Secrets of Sahara Desert

The word Sahara usually brings to mind a picture of endless sandy landscapes, a caravan of camels is walking along the dunes, the sun is beaming brightly as if for the last time and around you not a soul.  It seems as if the golden majestic dunes have always been here but this isn't so, what secrets does the great desert hide from humanity and what is under its hot sands.  This is hard to believe but as recently as 6000 years ago the arid desert with an area of more than 9 million square kilometers almost 3-1/2 million square miles was covered with a thick green carpet, entire settlements existed and domestic animals grazed, where today there's practically nothing but hot sand there were green Meadows and lakes, rainfall was so abundant that it fed the river Tamanrasset carrying its waters across the green Sahara to the Atlantic Ocean, the river with numerous tributaries, had a link approximately 500 kilometers or 311 miles and would have made the list of the longest rivers in the world.  In 2015, 3-dimensional satellite images helped to find the largest Palaeo river, thanks to these images.  Scientists noticed the smooth edges of the ancient channels of the river hidden under the modern day desert and in Central Africa, there was a lake called Lake Mega Chad now merely a ghost Lake of which only the modern Lake Chad remains and once in antiquity this lake was wider than the Caspian Sea extending to almost 390,000 square kilometers or 150,000 square miles across the Sahara.  If the lake existed now it would be the largest on the planet.  The images published by NASA clearly show how huge it was the Lake forever imprinted in a desert landscape like a silent reminder to all of humanity who had a hand in draining the once deep water reservoir, but what happened, why did this once green and prosperous region suddenly become the most lifeless place on the planet.  Scientists have different explanations for example environmental archaeologist David Wright considers livestock to be the main cause of climate change for a third of the African continent.  Sheep, cows, and goats trampled and consumed local vegetation.  The soil became more exposed and reflected more sunlight affecting the atmosphere, the amount of precipitation decreased and drought began, that was the beginning of the end, drought slowly but surely destroyed all the vegetation and the green Sahara turned into a huge desert region about the size of the United States, but this doesn't mean that only animals are to blame, perhaps cattle farmers were the catalyst for a process they had already begun to destroy the green cover, true not everything is so simple.  In 2018, another team of scientists put forward the hypothesis that the ancient herders on the contrary prolonged the flowering of the green Sahara by another 500 years.  According to one of the authors of the study seasonal cattle driving and selective grazing helped people maintain a declining ecosystem.  A third group of scientists blames the earth's axis, having studied the dust precipitating off the coast of West Africa for the last 240,000 years, they've come to the conclusion that the climate of the Sahara and North Africa changes from humid to dry every 20,000 years as the tilt of earth's axis changes, it shift affects the distribution of sunlight between seasons, the more solar radiation, the more active the monsoon and the more precipitation falls during the summer.  When there's less sunlight, the monsoons weaken and a moist climate turns into drought.  If this is so, then after some 10,000 years Meadows will again bloom in the Sahara and animals will graze, but the invisible river and the ghost lake are far from being the only mysteries that the majestic desert hides from us.  Earlier in the Mesozoic era, the Tethys Ocean seethed here dividing the ancient continent of Gondwana and Laurasia, the ocean receded, the continents were divided, the plates moved and on the surface of the sand it seemed a cemetery of whales remained, this place is now called Wadi El Hitan, which in Arabic means the Valley of the whales.  You probably will be surprised but modern whales have ancient ancestors, Basilosaurus had sharp teeth and hind limbs, true their limbs were very small and not suitable for movement, they were probably the largest predators of their time because the size of the Basilosaurus reached 21 meters or 69 feet, imagine how scientists were shocked when in the early 20th century they found the remains of ancient whales in the hot desert along with fossils of extinct prehistoric fish, snakes, turtles, crocodiles, and manatees probably their first thought was someone must have brought them here but everything turned out to be much more interesting, the sands of the Sahara keep other secrets.  Not only did ancient predatory whales hunt there but once upon a time dinosaurs also roamed, one of the largest dinosaurs in the world who's age is almost a 100 million years old was found here.  These were the bones of a herbivorous Sauropods which was called Paralititan Stromeri, judging by the fossils, this giant could reach 32 meters or 105 feet in length and weigh up to 60 tons and in 2018 under the vast desert sands the bones of another previously unknown dinosaur were found, Mansourasaurus, the discovery was like an exploding bomb.  There was very little data on the last days of the dinosaurs that lived in Africa in the late Cretaceous 100 to 66 million years ago, also it turned out that the new species of dinosaur is very similar to its European counterpart, so it seems the dinosaur came to Africa from the territory of modern Europe but how is this possible.  Previously scientists were convinced that the ancient giants could not move between continents after they became separated, but this unexpected find smashed the accepted theories of dinosaur migration.  The newly discovered species could reach from 8 to 10 meters or 26 to 33 feet in length and weigh as much as an African bull elephant up to 6-1/2 tons.  Today this find is considered one of the most significant among all discovered remains of new dinosaur species and the amazing discovery of the Mansourasaurus can give us much more information about the fauna of that period, but perhaps the most inexplicable mirror of Sahara in Africa and one of the major mysteries of the planet is located in Mauritania, it's a unique geological formation easily visible from space called the Eye of the Sahara or Rechat Structure, it's a series of huge concentric rings and has a diameter of about 50 kilometers or 31 miles.  The object gained world fame after it was discovered in 1965 from the man spacecraft Gemini IV.  Since then, the mysterious eye haunts scientists, all these years they've been looking for the answer to the main question what is the nature of this structure, if this is the site of the fall of an ancient meteorite then where's the crater itself and why are no traces of the impact detected; if this is the mouth of an extinct volcano that was collapsing inwards for millions of years then why are volcanic rocks completely absent, very fantastic theories are also being put forward about an alien landing site or the location of Atlantis here, but most of all scientists are inclined to believe that the structure formed as a result of erosion, but there is a flaw in this hypothesis the formation ring is too even and regular nowhere else on earth has erosion been able to create anything like this.  Anyway the mysterious eye of the Sahara remains one of the most amazing natural phenomena, so whom or what the desert is watching with the help of this eye, most likely this will remain a secret.  The desert is also silent about the cities and entire civilizations buried under its sands, traces of which are recorded by satellites and sometimes discovered by archaeologists.  Once upon a time, life was vibrant here, fortresses stood, fields were waiting to be harvested and livestock grazed on pastures.  Here wild animals roamed in search of prey and fish splashed in the rivers but everything is changed, now the desert is completely inhospitable, everyone who tries to explore the vast expanses of the Sahara deals the strength of the sizzling sun and sand storms who knows perhaps under the hot dooms the biggest secret of the Sahara is still waiting which it carefully protects from human eyes.