Today, there are rumors about an upcoming announcement of the discovery of (non-conclusive) evidence for life on Venus, apparently they detected some phosphorus compound that is not produced by any known abiotic chemistry, but is produced by terrestrial bacteria.

Of course, the more parsimonious explanation is that there is some abiotic chemistry that produces this phosphorus compound, and we just don't know of it.

It occurs to me that this is not the first time this happened: the Viking landers' labeled release experiment on Mars also gave a positive result, and as I understand it, some of the people involved maintain to this day that it actually detected life. Again, the standard explanation involves a hypothetical abiotic process.

One might tell a similar tale about the fossilized bacteria in meteorites from Mars.

Now, I do not doubt that in most or all cases the abiotic explanation is correct. But there seems to be a pattern here. How often has this happened? How many more examples are there of claimed signs of life in space being dismissed as being caused by poorly understood abiotic processes?

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    $\begingroup$ You've certainly listed the first ones that came to mind. Interesting question! $\endgroup$ Sep 14 '20 at 17:30
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    $\begingroup$ In the case of Venusian phosphine, the mystery is they've tried abiotic models such as volcanic emission and can't account for all of what is seen. Thus The Question persists. $\endgroup$ Sep 14 '20 at 19:50
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    $\begingroup$ The one thing that works against a biotic source of the phosphine in the atmosphere of Venus is the amount of sulfuric acid in the atmosphere. The clouds are composed of 75 to 95 percent sulfuric acid, "which is catastrophic for the cellular structures that make up living organisms on Earth". Phosphine gas in the cloud decks of Venus $\endgroup$
    – Fred
    Sep 14 '20 at 20:30
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    $\begingroup$ Carl Sagan was one of the first to suggest microbes may be able to live in the clouds of Venus. He also came up with the quote "extraordinary claims require extraordinary evidence" $\endgroup$ Sep 15 '20 at 13:55
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    $\begingroup$ This could be extended to the work of paleontologists & Terran artifacts as well. Granted we know life exists here :-) but just when and what types appeared at what point in history are semi-open questions. $\endgroup$ Sep 15 '20 at 14:18

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