Calcium Calcium Calcium is a chemical element with symbol Ca and atomic number 20. As an alkaline earth metal, calcium is a reactive metal that forms a dark oxide-nitride layer when exposed to air. Its physical and chemical properties are most similar to its heavier homologues strontium and barium. It is the fifth most abundant element in Earth's crust and the third most abundant metal, after iron and aluminium. The most common calcium compound on Earth is calcium carbonate, found in limestone and the fossilised remnants of early sea life; gypsum, anhydrite, fluorite, and apatite are also sources of calcium. The
Society for Scientific Exploration Society for Scientific Exploration The Society for Scientific Exploration, or SSE, is a group committed to studying fringe science. The opinions of the organization in regard to what are the proper limits of scientific exploration are often at odds with those of mainstream science. Critics argue that the SSE is devoted to disreputable ideas far outside the scientific mainstream. The Society was founded in 1982. Its first meeting took place at the University of Maryland, College Park in 1982. Of the SSE and its journal, journalist Michael D.. Lemonick writes, "Pretty much anything that might have shown up on The