As an expert in the field of planetary science, I'm delighted to share insights about the composition of planetary atmospheres. The planet that predominantly features an atmosphere of carbon dioxide is Venus. Venus, often referred to as Earth's "sister planet" due to its similar size and proximity, has an atmosphere that is approximately 96.5% carbon dioxide, with the remaining percentage being nitrogen and trace amounts of other gases.

The atmosphere of Venus is not only rich in carbon dioxide but also exhibits a high surface pressure, about 90 times that of Earth's, and a surface temperature that averages around 735 Kelvin (462 degrees Celsius), making it the hottest planet in our solar system, even hotter than Mercury, which is closer to the Sun. This extreme heat is largely due to the Greenhouse Effect, a process where the atmospheric gases trap heat and prevent it from escaping into space.

The composition of Venus's atmosphere is a result of volcanic outgassing and chemical reactions over geological time. Unlike Earth, which has a carbon cycle that includes processes like photosynthesis and respiration that help regulate atmospheric carbon dioxide levels, Venus lacks such mechanisms. The high levels of carbon dioxide have led to a runaway greenhouse effect, exacerbating the planet's warming.

In contrast, the gas giants, such as Jupiter and Saturn, have atmospheres that are primarily composed of hydrogen and helium. These planets are much larger than the inner rocky planets like Earth and Venus, and their atmospheres are characterized by different physical and chemical processes.

The early atmospheres of the inner planets, including Earth and Venus, have indeed evolved since their formation. Earth's original atmosphere is believed to have been similar to that of Venus, rich in carbon dioxide and nitrogen. However, the evolution of life on Earth and the development of its carbon cycle have significantly altered the composition of our atmosphere, leading to the presence of oxygen, which is virtually absent in Venus's atmosphere.

Understanding the differences in atmospheric composition and the processes that shape them is crucial for comparative planetology, which helps us learn more about the potential for life elsewhere in the universe and the factors that influence planetary habitability.

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VenusIn contrast, the gas giant atmospheres are composed mostly of hydrogen and helium. The atmospheres of at least the inner planets has evolved since they formed. This is clearest for the Earth. The Earth's original atmosphere was probably similar to Venus in composition, consisting of carbon dioxide and nitrogen.read more >>