My nerdy side was very happy on this trip, as the area around Siwa is rich geologically. The portion of the Sahara Desert in which the Great Sand Sea and Siwa are situated was once submerged under ocean. They were exposed during the Post-Pliocene epoch, within the last 2 million years. In many places around Siwa you can see remains of the ancient seabed, including fish bones, corals, and shells, most of which has been bleached white through exposure to the elements. Just walking along, we found sand dollars, oysters, Cardium edule (common cockles), and scallop shells.
THINK FAST: What kind of rock is this? (ɹǝʍsuɐ ǝɥʇ ɹoɟ uʍop lloɹɔs)
I also found a small bone, which Zait thought came from a fox. All around there were rocky bluffs, too, worn down by millions of years of sand and wind. Zait said that you can find many other deposits around here, including petrified wood, shark bones, and corals. A hominid footprint was reportedly discovered close to Siwa Oasis in 2007 that, if the claims about it are true, would be the oldest fossilized hominid footprint ever found at 2-3 million years old.
Ma’alish, we didn’t get to see it, but it was still cool to think people or people-ish beings have been around here for such a long time.
THINK FAST answer: Sedimentary rock, of course! This type of rock is formed by layer upon layer of organic or mineral deposits settling on top of each other, often in bodies of water, as was the case here. The layers that form are called strata. Many of the shells here are all stuck together in conglomerate chunks. As part of the rock, these organic materials undergo the same processes as the rock. Any bits of soft tissue that were not previously eaten away by other animals are replaced with minerals and any cavities are filled up. In this case erosion has exposed the shells again for us to see.