Atmosphere Evolution on Rocky Planets
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 different condition that causes the formation of current atmosphere. This essay will focus on the evolution of atmosphere on Earth, Venus, and Mars and compare the current atmospheric conditions of these planets. Furthermore, how the Earth’s atmosphere can sustain life and how life on earth affect Earth’s atmosphere over different period of time will also be discussed. First of all, there are some changes happenned in atmospheric condition of Venus over time. Venus has a very thick and dense atmosphere which mostly consists of carbon dioxide . This carbon dioxide rich atmosphere is approximately 100 times greater than in Earth’s atmosphere . The carbon dioxide trap infrared radiation originated from the Sun and bounced back from the planet surface, and causes large-scale greenhouse gas effect. This condition makes the Venus’ surface to be very hot (above 450C). Experts believe that significant volume of water was covering the surface of the planet at the early stage . However, combinations of Venus location relative to the sun as well as the global warming condition evaporate the vast ocean on the Venus’s surface in a very short geological timescale . Some of this water vapor then combined with the sulfur dioxide released by volcanic to become H2SO3 (sulfuric acid) droplets while the rest is broken down by photons and swept by solar wind. Complete removal of water due to this extreme condition stops geological and biological evolution . On the contrary to Venus, Mars is relatively far from the Sun and thus it has colder temperature compared to both Venus and Earth . Mars also has smaller mass and size than Venus and Earth, which result in weaker gravitational force necessary to hold atmospheric gas in place. This planet also does not have a magnetic field . The combination of weak gravitational force as well as no magnetic field contributes to the instability of atmosphere from the solar winds and thus result in a very low atmospheric pressure in Mars. Low temperature in Mars make the water frozes, and the low atmospheric pressure ensures that the escaped water molecule turns into vapour instead of liquid. In other words, the water in Mars is either frozen or evaporated . This condition leads to thin, cold, and dry atmosphere, which only contains trace of water vapor . Lastly, Earth’s atmospheric evolution starts from around 4.5 billion years ago where dimmer Sun, greenhouse gas-rich, and oxygen-poor condition affecting earth’s atmosphere and early ocean. The dimmer Sun supplied less solar radiation, which is important to provide heat to the Earth surface. Since the intensity of solar radiation from Sun was less to warm the early Earth, the presence of much higher atmospheric ‘greenhouse’ helped to keep the surface warm enough to maintain water in liquid form. The temperature increases was about 30C above freezing point of water, which makes the out-gassed water remains liquid. The earth also has an active core, which presents a strong magnetic field to counter the Solar wind and maintain the Earth atmosphere pressure . Table below shows the comparison of various variables affecting atmospheric conditions on the Venus, Earth and Mars. Table 1. Basic...
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