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Comment by Aachen | Hacker News Reader

So... I understand like seven words in your comment so forgive me if I'm mistaken, but I don't think this answered the question in the comment you're responding to? They asked whether it could have been picked up in the atmosphere, not whether it's of biological origin in the first place (that would be the parent post).

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It hints at the answer. Most amino acids on Earth occur in the L configuration because they are mostly synthesized through biologic activity. This is not to say there are no D amino acids in living organisms -- they're just uncommon. And abiotic processes tend to produce racemic mixtures, but these products are in the minority. Basically, amino acids found on Earth, even in the atmosphere, strongly favor the L configuration. Analyzing the fraction of L and D amino acids within the meteorite would yield clues as to their origin.

Living organisms use nano machines called proteins which physically make molecules like glucose out of other molecules.

Some molecules can form in 2 ways that are mirror images of each other. However, making or using both versions would require having twice as many proteins so we only produce one version of anything.

To visualize this consider DNA is a spiral, you could reverse everything so the spiral rotated in the other direction. But then everything interacting with DNA would also need to be built for that orientation and so forth. https://en.wikipedia.org/wiki/Mirror_life

Here is a video talking about molecular chirality and how nature really only produces one version of molecules https://www.youtube.com/watch?v=SKhcan8pk2w. If it picked up the molecules in the atmosphere those atmospheric molecules should have been made by life on earth and those have a handedness bias depending on the molecule, some are produced right handed only or left handed only because they are made one atom at a time and need to be one handed for life to use them. Abiotic synthesis produces a 50/50 bias of left and right handed molecules because they are made all at once.

The presumption is that it would necessarily be of biological origin if it were picked up in atmosphere.

I think the parent was asking if there's a separate family of abiotic amino acids in the upper atmosphere? Like from UV photochemistry stuff.

(I don't know the answer either)

That's an interesting question and I don't know the answer! But I'd expect any amino acids produced this way to diffuse and mix with the biologic amino acids from the surface. They'd be diluted by the overwhelming amount of biological "stuff." Stereoisomers should behave the same under the influence of gravity.

- "Stereoisomers should behave the same under the influence of gravity."

Only one way to find out!

https://sci-hub.se/https://doi.org/10.1103/PhysRevLett.121.2... ("Test of the Equivalence Principle with Chiral Masses Using a Rotating Torsion Pendulum")

Biological processes tend to clone the molecules perfectly right down to specific left or right handed orientations. So the molecules formed from a biological process will all be identical.

A process that just happens to form the molecules (eg. put a bunch of elements in a soup and heat and you can also get some proteins forming) form an even mixture of configurations.

It answers the question.

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