For about 4500 years, the mystery of how the Great Pyramids of Giza were built has endured. How did the Ancient Egyptians pull 70 ton granite slabs up an earthen ramp-without the benefit of wheels- 2/3 up the Great Pyramid? How did they carve granite, with pure copper? In some cases, adjacent blocks fit so well together that, even today, a human hair card cannot be inserted between them. Most important of all, to this day, Egyptologists have yet to explain how the tops of the pyramids were built. In this talk, I will present microstructural and other evidence that some of the pyramid blocks may have been cast using a combination of weathered limestone, diatomaceous earth and lime. The historical, archeological, and technological implications of our conclusions to today's world are truly profound and will be touched upon.