Astronomy Picture of the Day . ... Credit: Landsat 7 , USGS , NASA Explanation: What on Earth is that? ... Once thought to be an impact crater , the Richat Structure 's flat middle and lack of shock-altered rock indicates otherwise. ... Rather, the layered sedimentary rock of the Richat structure is now thought by many to have been caused by uplifted rock sculpted by erosion . ... Publications with keywords: Earth - Richat Structure . Publications with words: Earth - Richat Structure . ...