How old is it?
That evidence consists of the weathering patterns on and about the Sphinx which is indicative of "water erosion". The problem here is that there has been no significant rainfall in the area since the Sahara desert was a fertile savannah (as evidenced by cave paintings).
For those not familiar with the placement of the sphinx, it is in a carved depression ... kind of a three sided box with stone walls about ten feet high ... a short distance from the Nile with the Giza pyramids in back of it. During most of its existence, the lion body has been covered by sand with just the head sticking out.
The walls definitely show this type of erosion (and erosion form the Nile has been ruled out) ... so there is no question that the lower part (the lion body) was carved out at the time of that erosion. The Egyptologist on the program clearly demonstrated a degree of fear and could only appeal to "authority", i.e. Egyptologists are very careful, scientific fellows and couldn't possibly be mistaken. The context of the documentary is somewhat obscure, so I can't say that some statements weren't taken out of context (which is often the case on TV).
Something which wasn't stated ...
Although they said that the head had probably been recarved, no note was made of the following.
That the head is artisticly incompatible with the body. It does not integrate properly either in size or design.
For instance, though I never knew that the sphinx was in an "enclosure" till I saw this show, I have always wondered why the head is sooooooo damn small. It reminds me of a scene at the end of the movie "Beetlejuice" where Michael Keaton is sitting next to a witch doctor and gets his head shrunk. The sphinx' head is way too small to have been "passed" on by a king or emperor at the design stage. That is, no one would OK this massive and expensive work with such poorly drawn proportions.
And, the style seems completely different. Absolutely foreign.
So here's the theory
Some "Saharan" culture, of which we know nothing, built this structure as a big lion ... a common, "macho" animal of the area (and therefore worthy of being immortalized). It rains a lot and causes the weathering. Then the Sahara goes dry and the civilization disappears. The head sticks out from the sand and some thousands of years later, the new locals carve it into the head of "Pharoah". Now it's much smaller because they cut away more stone ... and ... the head was subject to wind erosion for thousands of years while the body is protected ... hence, the "Keaton head".
Now, they find out that the head is attached to the body by clearing away the sand to see how deep it goes.
"Wow! The body of a lion ... our Pharoah has the body of a lion ... what an interesting thesis ... let's incorporate it into our religion!"So now they have this cool idea that the mangods have animal heads and man bodies or vice versa. Combo style Gods ... and this is taken up by subsequent cultures.
What is this ancient culture and ... where is to be found its remains?
Well, it may be that this is the only thing they ever made. Probably untrue ... If you can work stone this well, you probably have buildings also. The place to look is where there were ancient rivers ... cities or cultural centers will be at the forks in river systems ... under the sand ... to be located only with ground penetrating radar ... someday.
Though there is no present evidence of a "high" Saharan culture, we know there were people out there. If you look at Russia, you know there were people out there too during Roman times but there is no evidence of an advanced stone building culture in that area from that time. Yet there were stone building cultures elsewhere ... these "barbarians" sacked them.
I think this finding of water erosion on the Sphinx is going to lead to something interesting sometime in the near future. I look forward to it.