Eventually, part of the water rose to the surface and escaped through cracks and fissures in the earth's crust. This water slowly accumulated in the natural basins of the crust that make up the modern oceans. Similar events should have occurred on Venus over the past 4.5 billion years, the assumed age of the earth, and as a result some water should now cover the surface of Venus. Because of the extremely high temperature of the Venusian surface, however, the water would not be present as a liquid but in the form of vapor in the atmosphere.
Earth-based spectroscopic studies had indicated the presence of carbon dioxide in the Venusian atmosphere. Soviet and U.S. spacecraft results showed this to be the case. Venera 4 gave a reading of 90-95% of carbon dioxide at an altitude of 25 km (15.5 mi), while Mariner 5 indicated 69-87% at 60 to 70 km (37 to 43.5 mi). The amount of carbon dioxide in earth's atmosphere is less than 1%. Negligible amounts of oxygen and water vapor appear to be present in the Venusian atmosphere, and nitrogen—a large component of earth's atmosphere—was not detected.
Radar techniques also permit mapping of the moon and the nearer planets, a method especially useful in the case of cloud-shrouded Venus. Cornell University scientists at the Arecibo Observatory in Puerto Rico had mapped a third of the Venusian surface by early 1968. They found rough areas near the equator and what appeared to be mountains in the planet's southern hemisphere.
Eventually, part of the water rose to the surface and escaped through cracks and fissures in the earth's crust. This water slowly accumulated in the natural basins of the crust that make up the modern oceans. Similar events should have occurred on Venus over the past 4.5 billion years, the assumed age of the earth, and as a result some water should now cover the surface of Venus. Because of the extremely high temperature of the Venusian surface, however, the water would not be present as a liquid but in the form of vapor in the atmosphere.