National Geographic News Feb 18th had a piece on exploration of underwater caves on the Yucatan peninsular where they have found some interesting objects (http://blogs.nationalgeographic.com ). In a deep pit that is known as the Black Hole they came across an Ice Age mastadon and bones of other Pleistocene fauna … and a human skull. To reach the Black Hole they travelled through 4000 feet of passages using underwater propulsion vehicles. The pit was some 200 feet deeper than the surrounding cave, and 120 feet in diameter.
The geology of Yucatan, and indeed the whole of the Caribbean basin, was remarkably different in the Ice Age. For example, Florida and the Gulf coast was much more extensive and the Bahamas was a large land mass, and Cuba much bigger than it is now. It seems that the Yucatan caves now underwater were above the ground. Formed out of limestone, a rock easily dissolved by rain water, it has a tendency to form caves and sink holes. There are lots of them in the Limestone Dales of Yorkshire, for example. At the end of the Ice Age these limestone caves were drowned by rising sea levels – or a changing geoid. The blog author says end of Pleistocene which is interesting. Did he say that not to be controversial as Clovis people were abroad before the Younger Dryas, or did he simply think sea levels rose slowly as the ice sheets melted. So far a laboratory date for the bones has not been done – it may be interesting. As an aside, Florida is also composed of a lot of limestone, former coral reefs that originally grew under the sea and therefore they were raised above ground at some later stage – in the case of Yucatan they were submerged after a spell above ground. So, if the skull was Ice Age, along with the mastadon, how did a human get to Mexico as early as that?