Earth ozone layer due to the subsequent conversion of atmospheric into. The ozone layer blocks ultraviolet solar radiation, permitting life on land. Other atmospheric functions important to life include transporting water vapor, providing useful gases, causing small meteors to burn up before they strike the surface, and moderating temperature. This last phenomenon is known as the greenhouse effect: trace molecules within the atmosphere serve to capture thermal energy emitted from the ground, thereby raising the average temperature. Water vapor, carbon dioxide, methane, nitrous oxide, and ozone are the primary greenhouse gases in the atmosphere. Without this heat-retention effect, the average surface
Venus the atmospheric pressure is ninety times that of Earth, and the extreme impact of the greenhouse effect, make water-based life as we know it unlikely. A few scientists have speculated that thermoacidophilic extremophile microorganisms might exist in the lower-temperature, acidic upper layers of the Venusian atmosphere. The atmospheric pressure and temperature fifty kilometres above the surface are similar to those at Earth's surface. This has led to proposals to use aerostats (lighter-than-air balloons) for initial exploration and ultimately for permanent "floating cities" in the Venusian atmosphere. Among the many engineering challenges are the dangerous amounts of sulfuric acid at these