venus's atmosphere has much more carbon dioxide than earth's because
Atmosphere of Venus Unlike Earth, Venus lacks a magnetic field. Its ionosphere separates the atmosphere from outer space and the solar wind. This ionised layer excludes the solar magnetic field, giving Venus a distinct magnetic environment. This is considered Venus's induced magnetosphere. Lighter gases, including water vapour, are continuously blown away by the solar wind through the induced magnetotail.[4] It is speculated that the atmosphere of Venus up to around 4Â billion years ago was more like that of the Earth with liquid water on the surface. A runaway greenhouse effect may have been caused by the evaporation of the surface water and subsequent rise of the levels of other greenhouse gases.[8][9]