Cutting through the layers
Arguments proposing a date for the Sphinx that is much earlier than 4th Dynasty Egypt are based on a misreading of the Giza geology.
Giza geological formation
The Sphinx is carved from the natural limestone of the Giza Plateau known as the Mokkatam Formation. An Eocene-period sea retreated 50 million years ago, leaving an embankment that became the north-northwest part of the Giza Plateau.
As the sea receded, a shallow lagoon formed above a shoal and coral reef in what is now the south-southeast part of the Plateau. Over millions of years, carbonate mud petrified to become the layers from which the pyramid builders quarried limestone blocks and from which they carved the Sphinx.
The Sphinx within the Giza geology
The Sphinx is cut from the lowest layers of the Mokkatam Formation, those layers lying directly on the harder petrified reef. We label the Sphinx geological layers Member I, Member II, and Member III after the work of geologist K. Lal Gauri (K.L. Gauri, Geoarchaeology, 1995).
The lowest stratum of the statue is the hard, brittle rock of the ancient reef, Member I. This layer rises to a height of 12 feet at the Sphinx’s rump and only two to three feet at the paws.
Most of the Sphinx body is cut into Member II, seven layers that alternate softer and harder as they rise in elevation.
Member III, from which the neck and head are carved, is softer at the neck and harder at the head. This is good building stone, which is why most of it was quarried away. Member III’s durability explains the remarkable preservation of the Sphinx’s face while the statue’s body has been ravaged by weathering.
One popular theory about an older age for the Sphinx states that an Old Kingdom tomb cut from the “exact same layers as the Sphinx” shows a pattern of weathering that is different than that of the Sphinx quarry walls. The theory posits that the Sphinx and the exterior of the tomb of Debehen (contemporary with Menkaure, 2490-2472 BC) should have weathered exactly the same unless the Sphinx was older and was weathered by water during a wetter period.
In fact, the tomb of Debehen is some 418 meters (1371 feet) west-southwest of the Sphinx and approximately 27 meters (88.5 feet) higher in elevation; it’s not in the same series of layers. The difference in weathering is due to different physical properties of the rock and to different conditions of the environment, not the age of the monuments.
Until recent years, the Sphinx was still disintegrating. In the 1980s, two sizeable stones fell from the statue: masonry veneer from the left hind paw in 1981 and a large piece of bedrock from the right shoulder in 1988.
On any windy day, you can watch large flakes of limestone blow off the walls of the Sphinx quarry. The Supreme Council of Antiquities’ decade-long restoration in the 1990s was only the latest of the repairs to the Sphinx that began at least in the New Kingdom (1550-1070 BC).
If the Sphinx erodes so rapidly, there’s no requirement to set an age older than 4,500 years to explain its present state of deterioration. Aside from the geology, we can present other evidence that ties the Sphinx to Pharaoh Khafre’s building program at Giza.
(See also, Hawass and Lehner, “The Sphinx: Who built it and why?,”) Archaeology, Sept/Oct 1994, pp. 30.