Two observed features on Mars appear to lead to contrary geological conclusions-the appearance of massive, solitary volcanoes, apparently caused by hot spots under the planet's surface, and the discovery of a long, deep rift valley across the planet. Why are the two features a contradiction?

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Massive, solitary volcanoes on Mars suggest the presence of stationary hot spots beneath the planet's surface, a feature typically not associated with the movement of tectonic plates. On the other hand, the existence of a long, deep rift valley suggests the presence of tectonic activity, as such valleys are often formed by the stretching and breaking apart of the Earth's crust, a process linked to plate tectonics. These two features seem contradictory because one implies a lack of plate tectonics (hot-spot volcanism) while the other suggests tectonic activity (rift valley formation).

Two Observed Features on Mars Appear to Lead to Contrary