Earth or Mars?

Which image is Earth, and which is Mars? One of the above image s was taken by the robot Spirit rover currently climbing Husband Hill on Mars . The other image was taken by a human across the desert south of Morocco on Earth . Both images show vast plains covered with rocks and sand . Neither shows water or obvious signs of life . Each planet has a surface so complex that any one image does not do that planet justice . Understanding either one, it turns out, helps understand the other. Does the one on the left look like home? Possibly not, but it is Earth .