سؤال قراءة ستيب محلول — الاستنتاج (تدريب 5157)

(1) Today Mars have only a thin atmosphere and its surface is very dry with the possible exceptions of some localized and temporary water seeps. However, ancient eroded valley networks that were discovered by orbiting space. Craft in the early days of exploration prove that water flowed across the surface in the remote past. (2) The nature of the oldest valley, which have many tributaries, shows that the water was most likely supplied by rainfall. This means the surface was very likely habitable for life back then. (3) When clay minerals were detected from orbit and subsequently confirmed by surface ravers; it was taken as further evidence that mars once had a wet surface environment, hospitable life. This is because when most rocky minerals decay under humid conditions they rot to form various kinds of clay. (4) Clay minerals cannot form unless there is water available, it is essential ingredient in their microscopic crystalline structure. Clays are found virtually nowhere and the red planet except in Mars most ancient terrains, dating back to an period about 3.7-4.1 billion years ago, called the Noachian. (5) On earth, clay forms by minerals grains that are chemically attacked by water. Most scientists believe that a similar process took place on Mars during its wet, Noachian period. However, some researchers have suggested that most of the detected clay was not formed in this way at all. They argued instead it formed prior to that, while warm water was circulating through the bedrock in response to nearby volcanic and instructive activity.