Atmosphere can be defined as a gaseous compound layer surrounding a large body mass suspended by means of gravity and centrifugal force caused by rotation . Atmospheres of planets have not always been the same, its evolution comprised of complex development across million years of geologic time affected by various changes of variables inside and outside its planet . Of the interest of this essay is the atmospheric evolution of a rocky planet. Rocky planet is a terrestrial body consists mainly of silicate or metal . Some known rocky planets with substantial atmosphere such as Venus, Mars and Earth has a very different composition of atmospheric gas . These planets experienced very …show more content…
Compare to the other two planets, Venus does not have water in any forms due to the greenhouse gas effects as well as its relative distance to the Sun, which evaporates all the available water in any form on its surface. This is shown on the Figure 1 above, that water can only form as a gaseous compound on Venus surface, this water vapor then combined with the SO2 from volcanic out-gassing to create sulfuric acid clouds.
For Earth and Mars, water exists as a different form in their surfaces. Figure 1 shows the different phases of water as a function of temperature and pressure of the planet. Earth is shown to have high pressure and temperature that allows the presence of water in solid, liquid, and vapor phases. Mars has low pressure and low temperature, thus allowing the water to be stable only in solid and vapor phase. This planet is shown to be located close to the triple point, thus the little increase of temperature and pressure for short period of time allows ice to form liquid water. Venus is shown to be present in vapor phase due to the high atmospheric temperature and pressure .
Life was developed in the Earth due to the presence of liquid water. The existence of plants and some photosynthetic bacteria utilize CO2 and yield O2. Furthermore, water washes and deposits CO2 as minerals into the oceans. It leaves small amount of carbon dioxide at the atmosphere (0.038%). Therefore, the composition of CO2