Everything Everywhere Daily: History, Science, Geography & More - The Sahara Desert Wasn’t Always (Encore)

Starting point is 00:00:00 Hey everyone, this is Gary. I'm off this week visiting the beautiful Commonwealth of Puerto Rico, where hopefully I will not be stranded due to a hurricane. I've hand-selected some of my favorite episodes for you to enjoy this week, which statistically speaking, I know most of you haven't listened to yet. I will be back again next week, fully rested with fresh new episodes for you to enjoy. The Sahara Desert is by far the largest desert in the world. It evokes images of sand dunes, camels, and just being really dry. However, it didn't always used to be that way. Quite recently, geologically speaking, it was a place with grasslands and forests. While it disappeared and became a desert, some think a green Sahara might return in the future. Learn more about how the Sahara Desert

Starting point is 00:00:42 wasn't always a desert on this episode of Everything Everywhere Daily. What if your perceptions about the past were wrong? ThruLine is a podcast that takes you back in time to uncover the parts of the story that may have gone unnoticed. It effectively turned day and tonight. And how it shaped the world now. Time travel with us every week on the ThruLine podcast from NPR. It might seem hard to believe, but the area we call the Sahara Desert once was a lush green place where humans and animals lived and thrived. This wasn't something that occurred millions of years ago, or hundreds of thousands of years ago, or even 10,000 years ago. Researchers have determined that the Sahara might have only become a desert 5,500 years ago. And that seems like a long time, but it really

Starting point is 00:01:46 isn't that long at all geologically. I'll start with a quick overview. The Sahara Desert is the largest non-polar desert in the world. Technically, Antarctica is a desert, and it's larger than the Sahara, but it doesn't really evoke images of what we think of as a desert. The Sahara basically makes up the entire northern quarter of the continent of Africa, save for the fertile areas around the coast and the Nile River Basin. It has a total area of 9,200,000 square kilometers, or 3,600,000 square miles, and that is approximately the same size as the United States or China. Most of it lies within the countries of Algeria, Libya, and Egypt. The countries immediately to the south, Mauritania, Mali, Niger, Chad, and Sudan, also have significant parts of their

Starting point is 00:02:28 countries in the Sahara, but are mostly in the semi-arid Sahel region, which I'll discuss in a future episode. The region consists mainly of rocky outcrops and sand dunes, some of which can reach 180 meters or 590 feet high. And of course, some of the hottest temperatures ever recorded on Earth have occurred in the Sahara Desert. There are people who live in the Sahara, but not that many. There is a total population of only 2.5 million inhabitants over the entire Sahara region across all countries, or roughly one person per square mile, which is less than the population density of Alaska. So how do we know that the Sahara used to not be a desert? The evidence is all around if you just look hard enough. For starters, there's cave art located in many places in the Sahara which

Starting point is 00:03:12 show animals which don't live in the Sahara today. It isn't just a few instances of rock art either. It's dozens of them with thousands of paintings and carvings. The animals depicted include buffalo, elephants, rhinoceros, orrochs, horse-type creatures, giraffes, antelopes, and hippopotamus. It's incredibly implausible that so many people would travel so far across such an inhospitable terrain just to paint images of animals which don't exist where they were. However, there's a lot more evidence than just rock art. Archaeological digs, dried lake beds, animal fossils, trap pollen, radioisotope analysis, and plain old geologic stratigraphy all point in the same direction. The Sahara wasn't a desert just over 5,000 years ago. In the country of Niger in 2005 and 2006,

Starting point is 00:03:56 over 200 graves were found on the shore of an ancient lake. Two of the bodies were buried on a bed of flowers, which don't exist in the desert. Along with the graves, they also found the remains of animals, including large fish and crocodiles, which definitely do not live in the Sahara. They were members of a group called the Kiffians. Another method of determining what the Sahara was like in the past is to analyze the dust and sand which blows off the desert. There's a regular amount of dust which blows from the Sahara into the Atlantic Ocean. Ocean sediment analysis has given us a history going back several hundred thousands of years. It was also actually written about in antiquity. The Greek historians Herodotus and Strabo

