In the midst of the vast, vacant Sahara desert, just outside of Ouadane, Mauritania, lies a 30-mile wide geological oddity known the Richat Structure, sometimes called the “Eye of Africa.” From space, this natural curiosity forms a distinct and unmistakable bull’s-eye that once served as a geographical landmark for early astronauts as they passed over the Sahara.

Once thought to be an impact crater due to its circularity, the unusual formation is now widely believed to have been caused by the erosion of a geological dome formed by pressure from a bulb of molten magma below. The desert floor ‘blistered,’ and as the layers of rock were pushed up and fractured, millennia of weathering gradually leveled them flat again, exposing the structure’s distinctive concentric rings.