La Times reported in 1991: Sphinx's New Riddle--Is It Older Than Experts Say? : Archeology: Geologists cite study of weathering patterns. But Egyptologists say findings can't be right.
Since then Robert Schoch, one of the geologists who led this investigation, has made a documentary with the guy who first noticed this (after reading about the water erosion patterns observation in an even earlier observer) John Anthony West. So here it is, the documentary in full followed by an outline of the theory using public domain pictures from Wikipedia. For more detailed analysis watch the video and read Robert Schock's write up on this here.
Mystery Of The Sphinx: This program presents geological evidence that the world's most famous monument, The Great Sphinx of Egypt, may be thousands of years older than we have been taught.
Outline of the basic theory;
As the Geologist, Robert M.Schoch, outlines in an article he posted on his website;
What I found most interesting is that the Sphinx seems to have been originally sculpted into a lion and then re-sculpted by a later civilization (the Pharaonic one) AFTER water and time had weathered the structure to such a degree that many of the lions head features were probably already gone.
Other Sphinxs of the Egyptian civilization were properly proportioned...
....as was the art of the prehistoric cultures surrounding that area and the Megaliths which seemed to have surrounded it as well. Saying the Egyptians ran out of rock is silly because they could have just made the whole structure smaller and kept it's proportions. In summary, the geological, historical, art and megalith culture evidence all align together to support the theory that the Sphinx had originally been carved out as a large lion.
Update! - 3/302017: Debunking Egyptologists Dr. Mark Lehner From the University Of Chicago & James F. Romano, Curator At The Brooklyn Museum