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Comment by photochemsyn | Hacker News Reader

They found amino acids as well, pretty strong evidence for a role in the delivery of organic compounds to the early Earth (though abiotic synthesis of such compounds at hydrothermal vents is also plausible):

> "The macromolecular organic fraction of a driveway fragment was analyzed by gas chromatography–mass spectrometry (GC-MS) and found to contain structural units similar to those in other CM chondrites, including substituted benzenes and naphthalenes, various thiophenes, and polycyclic aromatic hydrocarbons. The most abundant amino acids detected in the Winchcombe meteorite were α-aminoisobutyric acid (467 ± 17 ng g−1) and isovaline (391 ± 17 ng g−1; table S23). An extraterrestrial, abiotic origin for these compounds is supported by the racemic enantiomeric ratios detected in several protein and nonprotein amino acids (e.g., D/Lalanine = 1.13 ± 0.16; D/Lisovaline = 1.06 ± 0.15)."

https://www.science.org/doi/10.1126/sciadv.abq3925

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Is it possible that the meteorite picked up the amino acids from Earth's atmosphere or during the impact?

If you collect a sample of biologically synthesized amino acids, the central carbon atom will have only one stereoisomeric form, i.e. like a left hand vs. a right hand, due to how these amino acids are synthesized by biochemical systems, i.e. enzymes which only generate L-amino acids from precursors (indeed protein structure depends on this asymmetry). There are a handful of exceptions but since the amino acids collected from the meteorite are a racemic mixture (equal amounts of both left and right handed molecules), this points to abiotic synthesis.

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).

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.

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

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.

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.

It answers the question.

I did not understand a single thing you just said. I'm in awe.

As a follow-on question to this: what is the process by which meteorites are analyzed? It seems like the contamination problem could be solved by drilling.

If life arrived on Earth from space, that's kind of a bummer because now the mystery of life's origin (our pocket of life at least) is far out there, beyond our reach.

Sort of. Earth's surface is constantly being recycled. Rocks from when life began on earth have all but completely disappeared. Meanwhile, rocks from or older than that are still completely preserved whizzing around the solar system.

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