Unfortunately, we don’t know what the odds of life developing are given Earth-like conditions.

Probes like Kepler will indicate what those odds are. Kepler will tell us where planets and large moons are. Kepler’s descendants (and possibly Kepler itself) will tell us which of those planets and large moons have life-indicators such has high amounts of O2 in their atmospheres. It is only through such surveys that we can learn how frequently life occurs on worlds with Earth-like conditions.

That’s not correct. The key is in the term “earth-like.” Sure, if everything is exactly was as it was on earth when life developed – atom by atom, motion by motion – then the odds of life developing should be 100% give or take the quantum indeterminacy. But earth-like means similar to Earth in chemical composition, but not quite identical. We don’t really know what the odds of life developing are given those conditions. It could be everything from highly likely to so unbelievably unlikely as to be absurd. It’s all over the map. It’s a lottery where the odds of winning aren’t known. More lottery tickets could theoretically mean increasing the odds from infinitesimal to still infinitesimal.

A = [total years of X geologic conditions on earth]
B = [years before life with X geologic conditions]

Probability Estimate = 1 – [B/A]

We have evidence for cellular life within ~200 million years of the Earth’s crust solidifying.
I think something like that might be used as a dirty estimate for the probability of life (as we would recognize it) arising (somewhere like Earth).

[years before life with X geologic conditions] / [total years of X geologic conditions on earth] = [dirty estimate we could use to make predictions, tests, refinements.]

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There are 2 reasons moons are generally exciting for life.

1) Earth-like moons. Not Europa-like, or Titan-like, but Earth-like moons with the possibility of Earthish life.

2) Numbers. It might be more likely for Earth-like moons to form than Earth-like planets. But either way, existing at all raises the total odds for life. This is distinct from the excitement over extremophiles & Europa, which widen the range of “Earth-like”.