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

Question

Quizplus · Accepted Answer

The carbon dioxide on Earth is primarily locked up in sedimentary rocks such as limestone. These rocks are formed from the skeletal remains of marine organisms that have absorbed CO2 from the atmosphere and ocean to build their shells and skeletons. Over millions of years, the accumulation of these remains has led to the sequestration of large amounts of carbon dioxide in the Earth's crust, significantly reducing the amount of CO2 in the atmosphere compared to Venus and Mars.

One of the Major Differences Between Earth and Its Neighboring