The chemical reaction for CFC is: CCl3F = CCl2F + Cl. Uses. Due to their chemical properties, CFCs became useful as coolants and propellants. More commonly known as freon for refrigeration, CFCs are used extensively in appliances as a safe method of refrigeration. The other main use for CFCs has been as a propellant for aerosol cans.
The earliest known Egyptian pyramids are found at Saqqara, northwest of Memphis. The earliest among these is the Pyramid of Djoser (constructed 2630 BCâ2611 BC) which was built during the third dynasty. This pyramid and its surrounding complex were designed by the architect Imhotep, and are generally considered to be the world's oldest monumental structures constructed of dressed masonry.
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.