One of the Major Differences Between Earth and Its Neighboring

question 149

Multiple Choice

One of the major differences between Earth and its neighboring planets Venus and Mars is the lack of large quantities of carbon dioxide in its atmosphere near the surface of the planet. If all these planets were originally formed with significant quantities of this gas in their atmospheres, where is this carbon dioxide on Earth at the present time?

• A) concentrated high in the atmosphere, where it contributes to the greenhouse effect
• B) dissociated by solar UV light into carbon and oxygen, which now exist in abundance as separate chemicals
• C) locked up in rocks such as limestone, formed by life-forms in the sea and on Earth's surface
• D) dissolved in seawater, a situation that cannot arise on Venus or Mars