Venus is currently drier than a bone. But the high deuterium ratio in the atmosphere hints at isotopic fractionation of a LOT of water in the deep past. Enough for a shallow ocean, or perhaps a deeper one with a bit of tweaking. That’s uncontroversial in most planetological discussions, but what is difficult to determine is just how long that primal ocean lasted for. David Grinspoon and Mark Bullock have suggested strongly that clouds would allow an ocean to last at least a billion years or two, making Venus habitable much longer than previous estimates of a mere 0.5 billion years. In that time enough oxygen might have accumulated from dissociation to give life an oxygenic head-start…
Did Venus’s ancient oceans incubate life? – space – 10 October 2007 – New Scientist Space
…theoretically spores from microbes can be lofted into space electromagnetically and because Venus has no observed magnetic field the atmosphere interacts directly with the solar wind. Life could then be blown outwards to Earth, Mars and even a wet, warm early Titan.
