The Sahara Desert, spanning 9 million square kilometers across 11 countries, was once a lush and green area thousands of years ago. However, it transformed into a harsh arid region due to changes in the Earth's orbital axis and possibly overgrazing by nomadic humans and their animals.
The desert holds many secrets and discoveries, including the remains of whales that once roamed the area when it was a tropical sea. Fossils of these whales, some 50 feet long, have been found in the Egyptian desert, providing clues to the evolution of whales.
The "Eye of the Sahara," a geological formation in Mauritania, was initially believed to be an impact crater but is now thought to be a geologic dome containing rocks over 100 million years old. Some speculate that it could be the remains of the lost city of Atlantis, described by Plato as a circular city with mountains to the north and rivers flowing around it.
Other mysteries of the Sahara Desert include the "Clayton Rings," conical pottery cylinders found in the Egyptian desert, which were likely used by nomadic herders but whose exact functions remain unknown.
Here are the key facts extracted from the text:
1. The Sahara Desert covers 9 million square kilometers.
2. The Sahara Desert spans across 11 countries: Algeria, Chad, Egypt, Libya, Mali, Mauritania, Morocco, Niger, Western Sahara, Sudan, and Tunisia.
3. The Sahara Desert is bordered by the Atlantic Ocean to the west, the Red Sea to the east, the Mediterranean Sea to the north, and the Sahel savannah to the south.
4. The Sahara Desert is home to sand dune fields, mountains, plateaus, and gravel-covered plains.
5. The Sahara Desert was once a tropical area, but it became a harsh, arid region due to changes in the Earth's orbit and overgrazing by humans and their animals.
6. The Sahara Desert has been subject to periodic bouts of humidity and aridity throughout Earth's history.
7. The transition from humid to dry conditions in the Sahara Desert occurred rapidly between 8,000 and 4,500 years ago.
8. Archaeologist David Wright found a pattern of pastoralists and their domesticated animals in the Sahara Desert, which corresponded to changes in plant types and varieties.
9. The presence of humans and their animals in the Sahara Desert may have triggered the end of the humid period more abruptly than can be explained by orbital changes.
10. The Sahara Desert was once home to whales, as evidenced by fossils found in the Wadi Al-Hitan in Egypt.
11. The fossils of whales in the Sahara Desert date back 37 million years to an era when a shallow tropical sea covered the area.
12. The whales that once lived in the Sahara Desert were likely terrestrial mammals that eased into the ocean over millions of years, gradually losing their four legs.
13. The Eye of the Sahara, also known as the Richat Structure, is a geological formation in the Sahara Desert that resembles an enormous bullseye.
14. The Eye of the Sahara stretches across a 40-kilometer-wide region of the desert in Mauritania.
15. The Eye of the Sahara was first photographed in the 1960s by Gemini astronauts and was later studied by geologists.
16. Geologists initially believed that the Eye of the Sahara was an impact crater, but lengthy studies of the rocks inside the structure show that its origins are entirely earth-based.
17. The Eye of the Sahara is a geologic dome that contains rocks at least 100 million years old.
18. Some rocks in the Eye of the Sahara date back to well before the appearance of life on Earth.
19. The Eye of the Sahara includes igneous, volcanic deposits, and sedimentary layers that form as the wind pushes dust and water deposits.
20. The Clayton Ring is a conical pottery cylinder open at both ends, found in the Sahara Desert in Egypt.
21. The Clayton Ring was not used by Egyptians living along the Nile, but rather by nomadic herders inhabiting the Dakhla Oasis during Egypt's first dynasties.
22. The Clayton Ring has been found in the oasis around seasonal hunting and herding camps, as well as up to 300 kilometers away from permanent water sources.