Figure 1

This image mosaic made up of four images from the microscopic imager on the Mars Exploration Rover Opportunity shows a contact line between two distinct layers of rock (A and B in figure 1) inside "Endurance Crater." The layers are defined by subtle color and texture variations and represent separate chapters in Mars' history. Contact lines between the layers therefore represent periods of geologic time when significant environmental changes occurred. Data from Opportunity's scientific instruments indicate that both of the shown layers are rich in sulfates. Each microscopic image shows an area of about 3 centimeters by 3 centimeters (1.2 inches by 1.2 inches).