As a follow up note here, the arxix paper,
https://arxiv.org/ftp/arxiv/papers/2009/2009.06499.pdf
[1. 1. 2. Phosphine is Exclusively Associated with Life on Earth On Earth phosphine is a gas exclusively associated with life and is not made by any other natural atmospheric or geological chemical process (see e.g. (Gassmann and Glindemann 1993; Glindemann et al. 2003; Glindemann et al. 2005a; Glindemann et al. 1996)) and reviewed in (Bains et al. 2019a; Bains et al. 2019b; Sousa-Silva et al. 2020)). Terrestrial phosphine fulfils the criteria for being a biosignature gas, a gas whose detection indicates the presence of life (Catling et al. 2018; Seager and Bains 2015; Seager et al. 2016; Sousa-Silva et al. 2020; Walker et al. 2018). Previous work predicted that, if detected on a temperate rocky planet, phosphine is a robust biosignature gas due to spectroscopic potential and limited false positives in such environments, although detection is extremely challenging (Sousa-Silva et al. 2020). Since phosphine is mostly studied in the context of industrial chemistry, agriculture and laboratory chemical synthesis, its biology is not widely known. This warrants a brief introduction on the chemistry and biology of phosphine in the context of its biosignature potential on rocky planets.
1. 2. Motivation
Detection of phosphine in the atmosphere of Venus is completely unexpected. If the detection is confirmed by further observations, the presence of phosphine in Venus’ atmosphere suggests that our understanding of Venusian atmospheric chemistry is at least incomplete, and that the source of that phosphine needs to be identified. In light of the exclusively biological production of phosphine on Earth, the only rocky planet hitherto known to have phosphine in its atmosphere, the question arises whether the detection of phosphine on Venus could indicate the presence of life. For such a claim to even be entertained, all other possible sources of phosphine must be identified and eliminated. We emphasize that, even if the detection of phosphine is confirmed in the atmosphere of Venus, this can only be considered as evidence of the presence of life if all other sources of phosphine can be ruled out (Catling et al. 2018). This paper is a first step in that undertaking, considering possible non-biological mechanisms for making phosphine in the atmosphere, surface or subsurface of Venus.]
I note, "For such a claim to even be entertained, all other possible sources of phosphine must be identified and eliminated." Okay, a very good approach to science before Venus can be claimed to have life today.