The Great Sphinx of Giza is carved directly out of the bedrock of the Giza plateau. To make it, the builders cut away the surrounding limestone, leaving the figure standing in a sunken enclosure. That enclosure, and the body of the Sphinx itself, are deeply weathered: rounded, furrowed, and fissured in a way that anyone standing in front of them can see.

Egyptologists attribute the Sphinx to the pharaoh Khafre, around 2500 BC. In the early 1990s, a geologist looked at the weathering and asked a simple question: what kind of weather does that? His answer started one of the longest running arguments in alternative chronology.

The Origins of the Idea

The idea did not begin with a geologist. In the 1950s, the French writer René Schwaller de Lubicz suggested that the Sphinx’s body showed signs of water erosion. In 1979, John Anthony West developed the idea in his book Serpent in the Sky, attributing the damage to ancient floods.

West needed a geologist to test it. In 1990 he brought Robert Schoch, a geologist at Boston University, to Giza. Schoch went expecting to find the idea wrong. Instead, he came away convinced the weathering was caused by water, and he presented his case in 1991, followed by a 1992 paper, “Redating the Great Sphinx of Giza.”

Schoch’s Case

Schoch’s argument rests on the difference between kinds of weathering:

  • Vertical, not horizontal. Wind and blowing sand tend to cut horizontal grooves into soft rock layers. The walls of the Sphinx enclosure instead show deep, rounded, vertical fissures and an undulating profile, which Schoch argues is the signature of rainwater running down the rock over a very long time.
  • Concentrated where water would run. The weathering is heaviest where runoff would have been strongest as rain poured over the plateau and into the enclosure.
  • Different from nearby tombs. Schoch argues that Old Kingdom tombs cut into similar rock nearby, which are known to date from Khafre’s time, show much less of this kind of weathering.

The key step is dating. Egypt received significant rainfall in the past, during the period when the Sahara was green. If the Sphinx shows heavy rain erosion, Schoch reasoned, it must have been carved while that rain was still falling, before the region dried. His first estimate pushed the Sphinx back to at least 5000 to 7000 BC. In later work, including his 2012 book Forgotten Civilization, he moved toward an even earlier date, around 9700 BC, at the end of the last Ice Age.

A date that early would make the Sphinx thousands of years older than any other monumental structure in Egypt, and imply a sophisticated culture in the Nile valley long before the pharaohs.

The Replies

Schoch’s claim drew sustained responses from both Egyptologists and other geologists. The main counterarguments are these:

A different kind of weathering. Several geologists argue that the damage comes not from rain but from salt weathering, known technically as haloclasty. In this process, moisture from dew, occasional rain, or even damp sand soaks into the porous limestone, dissolves salts, and then evaporates, so that growing salt crystals break the rock apart from inside. K. Lal Gauri and colleagues made this case in 1995. James Harrell argued that the sand which buried the Sphinx for much of its history held moisture against the rock, producing the same effect. Salt weathering can create rounded, fissured surfaces that look like water erosion.

Poor quality rock. Egyptologist Zahi Hawass and others note that the lower layers of the Sphinx are carved from particularly soft, poor quality limestone that deteriorates quickly. On this view, 4,500 years of ordinary weathering, plus repeated ancient repairs, are enough to explain the damage.

The archaeology fits Khafre. Mark Lehner, who spent years mapping the Sphinx, argues that the enclosure, the Sphinx Temple, and Khafre’s causeway and Valley Temple form a single, planned complex. The Sphinx Temple was built using the remains of the Valley Temple, and the enclosure’s southern wall follows the angle of Khafre’s causeway. A 2014 luminescence dating study placed both temples in the mid to late third millennium BC, consistent with Khafre.

When did the rain stop? Schoch’s dating assumes that heavy rainfall ended well before Khafre’s reign. But in 2014, geoarchaeologists Fabian Welc and Leszek Marks reported evidence of significant rains in the region until around 2200 BC, during and after the pyramid age. If rain continued into Khafre’s time, rain erosion would not require an earlier date at all.

Where is everyone else? The archaeological objection, voiced by Kenneth Feder among others, is that there is no other evidence of a society in Egypt capable of carving the Sphinx before about 3000 BC: no settlements, tools, pottery, or other monuments of the right age and scale.

The Middle Position

Not every geologist who takes the water erosion seriously accepts Schoch’s dates. British geologist Colin Reader argued that the weathering is better explained by surface runoff draining across the plateau into the enclosure, which would have been heaviest before later Old Kingdom quarrying changed the landscape. Reader concluded the Sphinx might be somewhat older than Khafre, possibly from Egypt’s Early Dynastic period, a few centuries earlier, but not thousands of years older. That position is far more modest than Schoch’s, and still controversial.

A New Twist in 2025

At the Geological Society of America’s 2025 annual meeting, geologist Robert Schneiker offered a different explanation entirely. He argued that there is “very little erosion on the Sphinx” at all. In his model, the builders pounded back the soft limestone of the body and covered it with a veneer of higher quality limestone blocks, which were then sculpted. Sand buried the figure for most of its history, and when the veneer was later stripped, the rough, pounded core was exposed. What looks like millennia of rain damage, he suggests, “has been misidentified as erosion.”

It is one conference presentation, not a published study, and it will need detailed testing. But it shows that the debate is still producing new ideas more than three decades on.

Where It Stands

The scorecard looks like this:

QuestionWhere it stands
Is the Sphinx enclosure heavily weathered?Yes. Everyone agrees.
Is the weathering pattern unusual?Yes. The unusual pattern is why the debate exists.
Was it caused by rain?Contested. Rain, runoff, salt weathering, and construction methods all have defenders.
Did heavy rain end before Khafre?Doubtful. Evidence suggests rains continued until about 2200 BC.
Does the archaeology support a much older Sphinx?No. The surrounding complex fits Khafre, and no earlier culture capable of the work has been found.

The mainstream view remains that the Sphinx was carved under Khafre, and the water erosion hypothesis is widely classed as fringe. Our view is a little more nuanced. Schoch did something valuable: he took a physical observation seriously and asked whether the accepted story fully explained it. That question has never been completely closed, and the fact that geologists are still proposing new explanations in 2025 shows the weathering is genuinely puzzling.

But a puzzling observation is not yet evidence of a lost civilization. For Schoch’s date to win the argument, it would need support from outside the weathering itself: datable remains, tools, or structures from 7000 to 10,000 BC in the Nile valley. Until then, the honest conclusion is that the Sphinx’s weathering is a real anomaly with several competing explanations, and the strongest evidence still points to Khafre’s era.

For further reading, Schoch’s Forgotten Civilization and West’s Serpent in the Sky are listed on our Resources page.

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