Look here in the blog’s archives for the article that accompanies this picture. History Moments, January 30, 2010.
Top Picture: Landsat satellite picture of the Sahara Desert
Bottom Picture: Rock layer underneath, revealing black channels cut by the meandering of an ancient river. Taken by Spaceborne Imaging Radar-C/X-band Synthetic Aperture Radar (SIR-C/X-SAR) on board the Space Shuttle Endeavour on April 16, 1994.