You may have seen this item enthusiastically recently reported on the Ancient Code site: “Scientists: Geological evidence shows the Great Sphinx is 800,000 years old.” Ancient Code is a repository of fringe archaeology. Surprise!
What Ancient Code doesn’t tell you is revealed in this essay by Jason Colavito: “Why Are So Many Interested Now in a 2008 Claim about the Sphinx’s Age? Colavito writes in part:
. . . the two authors did not conduct any field testing to reach their conclusions. Instead, they say that they re-dated the monument based on a “visual investigation” (i.e. visiting the Sphinx and looking at it) and “reading the literary sources.” They based their conclusion on a comparison of the Sphinx, in a desert environment, with rock walls around the Black Sea, in an environment that differs in pretty much every conceivable way. Nevertheless, they argue that the undulating pattern of erosion on the Sphinx is not the work of wind and sand working differentially on rock layers of different hardness but rather the work of waves that accomplished the same task in a time when Giza was flooded.
They conclude that when the Sphinx was carved, Giza must have been like the Black Sea is today, and therefore this could only have occurred 750,000 years ago. The argument runs thus: If we assume that waves were necessary to create the erosion pattern (because it looks similar to the erosion pattern on the Black Sea coast), then we would need a water level at least 160 m higher than the current sea level to flood the Sphinx;therefore, this could only have occurred 750,000 years ago, the last time the sea was so high. As you can see, the problem is the initial if, based as it is on a “looks like therefore is” line of reasoning, without geochemical or any other type of proof to substantiate it.
They also do not explain how the Sphinx, which continues to deteriorate and erode in the desert environment to this day, survived 750,000 years almost intact while undergoing much more damaging erosion in historical times except that they feel that sand erosion, which is known to have occurred, was much more damaging than their proposed hundreds of thousands of years of water erosion.
When you drill down into their paper, it becomes clear that they never considered alternative hypotheses, nor did they attempt to find proof that only submersion in a giant lake could achieve the erosion they describe.