2. This photograph shows channels in the sand on Mars and suggests that water created them. It also shows a picture if a water channel on Earth and the two channels are very similar.

3. River Valleys such as this one on Valles Marineris resemble a river-cut valley. The picture shows the direction of the flow and tributaries to the river.

4. Valles Marineris Valles Marineris Different sedimentary rock layers have been found on Mars similar to this one on Holden Crater. These layers suggest that this area was once a lake.

5. “MOC Images Suggest Recent Sources of Liquid Water on Mars.” Mars Global Surveyor Mars Orbiter Camera (MOC). 22 June 2000. Malin Space Science Systems. 3 April 2002. “The Case of the Missing Mars Water.” Mars Exploration. 5 January 2001. 3 April 2002.