Review of WHEN THE SHARA WAS GREEN
The geological history of the earth’s greatest desert
The Sahara Desert is massive. It extends nearly 3,000 miles (5,000 kilometers) from west to east. It’s one of the driest places on earth. About its covered with iconic sand dunes.
But it hasn’t always been this way.
Most familiar with geology will suspect this. Our landscapes – which seem stationary in the brief blip of time we get on this earth – are ever changing. Billions of years of earth’s history are etched in the rocks and landscapes we traverse. The Sahara is no exception.
When the Sahara Was Green: How Our Greatest Desert Came to Be by Martin Williams details the geological history of the great desert and specifically how the once green landscape became the dune covered desert the world knows today.
It was not until about seven million years ago (a geological blip, really) that the Sahara began its arid decent from a landscape once covered by crisscrossing rivers and savanna woodland. Two primary factors contributed to this change: the northward progression of the African continent to its current location (and the consequent closing of the great Tethys Sea, of which the Mediterranean Sea is what is left), combined with the enormity of the desert which doesn’t allow for moisture to penetrate the middle of the desert.
During this period, however, there were relatively wetter periods during which humans and other large animals lived on the land. Most recently, between 15,000 and 5,000 years ago, there were large areas of savanna woodland and grassland, fed by large rivers that flowed, and home to animals such as hippos.
The most interesting fun fact I learned from this book though was where all the sand comes from. Have you ever thought about it? I had not. It’s just there. In an ironic twist, the desert sand (which covers only about one fifth of the Sahara, actually) comes from rivers. Yes, the greatest desert in the world gets its iconic look from water. In the Sahara there are highlands and mountains, which do get moisture. And, recall, the Sahara was once covered with rivers. As water and floods flow through these channels, sand and sediment are created, depositing large amounts of what is now the stereotype of the Sahara.
Overall, When the Sahara Was Green is a highly accessible book, relatively brief, and filled with interesting facts about geological history. The end section and epilogue took a sharp political turn after a highly apolitical book, but such is expected in nearly any earth science book given the easy connections to climate change.
Published: October 2021
Format: Hardcover
If you think this sounds interesting, bookmark these other great reads:
How the Mountains Grew: A New Geological History of North America by John Dvorak (2021)
Jungle: How Tropical Forests Shaped the World by Patrick Roberts (2021)
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