During present day there is a small lake in Chad called Lake Chad. Much evidence from many different sources has been laid out to strongly support the existence of a much larger Lake Mega-Chad during the nearest thousands of years before today. The size of the lake would have been larger than any of the largest lakes in the world today. It is quite clear that such a lake existed 5 to 10 thousand years ago (source?!?!).
In this article I shall lay out the evidence in support of extending the existence of Paleolake Mega-Chad millions of years into the past. In fact I shall suggest that it existed not only during the Quaternary (the last 2 million years) but even during the entire Neogene period (the last 23 million years)!
Concrete evidence
At the time of writing this post, the oldest found human ancestor fossil was found in that area. [source]
The soil layer it was found in was 7 million years old. The sediments there, and in the immediate surroundings, clearly indicate it was a marshland, lake shore or swamp. The findings of plenty of seeds indicate that large trees were nearby. [source: Megalake Chad impact on climate and vegetation during the late Pliocene and the mid-Holocene]
100 million years ago
100 million years ago the area of Lake Mega-Chad was still the location of a very shallow ocean. The area was busy being pushed up to higher altitudes thanks to the neighbouring plates pressing towards eachother. So come about 40 million years ago it had risen high enough to isolate the basin from the rest of the ocean, forming an inland sea. This much is known from the movement of tectonic plates [source…?].
This inland sea was close to the equator and very shallow, as a result it was quite warm and had rapid evaporation. We can use the locations of the landmasses to coarsely sketch out the approximate climate of that period, like in this image: (produce image)
The image was produced using …..
The humid air was transported to the areas around the basin, rising up …. causing much rainfall across the entire north african continent. As the (now endorheic) basin now held an inland sea, it became brackish and, like all other endorheic lakes it had periodic flooding events.