Alien goo fell from the sky!!!

[wacki]

With so many threads about life on other planets, god, etc. I thought I should repost some proof that life does exist outside of this planet.


Murchison Meteorite

Although astronomical processes have been hypothesized, no nonbiological process is known to produce this asymmetry. Instead, the case for life forms or life's chemistry in meteorites has always been open to the suggestion that meteorites are easily contaminated with biological products after reaching Earth (6). However, even before the new work by Cronin and Pizarello was reported, analyses of isotope ratios showed that the excess of left-handed amino acids in the meteorite was not the result of earthly contamination (7).

The above link is very significant.

Also: Life on Mars

[gumpzilla]

[ QUOTE ]
With so many threads about life on other planets, god, etc. I thought I should repost some proof that life does exist outside of this planet.

[/ QUOTE ]

I'm not sold. Amino acids, while certainly suggestive of life, don't really seem like strong enough evidence for me to be convinced. Perhaps you'd care to elaborate on your definition of life?

[wacki]

Amino acids isn't the proof. It's the chirality of the amino acids. Nonracemic mixtures simply do not happen randomly. Reread the link carefully.

THat being said, very few people here have the educational background to understand this. Still, with a dictionary and google, it's not that hard to teach yourself.

[gumpzilla]

[ QUOTE ]
Amino acids isn't the proof. It's the chirality of the amino acids. Nonracemic mixtures simply do not happen randomly. Reread the link carefully.

[/ QUOTE ]

Fair enough, I did pretty much blast through it.

That said, I think one can certainly conceive of scenarios that might select for amino acids of a certain chirality that don't involve life. Suppose you have a collection of amino acids, both left and right handed. Now expose them to a circularly polarized light source such that one handedness absorbs heavily and the other doesn't. Perhaps this will lead to the right handed amino acids breaking up disproportionately, leaving you with predominantly left handed amino acids. My roommate has a pet theory - perhaps this is something that biologists actually already have an opinion about - that this is why biological proteins have a particular handedness. Our atmosphere does a good job of screening one kind of circular polarization, as I recall.

[wacki]

True, but there are some problems with that theory as described here:

http://www.ast.cam.ac.uk/AAO/local/w...chirality.html

Granted it is still possible.

[gumpzilla]

Is the problem you're mentioning the lack of appropriately circularly polarized light from neutron star sources? I don't think that's a big deal. Circularly polarized light isn't all that tough a thing to come by. All you need is different indices of refraction for the two different linear polarizations and you're in business. Plenty of natural crystals have this property. My knowledge of astronomy/cosmology is disgracefully poor, so I'm not sure how realistic this scenario is, but birefringence is pretty common and it wouldn't surprise me to find that one could cook up a reasonable scenario allowing it before life. There was also the suggestion that light observed from some nebulae appeared to be strongly circularly polarized.

And I was also not referring to this theory directly, which seems to be keen on the notion that the asymmetry came in before life. I'll have to dig out my copy of Jackson and look at the atmosphere/circular polarization bit, but if slightly increased absorption leads to an unfortunately high mutation rate, you could see wrong-handed DNA die out because it isn't a faithful enough replicator, possibly. (Yes, I am talking out my ass.)

[Subfallen]

[ QUOTE ]
My knowledge of astronomy/cosmology is disgracefully poor...

[/ QUOTE ]

I'd hate to have you assess my knowledge of anything then. How are you so well-educated? (I'm not being sarcastic, genuinely interested.)

[gumpzilla]

[ QUOTE ]

I'd hate to have you assess my knowledge of anything then. How are you so well-educated? (I'm not being sarcastic, genuinely interested.)

[/ QUOTE ]

I'm a Ph.D student in physics, so you've caught me in my field. When I say my knowledge of astronomy is really bad, I mean it's really bad for a physicist. Lots of stuff I'm ignorant about up there that I really shouldn't be. Cosmology is one of the most popularized branches of physics, and it's hyped up a lot, but a lot of people I know (myself included) have a certain amount of disdain for it. Mostly this is because I think the dark matter problem sounds silly, and I don't have a good idea how much of what is known or speculated about astronomical/cosmological problems is grounded in really solid science. This is not the greatest attitude to have, so I really should learn something about it at some point.

The business about circularly polarized light is much more down to earth (ha, ha) and is something that I have at least had some exposure to, which is why I can spout off about that.