re: #103 iceweasel

Yes. Tell us a story, please.

A long time ago (5500 years) on a continent far, far way (Africa), the world changed for the plants, animals, and people who lived in that land. For 9000 years they had lived in an area with good monsoonal rains, that made the land green and allowed the animals and humans to flourish.

But that land turned into the largest stretch of desert - the Sahara, and the people and the animals were not happy campers.

That period of time (in that land) is called the African Humid Period (AHP). The wiki link takes to you a discussion of a large lake left over from that period, and introduced you to the controversy over how quickly the AHP ended.

The research presented this week (erroneously stated by myself as happening last week) confirms the idea that the termination of this period happened quickly (in geological terms), probably within 1 to 2 centuries. The research was taking core samples off the African west coast (through a range of latitudes) and analyzing the dust sediments.

The summary (see pg 21):

Our preliminary results on the N-S sediment core transect indicate that an abrupt termination of the AHP near 5.5 ka BP can be traced from Senegal to the Canary Islands (roughly 18-28N). Most cores have sedimentation rates that were considerably lower than at Site 658, and thus have lower resolution, but the AHP transitions were always more rapid than expected from linear orbital monsoon forcing alone. Surprisingly, we find that the end of the AHP occurred nearly synchronously for all cores along this transect, suggesting a very rapid and spatially extensive retreat of the African monsoonal rains near 5.5 ka BP.

More information than you might be interested in, but…. better too much than too little.

I became interested in this as not long ago I was reading up on how the civilization in ancient Egypt started, got drawn to a discussion of evidence of early human civilization (pre Pharaoh) in SW Egypt, which led naturally enough to discussions about the AHP.

In the big picture, the hypothesis would look like this:

rapid climate change ➠ humans migrating from pasteur lands to the Nile ➠ the rise of Ancient Egypt along the Nile.