly. By definition every
offspring is of the same species has its parents, but if you continue
this back long enough, you end up with animals that are so different from
the modern equivalents that they cannot be considered of the same species
anymore (if that ancient species was brought back to life today, it would
be unable to reproduce with its modern descendant). However, drawing the
dividing line where the ancient species became the modern one is impossible.
It's a fuzzy line.

-- 
                                                          - Warp

Post a reply to this message

Darren New <dne### [at] sanrrcom> wrote:
> Warp wrote:
> >   (I read somewhere that recently Barack Obama decided to announce the
> > National Day of Prayer, or something like that, 

> The "national day of prayer" has been around since we were fighting the 
> godless communists (I kid you not) in the 1950's, passed by Congress at the 
> time. That's the same time we got "under god" added to "one nation under 
> god" in the pledge of allegiance.  Given that Obama keeps referring to 
> atheists in all his speeches (which ticks off the religious folks) I would 
> guess (without a cite) this is at least as much a lie as half the other 
> things said about him.

  Well, perhaps this will do for a citation:

http://www.snopes.com/politics/obama/prayerday.asp

"Observances of the National Day of Prayer took place throughout the
U.S. in 2009 and again in 2010. The status of the National Day of
Prayer is currently somewhat uncertain, though, as on 15 April 2010 a
federal judge ruled in favor of a challenge brought by the Freedom
from Religion Foundation and held that the National Day of Prayer is
unconstitutional. The Obama administration was actually the defendant
in that suit, arguing in favor of retaining the National Day of
Prayer."

-- 
                                                          - Warp

Post a reply to this message

scott <sco### [at] scottcom> wrote:
> Is it a requirement of life to have frozen water around?  Couldn't life 
> start on a planet where there were areas that never froze (or at least 
> didn't freeze for long enough for life develop sufficiently)?

  I don't know. There are tons and tons of things that allowed life to
form of Earth, and changing even one of them would have made it a lot
more difficult, if not impossible. (Christians will say that the Earth
is like that because God created it like that. Scientists will simply
point out the anthropic principle: Earth was not created for us. We are
on earth because of all the countless random planets on the Universe Earth
happened to be optimal for the formation of life, so it did.)

  It might be that if the weather system on Earth (over periods of millions
of years) was such that water never froze at large portions of it, it might
be hostile for life for other reasons. Perhaps a changing climate is somehow
necessary for life. As said, I don't know.

-- 
                                                          - Warp

Post a reply to this message

>>>     Of course for the water to be any good, it has to be in liquid form.
>
>> You're aware that (on Earth) there are organisms that live in solid ice,
>> right?
>
>    They did not originate in ice. The simply adapted to it afterwards.

That's true. It's also true that planets that are far from the Sun right 
now might have been nearer at some point. Or the Sun's output may have 
changed.

But ultimately, yes, it seems more plausible that life would originate 
and thrive in a liquid or possibly vapour environment, rather than a 
solid one. (I have no idea whether it's feasible in plasma.)

>> What makes you think that chemicals which are "rare" on Earth would
>> necessarily be rare elsewhere?
>
>    There would have to be a significantly different process that formed
> those rare elements than here on Earth. What would that process be?

A cursory glance at the chemical composition of the surface or 
atmosphere of various planets around us indicates wildly differing 
chemistry. I don't know enough about planet formation to speculate as to 
why. (Presumably different elements get transported to different places 
or something...)

>>> (Also, most liquids other than water get denser when they
>>> solidify, which is a big problem.)
>
>> Care to explain why?
>
>    If water had a higher density when it freezes (as happens with the vast
> majority of other chemical compounds), life on Earth wouldn't exist because
> all bodies of water would freeze from the bottom up, killing all living
> organisms.

OK. But presumably that's only "a big problem" if the chemical we're 
talking about has a solid phase that can potentially exist on the planet 

your hypothetical planet never gets that cold, the fact that solid 
ammonia is more dense than liquid ammonia shouldn't be a problem.

Post a reply to this message

> On planets or moons much further away where another liquid
> is in plentiful supply (eg methane) couldn't some kind of life develop
> that uses that instead?

I would say it's plausible.

Water's chemistry is somewhat unusual in a number of ways (particularly 
the fact that it can dissolve such a wide range of solutes), but it 
seems plausible to me that you could use some other solvent.

Post a reply to this message

>    It might be that if the weather system on Earth (over periods of millions
> of years) was such that water never froze at large portions of it, it might
> be hostile for life for other reasons. Perhaps a changing climate is somehow
> necessary for life. As said, I don't know.

I don't know either, which is why I wouldn't dismiss the possibility 
that life could start in other liquids.

Post a reply to this message

On 11/01/2011 02:03 PM, Warp wrote:

>    Actually the definition of "species" is a hard one.

Yes, actually.

I suppose back when everybody thought that all life was fixed and 
unvarying forever, it seemed less problematic. But now that we know that 
one species gradually changes into another... it's a bit like trying to 
classify whether a specific colour is "red" or "orange". The distinction 
is almost arbitrary.

>    By definition two animals are of different species if they cannot produce
> fertile offspring. However, this definition is lacking.
>
>    It's lacking because the definition implies transitivity:

There's a much bigger problem: Some species reproduce asexually. (!)

> However, there are eg. so-called ring species (look it up)

Another of the interesting items from The Ancestor's Tale which my 
initial post skipped over. A continuum of organisms, distinct at the 
ends, but continuous and unbroken across the middle.

>    A ring species is actually an excellent demonstration of how speciation
> can happen gradually, unlike the straw man that some creationists present
> of "a species suddenly transforming into another".

It also neatly demonstrates that geographic separation is not a 
necessary condition for speciation.

>    The difficulty of classifying B in the example also demonstrates the
> completely fuzzy line between when a species becomes another species.
> If you trace the ancestry of a modern species back to an ancestral species
> which spawned one or more other modern species, it's hard to define when
> exactly the modern species became to exist exactly.

Ring species show fuzziness in the spatial domain, ancestor trees show 
it in the temporal domain. Either way, the problem remains the same: how 
to map discrete names to continuous phenomena?

Post a reply to this message

Warp wrote:
>   I don't think it would be physically possible for any kind of life to
> form that far from the Sun.

There's the Vernor Vinge story "A deepness in the sky", wherein the 
protagonists evolved around a sun that was hot only a few decades out of 
each several centuries and managed to hibernate through the cold times. I 
imagine something like that with a comet could work out. Hard to see how it 
would *evolve*, mind, unless the body started out in a close orbit that got 
more and more eccentric over time somehow.

>   Chemicals need to react with each other, which means that there must be
> some kind of solution where they can freely float or otherwise move.

Weightlessness?

> (Also, most liquids other than water get denser when they
> solidify, which is a big problem.)

I'm not sure that's as much of a problem as you think it is for anything 
other than fish.  Why do you think the fact that it floats is important?

Also, it floats in part because it's a polar molecule (i.e., electrically 
asymmetrical), which may very well be more important than the result of 
floating.

-- 
Darren New, San Diego CA, USA (PST)
   Serving Suggestion:
     "Don't serve this any more. It's awful."

Post a reply to this message