Final answer:
Earth's atmosphere has much less carbon dioxide compared to the atmospheres of Venus and Mars, which are composed of about 96 percent carbon dioxide.
Step-by-step explanation:
Compared to the atmospheres of Venus and Mars, Earth's atmosphere is much poorer in carbon dioxide (CO₂). Venus and Mars have atmospheres composed of roughly 96 percent carbon dioxide, while Earth's carbon dioxide levels are much lower due to its absorption in marine sediments and its transformation by photosynthetic life. On Earth, nitrogen is the most abundant gas in the atmosphere, making up approximately 78%, followed by oxygen, which accounts for about 21% due to the presence of life. Unlike Earth, the atmospheres of Venus and Mars are very dry with a near absence of water vapor.