The Sahara desert was not always a desert. It was once a green oasis with lakes, rivers, grasslands, and even forests... Here some theorys about what happens to change the Sahara :
One theory says that the monsoon in Northern Africa was weakened because of glaciation during the Quaternary period, starting two or three million years ago. Another theory is that the monsoon was weakened when the ancient Tethys Sea dried up during the Tortonian period around 7 million years ago.
Orbital precession : The transition from humid to dry happened far more rapidly in some areas than could be explained by the orbital precession alone, resulting in the Sahara Desert as we know it today
Climate change: Human-caused greenhouse gas emissions have led to runaway climate change, which has caused the Sahara to become a desert. However, the Sahara could turn green again due to the Earth's constantly changing orbital rotation around its axis, a pattern that repeats itself every 23,000 years
Shifts in the world's weather patterns**: As little as 6,000 years ago, the vast Sahara Desert was covered in grassland that received plenty of rainfall, but shifts in the world's weather patterns abruptly transformed the vegetated region into some of the driest land on Earth
Desertification**: Desertification is an increasingly widespread problem as climate change modifies weather patterns, leaving people to deal with hyperarid conditions. The Sahara Desert is no exception, steadily growing across 11 countries and soon to cover more
In summary, the Sahara turned into a desert due to a combination of natural factors such as weakened monsoons, orbital precession, and shifts in the world's weather patterns, as well as human-caused climate change and desertification.
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