Strategies to search for life on exoplanets include looking for evidence of atmospheric O2 because the accumulation of O2 in Earth's atmopshere was driven by oxygenic photosynthesis. Substantial attention has been given to determining the conditions that could give rise to "false positives"—i.e., the presence of significant atmospheric O2 in the absence of biology. Comparatively little attention has been given to the conditions that could give rise to "false negatives"—i.e., the absence of atmospheric O2 despite the presence of extensive oxygenic photosynthesis. On such worlds, life may be very abundant but not easily detectable. The geologic record reveals that Earth itself would have been a "false negative" world for much of its history and so the latter possibility must be seriously considered. Given the extensive telescope time that will be needed to detect O2 if it is present, there is great value in finding ways to determine a priori which planets are likely to be false negatives even if O2 is being produced. This talk will review the geologic evidence of Earth's past, the condiitions that may produce false negatives, and the gaps in our understanding that must be filled in order to determine which planets are the best bets for detecting life if it is there.

Avoiding "false negatives" in the search for life on other worlds: Lessons from ancient Earth

2019 Spring National Meeting

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