Beth, perhaps you can shed some light on this. Seems an appropo time to bring
it up.
on 02.6.26 1:34 PM, Beth.Fulton@csiro.au at Beth.Fulton@csiro.au scribbleth:
> After the last major comet collision the major herbivore niche was
Terran animals use stones for support, presumably because Ca-based
structures are relatively easy to form given water-based transport, and
Ca is plentiful in the environment. While there are some snails (IIRC; I think
you told me that, actually) that use Ti for an oxygen-transport
mechanism, I don't know of any structural uses of metal or metallic compounds.
Why not? Just because the useful metals are not as chemical active as Ca? (and
the ones that are active aren't common) Fe seems to have plenty of useful
reactivity, considering we use it to transport O2 ourselves.
Are there are chemistry- or physics-related reasons why metal structures
aren't found in nature? (real answers, theories, sheer guesses and tall
stories all welcome)
G'day,
> Beth, perhaps you can shed some light on this. Seems an
My biochem is shaky I'm much more an ecological theorist, but I'll have a
crack (then maybe John Lambshead or someone can correct me).
> I don't know of any structural uses of metal or metallic
Based on my limited biochem knowledge (I dodged uni chem by doing math) its
due to the chemical properties of metals. Metals have to be in specific forms
to be biologically available in the first place (e.g. methylmercury vs pure
mercury) and then its a matter of how much it takes to gum up the biological
works by overloading receptor sites etc. For instance some metals
can overwhelm/change receptors that are there for another purpose (in
much the same way as carbon monoxide will block haemoglobin from carrying
oxygen). Biological structures can often cope with some metals, but too much
is a bad thing. That's why we need a certain amount of iron to keep the body
up to its full potential, but too much and you've got severe blood chemistry
imbalance and the potential for damage to major organs. Its particularly a
problem in multicellular organisms so bacteria can more readily handle metals
or concentrations other organisms would find toxic. So for Terran animals I'd
say for those metals that are not currently utilised already (so calcium is,
but to my knowledge nothing uses gold (say) as a major intentional skeletal
component) that in trying to get enough material together to make a support
structure they'd end up poisoning themselves or if they had to purify it so it
couldn't flood back into their system then many metals may end up being to
brittle compared to the strength of things like chitin.
Sorry I can't be more precise
Sounds like metals won't work for Terran organisms, but there's no particular
reason why they couldn't work for organisms using a different chemistry. As
far as physics and chemistry are concerned, there don't seem to be any special
obstacles, right?
Which means that your titanium-shelled bugs and titanium-munching wasps
are
at least as possible as anti-grav tanks. Probably more so, come to think
of
it...
on 02.6.26 4:45 PM, Beth.Fulton@csiro.au at Beth.Fulton@csiro.au scribbleth:
> So for Terran
As far as brittleness, organisms are pretty good at creating composites to
improve various engineering properties. I don't see this as a problem at all;
it could easily have lattices of something else in it, if it's built up
through accretion in atomic (or molecular) units.
> if they had to purify it so it couldn't flood back into their system
G'day,
> Sounds like metals won't work for Terran organisms, but there's no
Yep... its actually an interesting thought experiment as to whether biologies
based on different chemistries can exist... are we refined to the chemistries
we see today because their precursors were the only ones that turned up or
because they're the only ones that can turn up;)
> As far as physics and chemistry are
As far as I know, but the chemists and physicists may have something to say
about that. Having said that certain chemicals are more suited for certain
tasks (e.g. Carbon due to its flexibility, electron shell config etc).
> Which means that your titanium-shelled bugs and
And much less against my grain than biological things functioning in a
vacuum... not that I'm about to throw the SV baby out with the biological bath
water;)
> As far as brittleness, organisms are pretty good at creating
Yep, though I'm not sure where the matrix size would fall on that. Though my
"battle suits" sort of use the same idea in that they're made form a "living
composite alga". Basically they're a chemical structure derived from algal
colonies that is kept "alive" inside thin self repairing suits (that just
happen to look like everyday battledress from a distance). They're flexible
enough to allow everyday movement without restrictions, but when hit hard or
with high intensity (e.g. shrapnel, bullet, sharp edge or point) they act like
a rigid body (think of the difference between when you enter water quickly or
slowly). This gives the wearer roughly the same protection as D6 (or for
really good suits D8) armour with the added bonus that the suits have a
cryptomatch ability (like octopus cam). Though diseases can dull the colour
change ability and too many quick transitions can lead to colour lag.
