wood problem is responsible for the discrepancy, claiming the earlier dates were possibly derived from recycling large amounts of centuries-old wood and other earlier materials. Geopolymer Materials scientist Joseph Davidovits has claimed that the blocks of the pyramid are not carved stone, but mostly a form of limestone concrete and that they were "cast" as with modern concrete. According to this hypothesis, soft limestone with a high kaolinite content was quarried in the wadi on the south of the Giza Plateau. The limestone was then dissolved in large, Nile-fed pools until it became a watery slurry. Lime (found in the ash of cooking fires) and natron (also used by the Egyptians in mummification) were mixed in. The pools were then left to evaporate, leaving behind a moist, clay-like mixture. This wet "concrete" would be carried to the construction site where it would be packed into reusable wooden moulds and in a few days would undergo a chemical reaction similar to the curing of concrete. New blocks, he suggests, could be cast in place, on top of and pressed against the old blocks. Proof-of-concept tests using similar compounds were carried out at a geopolymer institute in northern France and it was found that a crew of five to ten, working with simple hand tools, could agglomerate a structure of five, 1.3 to 4.5 ton blocks in a couple of weeks. He also claims that the Famine Stele, along with other hieroglyphic texts, describe the technology of stone agglomeration. Davidovits's method is not accepted by the academic mainstream. His method does not explain the granite stones, weighing well over 10 tons, above the King's Chamber, which he agrees were carved. Geologists have carefully scrutinized Davidovits's suggested technique and concluded his concrete came from natural limestone quarried in the Mokattam Formation. However, Davidovits alleges that the bulk of the soft limestone came from the same natural Mokkatam Formation quarries found by geologists, and insists that ancient Egyptians used the soft marly layer instead of the hard layer to re-agglomerate stones. Davidovits's hypothesis gained support from Michel Barsoum, a materials science researcher. Michel Barsoum and his colleagues at Drexel University published their findings supporting Davidovits's hypothesis in the Journal of the American Ceramic Society in 2006. Using scanning electron microscopy, they discovered in samples of the limestone pyramid blocks mineral compounds and air bubbles that do not occur in natural limestone. Dipayan Jana, a