Okay, here's what I told folks who asked about the detection of phosphine (PH3) in the atmosphere of Venus: If you give me the options of unknown chemistry, unknown geology, or unknown biology, then biology is always going to be a distant third behind the other two options.

We see phosphine in other places in the solar system, and it's not biological. Now, terrestrial planets are not the same as gas giants, for sure! But I think we're a ways away from ruling out chemistry and geology as sources of phosphine.

And honestly, with an extraordinary claim like extraterrestrial life, you do have to 100% rule out every other possible origin.

Here's the terribly poorly-kept-secret article! https://twitter.com/NatureAstronomy/status/1305522642590588934?s=20

Oh and here is a good thread by @PlanetDr (whose job it is to actually measure chemical reactions and compositions under planetary atmosphere conditions) with some more context for why it's hard to know all the ways phosphine might come to be: https://twitter.com/PlanetDr/status/1305479161218293760?s=20

I do want to say, having read the paper, I believe the authors did as thorough a job as they were able analysing the data and discussing the possibilities.

Here's the final paragraph of the discussion, since the paper is still inexplicably paywalled.

Ah, @ProfAbelMendez has found the paper available online via @ESO's website:

https://www.eso.org/public/archives/releases/sciencepapers/eso2015/eso2015a.pdf