Read this excerpt from "Mars: Landscape of the Red Planet." In addition to its volcanic landscape, Mars also has an amazing system of canyons known as the Valles Marineris. Scientist have ruled out water as the reason for the formation of these canyons. Instead, they theorize that the canyons were formed from the splitting of the Martian crust due to the cooling of the planet. Valles Marineris runs 2,500 miles long at a depth of 4 miles, dwarfing the Grand Canyon back on Earth, which is only 500 miles long and 1 mile deep.

Canyons on Mars appear to have been formed by the splitting of the Martian crust. However, canyons on Earth were most likely formed by

the impact of asteroids causing damage to the surface.
water flowing through rivers over long periods of time.
earthquakes causing parts of Earth’s crust to rise up.
the rising of hot magma from deep inside Earth’s core.