Venus is a planet in our system on which conditions are closer to hell than to paradise with a cloudy envelope of sulfuric acid and a rocky surface whose heat is high enough to melt any metal there instantly.
However, if Venus is today dry and hot, it was able, at some point in its past, to offer oceans as on Earth. Ancient studies have hypothesized that Venus has had enough water in its atmosphere in the past to have been completely covered by an ocean 25 meters deep.
This hypothesis is now revised, and scientists now believe that if it weren't for an ocean of water, it would be oceans of liquid carbon dioxide that would have shaped the surface of the planet.
Currently, carbon dioxide represents 96.5% of the atmosphere of Venus. Under certain conditions of pressure and heat, carbon dioxide can reach a supercritical state, offering it the combined properties of a liquid and a gas.
The atmospheric pressure of Venus is 90 times higher than that of the Earth, but in its childhood, the pressure could be up to twelve times higher still, during a period going from 100 to 200 million years. Under these conditions, it is possible that supercritical carbon dioxide has formed and that these oceans have hollowed out valleys and canyons on the surface of the planet.