Martian landscapes and landforms indicate episodic activity by water and ice, extending from the planet's earliest history up to the present day. Most of the relevant fluvial, glacial, volcano-ice, periglacial, lacustrine (even “marine”), and related landforms have direct counterparts on Earth. Moreover, they exist in causally related, holistic associations of space and time that confirm their relationship to a long-term history of water-related activity. Although strong geomorphological evidence for many of these relationships has been apparent for 30 years, its scientific importance has only been recently appreciated because of direct geochemical measurements of water and ice features by surface robotic and orbital instruments.

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