Passage VI

In the Chryse Planitia area of Mars's surface, numerous winding channels are visible. The channels, some of which are 100 km long, were formed more than 3 billion years ago (bya). Two scientists discuss whether these channels were formed by liquid H2O or by liquid CO2.

Scientist 1

Unlike today, Mars was warm enough prior to 3 bya for liquid H2O to exist on the surface. Prior to the formation of the channels, a large volume of liquid H2O slowly accumulated in a basin within the Chryse Planitia. Once the volume became great enough, the liquid H2O was released suddenly from the basin. The rapidly flowing liquid H2O carried away rocks and soil, forming the channels. On Earth, similar features called outflow channels are produced by the sudden release of a large volume of liquid H2O from a basin.

Grey hematite (a mineral) is abundant on Mars's surface within the Chryse Planitia. On Earth, this mineral is associated exclusively with liquid H2O . Even today, large quantities of frozen H2O are still present in Mars's polar regions.

Scientist 2

Before 3 bya, large volumes of CO2 gas were present a short distance below the surface in the Chryse Planitia. Eventually, the subsurface pressure due to the weight of the overlying rocks and soil became great enough to change the CO2 to a liquid. When a later major event such as an asteroid impact removed most of the overlying material, the liquid CO2 quickly moved up to and then along the surface. The rapidly flowing liquid CO2 carried away rocks and soil, forming the channels. On Earth, gases or liquids that have been under pressure belowground are released to the surface during some volcanic eruptions. These pyroclastic flows move rapidly along the ground, forming channels by carrying away rocks and soil.

Since Mars's formation, its average surface temperature has never been greater than -50°C. This has made it impossible for a significant amount of liquid H2O to be present on the surface. If any liquid H2O had been present on Mars's surface, it would have reacted with CO2 to produce carbonate rock (a rock composed of carbonate minerals). No carbonate rock has been found on Mars.

39. Suppose liquid H2O was present on Mars's surface prior to 3 bya. Would Scientist 1 agree that grey hematite might have been present on Mars' s surface prior to 3 bya, and would Scientist 2 agree that carbonate rock might have been present on Mars's surface prior to 3 bya?

Answer and Explanation

Your Answer is

Correct Answer is A

Explanation

Look at the second paragraph of Scientist 1, which says that gray hematite can only be formed in the presence of liquid water, so there is indeed liquid water on Mars, so there should be gray hematite;

Look at the fourth line of the second paragraph of Scientist 2. The scientist believes that if there is liquid water on Mars, then the liquid water will form carbonate rock with CO2.

So option A meets