Deep in the Sahara, in the Mauritanian desert, lies a remarkable phenomenon. Known to western geologists at least since the 1930s when French geographers first put it on the map, the Richat Crater or Richat Structure has been the subject of much speculation by scientists.
In 1965, astronauts Ed White and James McDivitt were on the Gemini IV space mission (when they completed the first US space walk) and took a photograph that fanned the flames of the Richat Structure debate.
Since then the Richat Structure has been dubbed 'The Eye of the Sahara' and with such perfect concentric shapes as seen from above, many questioned whether it could have been made by natural forces.
What is the Richat Structure?
Located in the Mauritanian desert, on the Adrar Plateau of the Sahara desert, the Richat Structure is a mound of rock exposed in concentric circles. There have been many debates about what could have caused the Richat Structure, ranging from molten rock from below, to extra-terrestrial rock from above.
In the Mauritanian desert, near the Richat Structure, three significant impact craters – Aouelloul, Temimichat-Ghallaman and Tenoumer – were discovered in 1952 by naturalist Théodore Monod. So although in 1948 geographer Jacques Richard-Molard speculated it had been created from magma rising through the Earth's crust, after the other impact craters were discovered, it was believed that the Richat Structure was the same.
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In fact, in 1969 American geologist Robert Fudali demonstrated that it couldn't be an impact crater like the other three. The Richat Structure hadn't been hit by a meteor at all, and a paper published in the journal Geology by Guillaume Matton, Michel Jébrak and James Lee in 2005 determined that it is an eroded geologic dome, formed when molten rock pushed up from beneath.
Originally a dome, it was subject to erosion over many, many years by sand and wind which transformed the dome into the circular ridges that you can see from space. The oldest rocks are at the middle, the youngest at the edges.
How big is the Richat Structure?
The Richat Structure has a diameter that measures 40km (around 25 miles), big enough so that if you were standing on the ground, you wouldn't have any idea you were standing inside a circle. Its age is debated and hard to discern, but it does predate humans by tens of millions of years.
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What have they found in the Richat Structure?
In short: a lot. A large amount of interesting artifacts have been found at the site, including Acheulean stone tools and other evidence of early humans (Homo erectus and Homo heidelbergensis) who lived and hunted nearby. Most of the tools found come from the ring right on the outside of the structure and there have also been Neolithic spears found at the site.
Researchers have also found evidence of stone artefacts made by modern humans from the middle to late Pleistocene period, along with stone burial mounds which have yet to be excavated. What they haven't found at the site is the lost city of Atlantis, as described by Greek philosopher Plato. Many people speculate that the Richat Structure could have been the home of the utopian society he wrote about in his dialogues around 360 BCE. This theory, however, is easily discredited if you talk to geologists, who point to just how old the structure is.
Wildlife in the Richat Structure
Studies of the Richat Structure have mainly been geological, but it is situated in the Mauritanian desert – which makes up 90 per cent of Mauritania – within the Sahara desert. The vast expanse is home to a wide variety of animals from wild dogs and camels, to birds, reptiles and other animals like ants, scorpions and jerboas.
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Top image: Richat Structure in Western Mauritania, with colour and other elements of this image added by NASA. Credit: Elen11 via Getty
