Chlorofluorocarbon: Chlorofluorocarbon (CFC), any of several organic compounds composed of carbon, fluorine, and chlorine. When CFCs also contain hydrogen in place of one or more chlorines, they are called hydrochlorofluorocarbons, or HCFCs. CFCs are also called Freons, a trademark of the E.I. du Pont de Nemours & Company in Wilmington, Del. CFCs were originally developed as refrigerants during the 1930s. Some of these compounds, especially trichlorofluoromethane (CFC-11) and dichlorodifluoromethane (CFC-12), found use as aerosol-spray propellants, solvents, and foam-blowing agents.
The Egyptians started building the Great Pyramid of Giza on August 23, 2470 B.C., according to controversial new research that attempts to place an exact date on the start of the ancient construction project. Enlarge Photo. Printer Friendly. Email to a Friend.
On Wrangel Island, an island in the arctic ocean, they lasted until around 2000 BCE (possibly as late as 1600 BCE). The first pyramid in Egypt, the Step Pyramid at Saqarra, was built between 2667 and 2648 BCE. Work on the Great Pyramid at Giza, for comparison, began around 2580 BCE. This means that pyramids and mammoths technically overlap in time, though the two never met. Around 30,000 years ago, mammoth could have been found as far south as Spain and Italy (fossils have been found in these areas), though never as far south as Egypt and certainly not in the time when the pyramids were built.