What specific geological features suggest Mars historically held liquid water on its surface?
Answer
Ancient river valleys, flood channels, and sedimentary rock layers.
Evidence supporting the historical habitability of Mars rests heavily on interpreting its ancient surface geology. Scientists observing the planet noted clear topographical features that strongly resemble terrestrial formations created by flowing water. Specifically, the existence of ancient river valleys and extensive flood channels indicates periods when massive amounts of liquid water moved across the surface. Furthermore, the identification of sedimentary rock layers implies that materials were deposited and compacted under the presence of a fluid medium, most likely water, during a time when the planet was significantly warmer and wetter than its current arid state.
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