The Sahara Desert might appear to be an unlikely place to be looking for evidence of an ice age. It’s one of the hottest and driest locations on the planet; a desolate wasteland which covers an area larger than Australia and which is estimated to be at least 2.5 million years old. However, in the past thirty years, Saharan researchers have unearthed amazing proof that conditions were once markedly different.
Archaeological evidence, including bones, fossils and cave paintings, indicates that the Sahara was once home to mighty beasts such as elephants, hippos and buffalo, as well as to thriving Neolithic cultures. Not only that, but a wealth of geological data confirms that in the distant past–150 million years or more–the Sahara was covered by an ancient sea, complete with fish and large reptiles. Even today, buried deep beneath the sand are channels that were once broad riverbeds, and a massive subterranean sea which may encompass as much as 150,000 cubic miles of fossil freshwater.
It is theorised that these astonishing transformations were caused by radical climate shifts. For instance, around 8000-10,000 years ago, the last ice age–or the current one, depending on definitions–reached the end of its peak, and northern banks of ice began to melt. This brought monsoonal rains which filled lakes and valleys and which led to forests growing in some mountainous regions.
Archaeologists have uncovered bones and tools from this period which provide evidence of widespread hunting, and rock art from several locations–including more than 15,000 images from Tassili n’Ajjer alone-depicts wildlife, vegetation and indications of a complex human culture. It seems, however, that this fertile period ended about 4,500 years ago, and the Sahara reverted to the desert conditions that exist today.
What, then, of more ancient ice ages? Again, the Sahara’s distant past is offering up clues to researchers about dramatic and far reaching climate changes. Although there is still considerable debate about what causes an ice age, that they have, in fact, occurred is supported by three major types of evidence.
The first of these is geological evidence based on glaciation, such as rock scouring, glacial moraines and drumlins. The second is chemical evidence, such as ice core samples, and the presence of certain isotopes in fossils found in sedimentary rock. And the third, and most significant as far as the Sahara is concerned, is paleontological evidence. The relatively undisturbed fossil records of the Sahara region tell a remarkable tale. What is now a desert was once occupied by sea-going ammonites and fish, by large and fearsome dinosaurs and by mammals such as giraffes and gazelles.
By themselves, none of these types of evidence offers certainty about the climate of the distant past, but when combined they paint a compelling picture. Scientists now believe that there have been at least four major ice ages, the first of which–the Huronian-may have occurred more than 2.3 billion years ago. The second, and most severe, of the ice ages occurred between 850 and 630 million years ago, and may have caused a "Snowball Earth" effect, which encased the whole planet in ice.
From 460-430 million years ago, there was a third, relatively minor, event known as the Andean-Saharan ice age, and the fourth, which may still be underway, apparently began about 2.5 million years ago. According to the experts in such things, the Earth is currently in an "interglacial," or warmer period, which is known as the Holocene. What is commonly thought of as an ice age–the world of Sid, Manny, and Diego-is simply one of the many glacial periods that occur during any given ice age.
Although there are many mysteries still to be revealed about the causes and effects of ice ages, researchers are gradually discovering new information that may one day lead to an almost-complete understanding of them. And, as unlikely as it may first appear, one of the places they will be doing that is in the sands of the Sahara.