The atmosphere of Venus is quite different from ours. Measurements taken om the Earth show a high
concentration of carton dioxide in the atmosphere of Venus. In fact, carbon dioxide makes up 96 percent of
Venus' atmosphere; trogen makes up almost all the rest. The Earth's atmosphere, by comparison, is mainly
nitrogen, with a fair amount of oxygen as well. Carbon dioxide makes up less than 0.1 percent of the terrestrial
atmosphere.
The surface pressure of Venus' atmosphere is 90 times higher than the pressure of the Earth's atmosphere, as a
result of the large amount of carbon oxide in the former. Throughout Earth's history, carbon dioxide on Earth
has fixed with rain to dissolve rocks; the dissolved rock and carbon dioxide eventually flow into the oceans,
Luyện Thi Đại Học 2010 Khối D (9) ~ 3
where they precipitate to form new terrestrial rocks, often with the help of life-forms. If this carbon dioxide
were released from the Earth's rocks, along with lower carbon dioxide trapped in seawater, our mosphere would
become as dense and have as high a pressure as that of Venus. Venus, slightly closer to the Sun than Earth and
thus hotter, had no oceans in which carbon dioxide could dissolve or life to help take up the carbon.
Also, Venus has probably lost almost all the water it ever had. Since Venus is closer to the Sun than the Earth
is, its lower atmosphere was hotter even early on. The result was that more water vapour went into its upper
atmosphere, where solar ultraviolet rays broke in up into hydrogen and oxygen. The hydrogen, a light gas,
ecaped easily; the oxygen has combined with other gasses or with iron on Venus' surface.
Studies from the Earth show that the clouds on Venus are primarily composed of droplets of sulfuric acid, with
water droplets mixed in. Sulfuric acid may sound strange as a cloud constituent, but the Earth too has a
significant layer of sulfuric acid droplets in its stratosphere. However, the water in the lower layers of the Earth's
atmosphere, circulating because of weather, washes the sulfur compounds it out of these layers, whereas Venus
has sulfur compounds in the lower layers of its atmosphere in addition to those in its clouds.