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Venus possibly habitable for billions of years
This also suggests that another global transformation on Venus about 700 million years ago, in which the whole planet's surface appears to have melted and reformed, may actually have been a continuation of the same greenhouse warming that dried out the planet.
Once the water was lost, Grinspoon says, plate tectonics would have stopped completely, and with it the most efficient way for the planet to shed its internal heat. This could have led to a buildup that eventually caused the whole crust to melt and then reform.
More generally, if this analysis is right, it means that the "habitable zone" for planets around other stars may be much wider than has been assumed, since Venus had been thought to be far outside it.
�New Scientist 09.08.03