The single most astonishing session for me was Stefan Kröpelin's "Miracle of the Sahara." Kröpelin compressed 40 years of research and exploration into a whirlwind tour of the Sahara's mysteries and what it is like to do science there. Summarizing conditions, he noted, "Sometimes, you get stuck hundreds of times per day… and the real problem isn't the heat; it's the cold." The size of the U.S, Kröpelin's Sahara is full of mysteries: Gilf Kebir, a sand plateau atop an ancient fluvial system in Southwest Egypt holds rock art from the middle Holocene, over 10,000 figures in one cave alone. The Wadi Howar was thought by Herodotus to be the source of the Nile; now it is vast desert, but in it's heart is the Ounianga Kebir, a cluster of freshwater aquifer-fed "gravity lakes," and home to seven crocodiles, the remnant of an Ice Age population, now isolated from other crocs by hundreds of miles of searing desert.
But the biggest mystery was sitting right in front of Kröpelin as he spoke. It was a chunk of "Libyan Desert Glass," 28 million-year-old fused glass the color of pale emerald and the purest natural glass in the world. Discovered by Europeans in 1932, the stuff is strewn across a vast area of desert at the edge of Egypt's great Sand Sea. Kröpelin's chunk looked like a glass meteorite, complete with ablation regmaglypts, suggesting that the glass was created by a meteor strike that liquefied the surface rocks in a process not unlike that which created tektite strewn-fields elsewhere on the earth. Except… no one has found a crater. Perhaps the glass is a radiative melt artifact of a Tunguska-like airburst? Others speculate that it is hydrovolcanic in origin, but no has found a volcanic source.
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