I was wondering, if we measured the carbon isotopic ratio of methane on Mars and found that it was very negative (i.e. it contained more carbon-12 than carbon-13), would this provide definitive proof that life exists on Mars.

  • $\begingroup$ Bell you need to considere there is an abiotic C cycle wich invloves the hole C and atmospheric CO2-CH4 transfers. I guess NASA is not notizing special isotopic composition of Mars atmosphere because it has the common isotopic relation on the hole Solar System. A proof of life would be a punctual measure of some CH4 mollecules, probably at soil as you noticed at another post that were rich in C12 and poor in C14 because an organic origin $\endgroup$
    – user12525
    Oct 15 '18 at 15:54
  • $\begingroup$ There is not biotic intervention in that transfers. On Earth's atmosphere you don't see CO2 has heavy C and CH4 ligth mollecules. You would see that on methane compounds on ocean soil as formed by decomposition of organic matter. All organic matter has ligthweigth high C concentrations but atmospheric measures on the hole planet only shows the common solar system relation c14/c12 $\endgroup$
    – user12525
    Oct 15 '18 at 15:59
  • $\begingroup$ When we search for life on Mars, are looking at the ratio c14:c12 or c13:c12? $\endgroup$
    – Bell
    Oct 17 '18 at 23:35
  • $\begingroup$ My guess is C13/C12. C14 is trace and, I cannot affirm it (I don't work on,etc...), but my sense says the signal will be clear for C13/C12, not so for C14. I found this text talking about dating with C14. Look at this paragraph. I didn't know C14 was formed on atmosphere by the way, wich is related with your interest on the topic. Hoppe helps $\endgroup$
    – user12525
    Oct 18 '18 at 2:52
  • $\begingroup$ "There are three principal isotopes of carbon which occur naturally - C12, C13 (both stable) and C14 (unstable or radioactive). These isotopes are present in the following amounts C12 - 98.89%, C13 - 1.11% and C14 - 0.00000000010%. Thus, one carbon 14 atom exists in nature for every 1,000,000,000,000 C12 atoms in living material. The radiocarbon method is based on the rate of decay of the radioactive or unstable carbon isotope 14 (14C), which is formed in the upper atmosphere through the effect of cosmic ray neutrons upon nitrogen 14. " c14dating.com/int.html $\endgroup$
    – user12525
    Oct 18 '18 at 2:52

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