Colonization of Titan Zubrin has pointed out that Titan possesses an abundance of all the elements necessary to support life, saying "In certain ways, Titan is the most hospitable extraterrestrial world within our solar system for human colonization." The atmosphere contains plentiful nitrogen and methane, and strong evidence indicates that liquid methane exists on the surface. Evidence also indicates the presence of liquid water and ammonia under the surface, which are delivered to the surface by volcanic activity. Water can be used to generate breathable oxygen and nitrogen is ideal to add buffer gas partial pressure to breathable air (it forms about 78%
Atmosphere of Venus to have had a Venus-like atmosphere, with roughly 100 bar of CO and a surface temperature of 230 °C, and possibly even sulfuric acid clouds, until about 4.0 billion years ago, by which time plate tectonics were in full force and together with the early water oceans, removed the CO and sulfur from the atmosphere. Early Venus would thus most likely have had water oceans like the Earth, but any plate tectonics would have ended when Venus lost its oceans. Its surface is estimated to be about 500 million years old, so it would not be expected to show evidence