Cheers
And if you forget to feed and water them, they sometimes (accidentally, of
course!) eat the wearers.
They were mentioned in Gear's "Forgotten Borders" trilogy, now that you
mention it.
on 02.6.26 5:13 PM, Beth.Fulton@csiro.au at Beth.Fulton@csiro.au scribbleth:
> Yep, though I'm not sure where the matrix size would fall on that.
Though my
> "battle suits" sort of use the same idea in that they're made form a
G'day,
> They were mentioned in Gear's "Forgotten Borders" trilogy,
Can I have the details please? (Another case of "I haven't read enough scifi
to know when I'm dreaming up stuff greater people have already described")
Thanks... though mine don't eat the wearers if neglected they just look sad
;P
From: Beth.Fulton@csiro.au
> Yep... its actually an interesting thought experiment as to whether
I believe there's something about this in Steve Gillett's book on
planetbuilding.
> And much less against my grain than biological things functioning in a
I don't mind biologicals operating in a vaccum although I imagine the outside
layers would get quite brittle. What bothers me is a biological main drive....
> thin self repairing suits <snip>. They're flexible
Water behaves this way simply because you have to shove the mass aside, but if
you have thin suits which don't restrict movement, you can't be talking about
that much mass. I assume you meant this as an illustration of the effect but
not the cause?
G'day,
> Water behaves this way simply because you have to shove the
Yes.
Cheers
on 02.6.26 5:25 PM, Beth.Fulton@csiro.au at Beth.Fulton@csiro.au scribbleth:
> They were mentioned in Gear's "Forgotten Borders" trilogy,
Basically, it was as you described. When impacted the material became very
hard and could spall. It did not resoften. Troops coming out of combat often
had armor hardened to the point where mobility was affected. The organic armor
lived off occupant sweat, with (possibly, it wasn't explained fully) excrement
etc. They did not eat their wearers. It was more of an organic material than
an organism.
The books are, unfortunately, mediocre. Gear sets up a very artificial
universe with all sorts of artificially-imposed restrictions, to make
his points. A lot of the restrictions get in the way of
suspension-of-disbelief.
BTW.
Here are a few comments from my mother, who was a biochemist/gengineer
for 30 years. May serve to stimulate someone's imagination:
You have to differentiate between circulating ionic forms of metals and those
laid down as comparatively insoluble salts. Thus, an oversupply of ferric or
ferrous
ion in the blood is deposited as an iron-protein complex, called
hemochromatin, in the liver, where it eventually reaches a mass which
interferes with liver function. Too much calcium ion in the blood can
interfere with muscle contractility, particularly in the cardiac muscle, but
it can be immobilized as the calcium compounds in bone. Lead is poisonous but
useless, and can to some extent also be sequestered in bone. Lighter metal
ions such as sodium and potassium are powerful and the heart is exquisitely
sensitive to their concentrations. The ancient Chinese used to kill people by
making them eat a lot of salt, and the occasional serial murder who is a nurse
often injects potassium chloride into the IV tubing.
I think this might demonstrate what Beth is talking about perfectly:
Needed:
A container. Some water Baking powder (not soda).
Fill the container with about 1/4"-1/2" of water.
Slowly sift in lots of baking powder. You want to make sure what is in the
container is soaked before adding more. Add enough to that the
baking powder looks wet but doesn't flow or have free-standing water in
the container.
Now you have it. Take your finger or a pencil and try to jab it quickly into
the muck you just made. It won't give, if you hit it hard enough it may even
break apart in a crumbly way. Now slowly press your finger into it... it gives
and flows slowly away.
You really ought to let some kids play with this stuff a bit, so you can
justify having used up this much baking powder...
> On Wed, 2002-06-26 at 19:41, Beth.Fulton@csiro.au wrote:
I thought it was corn starch. It forms a non-newtonian fluid in which
it gets harder the more pressure that is applied. IIRC it has to do with the
water squeezing out as pressure is applied.
--Binhan
> -----Original Message-----