Did Venus have a habitable stage?
First, the presence of elements like hydrogen, which is very light and escapes much more easily from the atmosphere of a planet with as much deuterium as Venus, indicates that this world once had a lot of hydrogen, which it was probably connected to the water.
If the model is correct, Venus could have been more temperate and have liquid water lakes and oceans. It also suggests that the planet closest to Earth in size and distance from the Sun could not only have oceans, but also could have survived for over 1 billion years, the oceans that existed when there was already life on our planet. Thus, it may be unlikely, but not impossible, that there is a large potential overlap with the age of life on Earth.
At most, Venus would have enough water to cover its entire surface to a depth of 500 meters (on a flat surface), but would have featured large ocean basins and exposed land.
In any case, we are limited by the data we have on Venus. If all goes well, that will change soon. Thanks to two NASA missions, VERITAS and DAVINCI, that together with the mission InVision of the European Space Agency, will bring us a little closer to the reality of this infernal twin of the Earth.
Life on Earth is believed to have started around 3.5 to 4 billion years ago based on the fossil record. If Venus had liquid water on its surface 3 billion years ago, it could also have harbored life.
Could Earth follow the same path as Venus in the future? Understanding their history can help us determine the future of ours.
Alexandra O. Warren et al, Narrow range of early habitable scenarios for Venus allowed by modeling oxygen loss and radiogenic argon outgassing, Proceedings of the National Academy of Sciences (2023). DOI: 10.1073/pnas.2209751120
M. Turbet et al. 2021. Day-night cloud asymmetry prevents the first oceans on Venus, but not on Earth. Nature 598, 276-280; doi: 10.1038/s41586-021-03873-w