Freethought & Rationalism Archive

Coragyps · 08-25-2002, 09:03 AM

I won't go so far as to say it can't happen, but carbon likes to make big molecules by bonding to other carbons, and silicon doesn't do that very well - it prefers to incorporate oxygen in its long chains. This sort of limits the complexity that silicon chemistry has relative to carbon, and may be a real deterrent to building life.
Though I sure did like some SF story from Analog about 1960, with critters that breathed chlorine....

KeithHarwood · 08-25-2002, 04:58 PM

Quote:

Originally posted by Sunfair:


Just out of curiosity, is it specifically carbon-based life? I know we haven't encountered any other kind- but I was wondering if it's generally believed that other kinds of life would also be dependant on water? Like, silicon-based (no Hollywood jokes please), or nitrogen-breathers or whatever- not that I would know, but I like to speculate.

I hope that made sense, I'm kinda tired.

At low temperatures and high pressures (e.g. gas giants) ammonia is a plausible substitute for water for carbon-based life-forms. However, I don't think anyone has done any serious investigation of the chemistry involved.

KeithHarwood · 08-26-2002, 03:45 PM

Quote:

Originally posted by DougI:
Argued with a stupid YEC (yup, that's redundant) and he used the easily refuted argument about life only existing in particular circumstances. Although I had to explain to him the Earth travels around the sun in an ellipse (not a circle like he claimed) I wasn't sure how much of a degree difference outside a perfect circle it traveled. He argued that anything outside a five degree difference would be impossible, I just wasn't sure about the actual difference.

I think he is confusing eccentricity (the amount of out-of-round of the orbit) with the inclination (the angle between the plane of the planet's orbit and the plane of the earth's orbit). The first is a pure number ranging from about 0.0068 (Venus) to 0.25 (Pluto). The second is measured in degrees ranging from 0.77 (Uranus) to 17 (Pluto).

There is a creationist argument along the lines of `if the earth's orbit wasn't so nearly circular the climate would be very unpleasant for human beings therefore God Did It'. There is another one that starts off with all the inclinations being small and ends with God Did It, but I can't remember how it goes. I suspect your correspondent has conflated the two and doesn't understand either.

For the record, the earth's eccentricity is about 0.0167 and its inclination is, by definition, almost zero. (Why it isn't exactly zero is left as an exercise for the reader.)

Late_Cretaceous · 08-26-2002, 04:57 PM

Doug, perhaps your creationist friend there only uses 10% of HIS brain.

beausoleil · 08-26-2002, 05:04 PM

Quote:

Originally posted by Sunfair:


Just out of curiosity, is it specifically carbon-based life? I know we haven't encountered any other kind- but I was wondering if it's generally believed that other kinds of life would also be dependant on water? Like, silicon-based (no Hollywood jokes please), or nitrogen-breathers or whatever- not that I would know, but I like to speculate.

I hope that made sense, I'm kinda tired.

I found this little page which seems to sum things up quite well...

<a href="http://www.physics.hku.hk/~tboyce/seti/21strange.html" target="_blank">http://www.physics.hku.hk/~tboyce/seti/21strange.html</a>

Sunfair · 08-26-2002, 10:28 PM

Thanks for your input, everyone. It's an idea worth exploring- even in science fiction mode.

"Dammit, Jim! I'm a doctor, not a bricklayer!"

gravitybow · 08-27-2002, 07:09 AM

Here's an explanation for eccentricity at <a href="http://www.analemma.com/Pages/EllipticalOrbit/EllipticalOrbitMath/EllipOrbitMath.html" target="_blank">http://www.analemma.com/Pages/EllipticalOrbit/EllipticalOrbitMath/EllipOrbitMath.html</a>:

Quote:

An ellipse is a unique figure in astronomy as it is the path of any orbiting body around another. An ellipse is a flattened circle. Two fixed points inside the ellipse, F1 and F2 are called the foci. For the Earth–sun system, F1 is the position of the sun, F2 is an imaginary point in space, while the Earth follows the path of the ellipse.

An ellipse has a special property. The sum of the distances from P1 to the foci is the same as the sum of the distances from P2 to the foci. This is true for any point P on the ellipse. The distance a is the semimajor axis, while the distance b is the semiminor axis.

The eccentricity e of an ellipse is a measure of the asymmetry of the ellipse. It is the ratio of:

distance from center to a focus : semimajor axis

The eccentricity e can be calculated as follows:

The eccentricity of the ellipse in the figure is .661. The eccentricity of the Earth’s orbit around the sun is .017.

And here's a really cool <a href="http://csep10.phys.utk.edu/guidry/java/kepler/kepler.html" target="_blank">Java applet</a> that will let you play with e values to alter the orbit. The e slider is at the bottom of the applet.

Thread Tools	Search this Thread
Show Printable Version	Search this Thread: Advanced Search

08-25-2002, 09:03 AM	#11
Coragyps Veteran Join Date: Aug 2001 Location: Snyder,Texas,USA Posts: 4,411	I won't go so far as to say it can't happen, but carbon likes to make big molecules by bonding to other carbons, and silicon doesn't do that very well - it prefers to incorporate oxygen in its long chains. This sort of limits the complexity that silicon chemistry has relative to carbon, and may be a real deterrent to building life. Though I sure did like some SF story from Analog about 1960, with critters that breathed chlorine....

08-26-2002, 04:57 PM	#14
Late_Cretaceous Veteran Member Join Date: Oct 2001 Location: Alberta Posts: 1,049	Doug, perhaps your creationist friend there only uses 10% of HIS brain.

08-26-2002, 10:28 PM	#16
Sunfair Regular Member Join Date: Jan 2002 Location: USA Posts: 110	Thanks for your input, everyone. It's an idea worth exploring- even in science fiction mode. "Dammit, Jim! I'm a doctor, not a bricklayer!"

Freethought & Rationalism Archive

The archives are read only.