Venus has the densest atmosphere of all the terrestrial planets, consisting mostly of carbon dioxide, as it has no carbon cycle to lock carbon back into rocks and surface features, nor organic life to absorb it in biomass. It has become so hot that the earth-like oceans the young Venus is believed to have possessed have totally evaporated, leaving a dusty dry desert scape with many slab-like rocks. The evaporated water vapor has dissociated and hydrogen has escaped into interplanetary space. The atmospheric pressure at the planet's surface is 92 times that of the Earth, the great majority of it carbon dioxide and other greenhouse gases. Venus's surface has been mapped in detail only in the last 20 years Project Magellan listed about a thousand meteor craters, a surprisingly low number compared to Earth. It shows evidence of being geologically very young with extensive volcanism, and the sulfur in the atmosphere is taken by some experts to show many of its volcanoes are still active today, but it is an enigma as to why no evidence of lava flow accompanies any of the
