Valles Marineris, the great canyon of Mars that stretches for more than 2,500 miles (4,000 kilometers) and is up to 4.3 miles (7.0km) deep, formed as the martian lithosphere spread apart early in the Red Planet’s history. The lithosphere is the solid, uppermost portion of the planet that sits above the partly molten mantle. The martian lithosphere is approximately 120 miles (200km) thick — much thicker than Earth’s. This cold lithosphere has a great deal of strength and can hold up the large martian volcanoes such as Olympus Mons.
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