Final answer:
The Sahara Desert became increasingly arid around 6000 to 2500 BCE due to climatic shifts and human activities such as overgrazing. This led to a drastic transformation from a lush environment to the expansive, arid desert we see today.
Step-by-step explanation:
The Sahara Desert underwent a significant climatic shift and became increasingly arid around 6000 to 2500 BCE. This was a period following the last Ice Age when the Sahara Desert transitioned from a lush region with monsoon-like weather to a vast arid desert. The desertification process was enhanced by changing climate conditions and human activities such as overgrazing, which led to the retreat of the rainforest and expansion of desert zones. This brought about changes in the way people lived, from pastoralists who hunted and gathered to adapting to the harsh desert conditions. The Sahara is now the largest hot desert in the world, covering much of North Africa, and it continues to grow and impact the surrounding regions, including the Sahel, as it shifts southward.