Starting point is 00:04:34 centuries apart from each other, offhandedly mentioned that the Sahara was once green. So, what was the Sahara like back then? Basically, think what it's like in the Serengeti today. It would have been a grassland with tons of grazing animals as well as associated predators. This would have been an area far larger than the Asian steppe, the North American Great Plains, or the South American Pompas. In fact, it would have been bigger than all of them combined. This enormous grassland would have drawn human beings as it would have been a fantastic. area for hunting. From the graveyard found in Niger and numerous rock art drawings found all throughout

Starting point is 00:05:09 the region, that is exactly what appears to have happened. It also means that there is probably a lot of evidence of human habitation, which hasn't been found, because it's lying deep beneath some sand dunes. And it also puts a different twist on the rise of civilization in the region. When the rains dried up and the desert began encroaching on the grasslands, most of the people who live there would have had to have left. That would have meant migraining either to what is now the Sahel in the south, the Atlantic coast in the west, the Mediterranean coast in the north, or the Nile River Basin in the east. I don't think it's a coincidence at the end of the Green Sahara period coincided with the rise of dynastic Egypt. Hunters and pastoralists from the Green Sahara may have wound up migrating east and becoming farmers in the Nile basin.

Starting point is 00:05:51 It's entirely possible that these migrants from the Sahara could have come in conflict with people in the regions where they migrated to, and those conflicts were just never recorded. All of this is actually pretty fascinating, but it really just raises the bigger question, of what exactly happened. How did one of the largest lush and verdant places on the planet become one of the largest deserts on Earth? To understand this, we need to understand climate science. The Green Sahara period is technically known as the African humid period, or to get more technical, periods. One of the things they've discovered from ocean floor sediment is that the Sahara actually goes in cycles of about 20,000 years. It seems to go from the desert

Starting point is 00:06:30 to green and back to desert again over and over. The reason for this appears to have to do with Milankovych cycles. I previously did an entire episode on Milankovych cycles, and for a quick refresher, they are the long-term climatic cycles that the Earth goes through based on the procession cycles of the Earth around the Sun, as well as the change of the tilt of the Earth. In this case, it's primarily the change in the tilt of the axis of the Earth that matters. 8,000 years ago, the axis of the Earth was tilted at about 24.1 degrees, and today it's 23.5 degrees. That doesn't sound like much, but it actually had a huge impact. Also, the direction of

Starting point is 00:07:08 the tilt has changed. Today, the earth is closer to the sun during the northern hemisphere winter and the southern hemisphere summer. When the Sahara was green, it was the other way around. That meant during the African humid period, there was more solar radiation during the summer. You might think that more radiation in the summer would increase desertification, but in the case of the Sahara, it meant more evaporation and an increase in monsoon rains. In other words, when more solar radiation falls on the northern hemisphere in the summer, it can change wind and rain patterns such that it brings rains to the area that we call the Sahara. So, okay, the earth goes through the cycles which can change weather patterns.

Starting point is 00:07:47 But why did everything change so fast? The reason why this most recent change may have occurred so rapidly could have had to do with humans. If the humans who lived there were pastoralists and they had animals like goats or sheep, they may have accelerated the removal of grass through over grazing. As I mentioned before, 5,500 years ago is not that long ago in terms of geology. For the creation of a desert, however, it's quite fast, but this is well within the time period where early civilization and cities existed. The creation of the Sahara Desert resulted in radical changes, which affected civilizations

Starting point is 00:08:19 in West Africa, the Horn of Africa, Egypt, and the Mediterranean. In fact, some of those civilizations might owe their existence to the Sahara. The creation of the Sahara Desert put a gigantic natural barrier that separated the continent. It impacted trade as well as the migration of animals. In fact, to this day, it's common to think of Africa as sub-Saharan Africa and North Africa. I'll close by noting that it's very likely someday in the future, thousands of years from now, that the Sahara will once again bloom. The Earth will change its tilt, the Earth's orbit will process, and animals will graze on what are today sand dunes. The executive producer of Everything Everywhere Daily is Charles Daniel.

Starting point is 00:09:04 The associate producers are Thor Thompson and Peter Bennett. I just want to thank everyone, including the show's producers, who support the show over on Patreon. If you'd like to support the show, just head over to patreon.com, which is currently the only place where you can get show merchandise. Also, if you want to talk to other listeners about the show, head over to our Facebook group or Discord server, both of which have links in the show notes.

Everything Everywhere Daily: History, Science, Geography & More - The Sahara Desert Wasn’t Always (Encore)

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