Over time, the movement of surface fluids has greatly changed Venus and Earth. A. Although Venus is about the same size as Earth, its greater volcanic activity has added considerably to carbon dioxide levels in its atmosphere. B. Like Venus, Earth has an atmosphere, but Earth's atmosphere has far more oxygen and nitrogen than does the atmosphere of Venus. C. On Earth, chemical reactions involving fluids remove carbon dioxide from the atmosphere by giving rise to carbonate rocks, and winds energized by gravity flow systems move fine particles from one place to another. D. Because Venus lost the water it originally had, most of its carbon dioxide remained in its atmosphere, causing the planet to become very warm. E. On Earth, the dominance of river valley landscapes and the existence of life are due to the planet's hydrologic cycle. F. The evaporation of liquid water from Earth's surface is largely limited by the life forms that have developed, particularly the vegetation.