When The Sahara Wasn’t a Desert

A series of scientific discoveries tell us a story that not everybody knows about the Sahara Desert

We love story time. Every night, before bed, we read to our kiddos. Sometimes, we choose modern stories with colorful pages, and other times, we go back to the classics.

The other night, I was reading my almost-four-year-old The Little Prince. If you haven’t read it, the story occurs after a pilot crashes in the Sahara desert. My curious son knows about the existence of deserts, but we haven’t had the opportunity to talk about what such a big and arid landscape implies for human survival.

Of course, questions started falling, and I soon had to close the book and think about everything desert-related: Mom, was the Sahara always a desert?

Oh, kiddo, that’s a good one! I think I need to write a story about it…

Imagine the Sahara Desert today — a vast, arid landscape filled with sand dunes and almost no water in sight. It’s hard to picture it as anything else, right? However, this unique landscape was a completely different place thousands of years ago.

What if I told you that the Sahara was once a lush, green region teeming with life? So, of course, you’d have a lot of questions, right? How did this dramatic transformation happen? How do we know it wasn’t always a desert?

The Sahara’s greening periods, known as the African Humid Periods (AHPs), were driven by changes in Earth’s orbit. These periods occurred about every 20,000 years due to a phenomenon called precession — a wobble in Earth’s axis that alters the distribution of sunlight. See the video below if you’re curious about it. The author explains it way better than I ever could with just words!

But let’s go back to the Sahara. About 11,000 to 5,000 years ago, one of these AHPs transformed the Sahara into a verdant landscape. The increase in summer solar radiation during this time (due to precession) warmed up the land, strengthening the African monsoon. This brought more rain to the region, causing the Sahara to bloom with vegetation, rivers, and lakes.

But how do we know this is actually true? Evidence of these green periods is all around us. However, some of the most fascinating proof comes from ancient rock art found across the Sahara.

When ancient artists painted scenes of their surroundings, they didn’t depict a desert. Instead, they painted hippos, giraffes, elephants, and even people hunting or herding cattle. That’s not what a desert looks like at all; that’s characteristic of a savannah ecosystem. So, these images tell us that the Sahara was once home to a variety of water-dependent animals and human communities who thrived in the region.

However, beyond rock art, scientists have uncovered various geological and climatic evidence pointing to a greener Sahara. One key piece of evidence comes from deep-sea sediment cores off the coast of Mauritania.

These cores show changes in the amount of dust blown off the Sahara over time. During the African Humid Periods, these sediment cores show that there was significantly less dust, suggesting that the region was wetter and had more vegetation. Pollen grains found in these sediments support this, showing an increase in plants like grasses and a decrease in desert species.

So yes, all evidence points to a greener Sahra not that long ago — at least from a Paleontologist perspective, who’s used to thinking in millions of years.

But the Sahara’s transformation wasn’t just about the presence of greenery and charismatic big animals. During these humid periods, the region also featured large bodies of water.

Indeed, geologists have discovered ancient lake beds and river systems across the Sahara. Some of these lakes were enormous, like one that was bigger than all the Great Lakes combined. This network of lakes and rivers allowed animals and humans to thrive and move through the region.

Archaeologists have found evidence of vibrant communities around these waterways, including tools, pottery, and remnants of ancient settlements. These are definitely thriving communities!

However, this lush environment didn’t last forever. Around 5,000 years ago, the African Humid Period came to an end. Earth’s orbit shifted again, reducing the amount of solar energy hitting the Northern Hemisphere and weakening the monsoon, the climatic event that brought it so much rainfall.

As a result, the rains moved south, and the Sahara began to dry up. The dust records show a sharp increase in aridity (see previous chart), and the rock art began to show animals more suited to a desert environment. Human populations were forced to move, many clustering around reliable water sources like the Nile River.

But this is not the whole story. What’s even more fascinating is that the Sahara has been greening and drying repeatedly over millions of years.

The African Humid Periods are the latest in a long history of wet and dry cycles, with over 230 green periods identified in the last 8 million years. These cycles are a natural part of Earth’s climate system, influenced by the planet’s orbit and other factors like ice sheet extent and atmospheric changes. As you see, everything is interconnected.

So, what does all this mean? For one, it shows us how dynamic and ever-changing our planet is. The Sahara wasn’t always a desert, and it may not always be one in the future (although we are talking about thousands of years, so don’t book your flights yet).

These past transformations highlight the delicate balance of Earth’s climate systems and how even slight changes can dramatically impact the environment and its creatures. May they remind us of how delicate our climate is, just like the Little Prince’s planet.