ocr: l . - n MARS AND EARTH: A COMPARATIVE HISTORY The EARC a problem of Mars (cont.) Volcanic activity o Mars undoubtedly produced an atmosphere composed of carbon dioxide and water vapor. The resulting greenhouse effect probably raised the temperature on the surface above the freezing point. Soiti is possible that at one time rain fell on the Red Planet, that rivers and even lakes formed. But these phenomena did not last. Since the gravity on Mars is one-third that on Earth, the Red Planet could not hold its atmosphere. All the water vapor eventually escaped, as did the carbon dioxide to a lesser ...
