General Question

timothykinney's avatar

How can I detect the difference between biotic and abiotic compounds in a soil?

Asked by timothykinney (2743points) June 9th, 2009

I’m working with some samples in a soil lab and have been asked to propose a hypothesis about the difference between a sample with life in it and a sample with no life in it. I have searched the literature but there is no straight-forward answer to this that I have seen.

I think there are some compounds which are only formed from organic processes and others which are only formed from inorganic processes. So I think this is a starting point. But I don’t know what those processes and compounds are.

Can someone give me a shove in the right direction?

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8 Answers

shilolo's avatar

If you are talking about live, active soil samples, then production of carbon dioxide and loss of oxygen via cellular respiration is a sign of life. In particular, if you boil the sample (which should kill all organisms), and the carbon dioxide production disappears, you have disproven the hypothesis that CO2 is formed by abiotic processes. Now, if you are trying to discriminate between the presence or absence of compounds as a sign of prior biotic existence, there, I don’t have a great answer, but perhaps you can look for the presence of nucleic acids, amino acids or complex sugars. While these can be formed by abiotic processes, it is far more likely to be a sign of prior life.

crisw's avatar

As long as the question is whether anything in the soil was ever alive, I’d look for the presence of humic acids. They indicate that humus is present and humus=organic matter.

Lupin's avatar

DNA and the associated nucleic acids absorb quite nicely in the UV range of 245 to 260 nm a solid peak at 248nm. You can hit it with a relatively cheap UV-C source at 254 nm and measure the absorbency.
Warning!!! -After illuminating with UVC the DNA based life form will no longer be viable so be careful.

La_chica_gomela's avatar


shilolo's avatar

Get a room.

timothykinney's avatar

@Lupin, we also have chromophoric carbon which absorbs in that range in the sample, so that won’t work. Nice idea though.

I think I’ve decided to compare the abundance of lipids, aliphatics, and polyphosphates using NMR and mass spec. Hopefully this won’t be too difficult.

Thanks for the help jellies!

La_chica_gomela's avatar

@shilolo: We will, TOMORROW!!! Yay!!!!

Lupin's avatar

@timothykinney @shilolo In my latest copy of Photonics Spectra, June 2009 Page 22 there is an article discussing the remote detection of life in soil. They look for characteristic chirality of scattered light from the samples. “Inorganic materials are a jumble of left- or right-handedness, and the resulting aggregate circular polarization is almost nonexistent.” “All known life on Earth, for example, uses only left-handed amino acids in proteins and right-handed sugars in nucleic acids.” This work is being done by the Space Telescope Science Institute and National Instititute of Standards and Technology and was presented in the Proceedings of the National Academy of Sciences in April.
You can use the viewing glasses you took from the 3D movie “Up”. They’re circularly polarized. ~

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