According to geologist August Matthusen,
Schoch's argument hinges on weathering and weathering morphologies of the in situ rock not erosion. Erosion is the process which removes material; weathering is the process which degrades the rock in place. Schoch has indicated that the rounded profile of some of the Sphinx was due to "precipitation-induced weathering" rather than "wind-induced weathering" which supposedly produced a straight profile on other weathered rock structures. Supposedly there was only sufficient water to produce this "precipitation-induced weathering" during a wet period some 7000 years ago. Thus Schoch makes his argument for increased antiquity of the Sphinx (i.e, it had to exist more than 7000 years ago rather than the approx 4500 years ago to which it is normally dated). West has pushed this age back further and has tried to relate it to Atlanteans.Schoch's ideas ignore several things. "Precipitation-induced weathering" versus "wind-induced weathering" producing different weathering morphologies is not an accepted idea, rather variations in the rock usually account for the different weathering morphologies. Schoch does not test his idea to determine if the rounded and straight morphologies result from precipitation and wind respectively. He just states that they do. If the "precipitation-induced weathering" occurred 7000 years ago and the "wind-induced weathering" occurred on structures 4500 years old, why didn't the "wind-induced weathering" obliterate the older "precipitation-induced weathering?" Schoch also ignores the possibility that other processes could cause the weathering morphology.
Geologists have been working on the Sphinx for years studying its rapid weathering and have found that the rapid weathering (which predates high atmospheric acid content) is due to formation of salt crystals in the rock pores which causes exfoliation due to hydrostatic pressure (see papers by Punuru et al., 1990; Chowdhury et al., 1990; Guari et al., 1990; and Guari et al., 1995). This exfoliation results in a rounded profile similar to that which Schoch indicates could only be due to "precipitation-induced weathering." All in all, Schoch seems to have focused on one explanation and ignored several other working hypotheses which explain the phenomenon much more concisely than having to resort to the Sphinx being carved 2500 years before there is a well recognized civilization in Egypt (not to mention the Atlanteans). Because, an additional point to consider is: how did a civilization capable of carving a monolithic structure come into being, which vanished without any other trace? As many other people have pointed out: what happened to their pots and pot sherds, stoneworking tools, and evidence for their residences? I'd suggest reviewing the Gauri et al. (1995) paper for a more detailed explanation of the controversey and the evidence.
Chowdhury, A.N., A.R. Punuru, and K.L. Gauri, 1990. Weathering of Limestone Beds at the Great Sphinx; Environmental Geology and Water Science, Vol. 15, No. 3, pp. 217-225.
Gauri, K.L., A.N. Chowdhury, N.P. Kulshreshtha, and A. R. Punuru, 1990. Geologic Features and Durability of Limestones at the Sphinx; Environmental Geology and Water Science, Vol. 16, No. 1, pp. 57-62.
Punuru, A.R., A.N. Chowdhury, N.P. Kulshreshtha, and K.L. Gauri, 1990. Control of Porosity on Durability of Limestones at the Great Sphinx, Egypt; Environmental Geology and Water Science, Vol. 15, No. 3, pp. 225-232.
Guari, K. L., J.J. Sinai, and J.K. Bandyopadhyay, 1995. Geologic Weathering and its Implications on the Age of the Sphinx; Geoarchaeology, Vol 10, No. 2, pp. 119-133.
Salt crystal exfoliation may have had a role in the appearance of both the Sphinx and its enclosure walls. August Matthusen explains:
Salt crystal exfoliation isn't a wind induced process. The salts (halite and gypsum) are naturally present in the pores of the rock probably from when the rocks were originally deposited in sea water. The naturally present salts are dissolved when dew condenses on the rock at night. The pores help draw water into them by capillary action (like how water rises slightly higher in a drinking straw when a straw is placed in liquid; as the straw or pore gets smaller the capillary action gets greater). Also salts like halite are hygroscopic, a property which allows the salts to condense water at a moisture level which would be insufficient for dew to form.During the cooler nights the water in the atmosphere condenses it is drawn into the pores and dissolves the salts. When day time comes and temperatures rise this liquid with the dissolved salts starts to evaporate. The salts crystallize as the water evaporates. The crystals push against the side of the pore and the crystals also push against the remaining liquid causing the liquid to push against the walls of the pore. This repeated process causes the rock to beak down when the pressure exceeds the strength of the stone. This processes occurs above ground.
A few more bits on salt crystal weathering:
In D.F.Ritter (1978) Process Geomorphology on page 134: "Minerals can also grow in rock spaces, with results similar to those of frost action, as figure 4.7 shows. Most commonly the process functions when percolating fluids evaporate within the pores, giving rise to supersaturated conditions and eventual precipitation of minerals. [Note that here precipitation of minerals is referring to crystallization not rainfall.]
"The pressures exerted in crystallization are probably greater than those produced by ice, but their absolute values depend upon the concentration of the ionic constituents in the solution. The most common precipitates are sulfates, carbonates, and chlorides of very mobile cations (Ca, Na, Mg, K) and the process is therefore more prone to operate in arid and semiarid regions where the ions are rendered immobile by insufficient leaching."
In Earth by Frank Press and Raymond Siever (1978, second edition) on page 99: "Crystallization of such mineral as salt or gypsum, which may follow the evaporation of salty solutions that infiltrated the cracks, may also wedge fractures open."
In Environmental Geoscience: Interaction between Natural Systems and Man by Strahler and Strahler (1973) on page 267: "Closely related to the growth of ice crystals is the weathering process of rock disintegration by growth of salt crystals. This process operates extensively in dry climates and is responsible for many of the niches, shallow caves, rock arches, and pits seen in sandstone formations. During long drought periods, ground water is drawn to the surface of the rock by capillary force. As evaporation of the water takes place in the porous outer zone of the sandstone, tiny crystals of salts are left behind. Salts involved in this process are commonly gypsum, calcite, soda niter (sodium nitrate), and hydrous sulfates of sodium and magnesium. The growth force of these crystals is capable of producing a granular disintegration of the sandstone, which crumbles into sand and is swept away by wind and rain." and continues on page 267 and 268: "Salt crystallization also acts adversely upon masonry buildings and highways. Brick and concrete in contact with moist soil are highly susceptible to granular disintegration from this cause. The salt crystals will be seen as a soft, white, fibrous layer on basement floors and walls. Salts are commonly hydrous calcium sulfate (gypsum), sodium sulfate, or magnesium sulfate."
In Earth, Time, and Life by Charles W. Barnes (1980) on page 96: "Ice is not the only crystal whose growth causes the destruction of rock. Ordinary rock salt and its soluble associates may crystallize within cracks and pores of rock near the surface, and the effects will be like those of ice. Salt weathering has been described in coastal areas, where crystals of salt from seawater help wedge rocks apart, and from arid areas as diverse as Arabia and Antarctica."