New evidence that Egypt's Great Sphinx may be twice as old as had been thought has triggered a fierce argument between geologists who say it must be older and archeologists who say such a conclusion contradicts everything they know about ancient Egypt.
Geologists who presented their results at the Geological Society of America convention here Tuesday said that weathering patterns on the monument are characteristic of a period far older than had been believed. But archeologists and Egyptologists insist that even if the Sphinx is older than they think, it couldn't be much older because the people who lived in that region earlier could not have built it.
Most Egyptologists believe the Sphinx was built during the reign of the Pharaoh Khafre, also known as Chephren, about 2500 BC. But scientists who conducted a series of unprecedented studies at the Giza site told their colleagues that their evidence shows the Sphinx was there long before Khafre came to power. The evidence suggests that Khafre simply refurbished the Sphinx, which may have been several thousand years old, and incorporated it into his funereal complex.
Geologist Robert M. Schoch of Boston University told the meeting that his research suggests the Sphinx actually dates between 5000 and 7000 BC.
"And I'm trying to be conservative," he said in an interview. That would double the age of the Great Sphinx and make it the oldest monument in Egypt, he said.
But archeologist Carol Redmount of UC Berkeley, who specializes in Egyptian artifacts, said, "There's just no way that could be true." The people of that region would not have had the technology, the governing institutions or even the will to build such a structure thousands of years before Khafre's reign, she said.
Other Egyptologists who have looked at Schoch's work said they cannot explain the geological evidence, but they insist that the idea that the Sphinx is thousands of years older than they had thought does not match with the mountains of archeological research they have carried out in the region.
If the geologists are right, much of what the Egyptologists think they know would have to be wrong.
Schoch conducted the first seismic studies ever allowed at the site, and the research indicates that the limestone bed that surrounds the monument, part of which was exposed when the Sphinx was first carved, has weathered far longer than had been thought. In addition, erosional differences between the Sphinx and other structures of unambiguous origin also indicate the Sphinx is much older, Schoch said.
Joining him in the research were Thomas L. Dobecki, a Houston geophysicist, and Egyptologist John Anthony West of New York.
Schoch said Egyptologists believe Khafre built the Sphinx because it is part of the tomb complex that he had built for himself. Some believe the face of the Sphinx also resembles Khafre, but Schoch said he believes Khafre had the face refurbished when he incorporated the existing structure into his tomb.
The Sphinx is actually carved into the limestone bedrock, so it sits inside a ditch. The walls of the ditch offered Schoch his first tantalizing evidence. They are heavily weathered by water, suggesting that the ditch was dug before 3000 BC, when rainfall in the area was much higher than it has been in the last few thousand years.
He said another nearby structure, known to have been carved into a hillside during Khafre's era, does not show weathering that would be produced by water.
That indicates that the ditch around the Sphinx was carved out thousands of years earlier, he said.
Schoch also carried out seismic studies that reveal how sound waves travel through rock. Weathering creates pores in rocks, and the speed at which the waves travel can tell scientists about the porosity of the rock, and thus how much it has weathered. That, in turn, tells them how long it has been exposed to the elements.
The porosity of the rock on the floor of the ditch in front of the Sphinx has increased due to weathering to a depth of eight feet, he said. The same is true for the ditch on both sides of the monument.
But behind the Sphinx, where the ditch narrows to a small passage, the weathering only goes down to about four feet.
Schoch believes the "rump" of the Sphinx was carved out of the bedrock during Khafre's reign as part of his refurbishment, and thus is only about half the age of the ditch in front and on both sides of the monument.
If so, that would mean the head of the Sphinx had been there for thousands of years when Khafre came along.
But that conclusion flies in the face of "everything we know about ancient Egypt," said Berkeley's Redmount.
The Sphinx was created with technology that was far more advanced than other structures that are of known date, she said, and could not have preceded them by thousands of years.
In addition, "the rise of a complex society" that would have made such an undertaking possible did not begin until around 3200 BC, she said.
Only then did the area now known as Giza become important, so there would have been no reason to build such a monument in that area prior to that time, she added.
But Schoch believes the geological evidence shows the Sphinx may be as much as 9000 years old.
So the riddle continues.