Q&A for History of Mankind (7)
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This is the seventh Q&A for History of Mankind. Paid subscribers received an email soliciting questions and I got some.
I picked four that I think I can shed the most light upon. First, as tradition requires, I will comment upon a new piece of scholarship that pertains to an older post. In fact, this will be doubly (or even triply) traditional, since it goes back to the controversial issue of the relation between global warming and cooling and higher (or lower) levels of moisture and rainfall.
In the paper “An astronomical age-depth model and reconstruction of moisture availability in the sediments of Lake Chalco, central Mexico, using borehole logging data” (Quaternary Science Reviews, Vol. 294, 15.10.2022), Mehrdad Sardar Abadi et al show that the water level in the southern part of Lake Texcoco – which sometimes became seasonally disconnected from the main body of water, the reason why it’s referred to as “Lake Chalco,” now a tiny, shallow survivor – for the last million years oscillated in response to alternating warm and cool periods, with higher precipitation during the warm periods leading to higher levels and droughts connected to cooler periods leading to the water levels falling as low as a few meters only.
The importance of Lake Texcoco for Mexico’s and global history is pretty high, since it was along its shores that many of the most important Mesoamerican civilizations appeared, and many of their most important monuments were erected. As I discussed in How the Americas Diverged, Lake Texcoco, somewhat diminished by the 16th century AD, was dried first by the Aztecs and then by the Spaniards, and the modern megalopolis of Mexico City now fills the entire lake basin:
The list of great Mexican settlements around the Texcoco basin became impressive over the next millennia: Teotihuacan to the northeast, with Texcoco just south of it, and Azcapotzalco and Tlacopan to the west; the Aztecs' Tenochtitlan was founded on islands in the south-central part of the lake, while Xochimilco and Chalco rose to the south of the lake, close to the first city in Mesoamerica: Cuicuilco, where the the first stone monument of Mesoamerica was erected, a pyramid built in the middle of the first millennium BC.
Now for the questions:
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