It has happened in the past and it will happen again in the future. The Sahara, a desert almost as large as the contiguous United States of America; so harsh the name literally means The Great Desert. But the array of life here will surprise you. Bears live and hunt in the high Atlas Mountains. Crocodiles have been found grasping onto survival amongst water holes in Southern Mauritania. The same species of fish have been found in oases thousands of miles apart and separated by nothing but sand, wind, and rock. But for all the world the desert should be an impassable wasteland. These animals should not be here.
The truth is that the desert was not always so inhospitable. In fact, during its infrequent wet periods the Sahara would seem much different. The latest wet period was known as the Neolithic Subpluvial and lasted from about 7000 BC to about 3900 BC. During this time the Sahara would have appeared as vast savannah grasslands, much like current subsaharan Africa. With no desert to bar movement, animals would be able to freely travel between the Middle East, Southern Europe, and Africa. Even fish were able to spread (somewhat) unhindered. Humans were no exception, and it is actually thought that this cycle may have contributed to our exodus from Africa. More than once in our history our ancestors may have followed a series of large lakes northward out from the Olduvai area, dating as far back as the days of Homo erectus. Skeletons and other remains have been unearthed throughout the Sahara and more modern human movements have even left behind exquisite rock art depicting hippos, giraffes, and swimming figures.
It has even been suggested that the last sudden drying of the Sahara (known as the 5.9 kiloyear event) may have rocked our ancestors so that entirely new ways of thought arose. In Steve Taylor’s book, “The Fall”, he suggests that this triggered, “the rise of patriarchy, institutionalised warfare, social stratification, abuse of children, the development of the human ego, separation from the body, the rise of anthropomorphic gods and the concept of linear historic time.”
The reasons for the Sahara’s variability are complex. In part the cycle of glaciation and warm periods determines the amount of rain. Ice ages tend to be drier, with less rainfall and reduced ocean levels. The cycle can also be affected by the orbit and tilt of the Earth. Earth wobbles like a top as it circles the sun, and it’s path is not always identical in shape. The different alignments can deprive or glut an area with sunlight, changing global weather systems. Interestingly enough, this cycle means that the Sahara will turn green again sometime in our future. Climate change may even bring that about within the next millennium, although this remains to be seen.
For more stunning pictures of archaeological digs I highly recommend this Boston article.