Worlds in Collision
Tim Callahan, religion editor of "Skeptic", presses the case further in claiming that the composition of the atmosphere of Venus is a complete disproof of "Worlds in Collision". "...Velikovsky's hypothesis stands or falls on Venus having a reducing atmosphere made up mainly of hydrocarbons. In fact, the atmosphere of Venus is made up mainly of carbon dioxide—carbon in its "oxidized" form—along with clouds of sulfuric acid. Therefore, it couldn't have carried such an atmosphere with it out of Jupiter and it couldn't be the source of hydrocarbons to react with oxygen in our atmosphere to produce carbohydrates. Velikovsky's hypothesis is falsified by the carbon dioxide atmosphere of Venus."
Secondary atmosphere
A secondary atmosphere is an atmosphere of a planet that did not form by accretion during the formation of the planet's star. A secondary atmosphere instead forms from internal volcanic activity, or by accumulation of material from comet impacts. It is characteristic of terrestrial planets, which includes the other terrestrial planets in the Solar System: Mercury, Venus, and Mars. Secondary atmospheres are relatively thin compared to primary atmospheres like Jupiter's. Further processing of a secondary atmosphere, for example by the processes of biological life, can produce a tertiary atmosphere, such as that of Earth.