Miyamoto Crater is just west of the Plains of Meridiani. A huge hole in the ground, the crater is 150 kilometers (93 miles) wide. Rocks formed in the presence of water fill the crater's northeastern half. Like those discovered by the Opportunity rover, they include minerals of iron and sulfur. These materials likely settled on lake bottoms or in groundwater systems. In the southwestern portion of the crater floor, erosion has stripped them away. The eroded surfaces are windows into the very remote past. They reveal clays and other materials like those found in the most ancient Martian rocks. More than 3.5 billion years old, they date to the Noachian era. At that time, liquid water was likely present at the surface. Perhaps the water created an environment favorable to life.