Short answers, pulled from the story.
Humphry Davy first isolated calcium in 1808 by electrolysis, using a mixture of calcium oxide and mercury(II) oxide on a platinum anode with a platinum wire cathode submerged in mercury. The process produced a calcium-mercury amalgam, from which distilling off the mercury yielded the metal. Davy also named the element.
The largest industrial use of calcium is in steelmaking, where it removes oxygen and sulfur impurities from molten steel, improving castability and mechanical properties. Calcium is also used in maintenance-free automotive batteries as a 0.1% calcium-lead alloy, as a reducing agent in producing metals such as chromium, zirconium, and uranium, and in drain cleaners where it generates heat and calcium hydroxide.
Calcium-48 is a doubly magic nucleus, with 20 protons and 28 neutrons both filling closed nuclear shells. It cannot undergo ordinary beta decay because the spin transition from zero to spin-6 is forbidden by conservation of angular momentum. Instead it undergoes double beta decay to titanium-48, making it the lightest known nuclide to exhibit that rare decay mode.
When plasma calcium levels fall, parathyroid hormone is secreted and draws calcium from kidney, gut, and bone cells into the blood. When levels rise, calcitonin secretion increases and counteracts the bone-forming action of parathyroid hormone. Vitamin D works alongside parathyroid hormone to enhance calcium deposition in bone.
Lime was used as a building material and as plaster for statues as far back as around 7000 BC. The first dated lime kiln, found at Khafajah in Mesopotamia, dates to around 2500 BC. Dehydrated gypsum was used in the construction of the Great Pyramid of Giza around the same period.
When bone formation exceeds bone resorption, the Ca/Ca ratio in soft tissue rises; when resorption outpaces formation, it falls. Because calcium minerals incorporate lighter isotopes preferentially, measuring the calcium isotopic composition of urine or blood can reflect changes in bone mineral balance, offering a potential early detection method for metabolic bone diseases like osteoporosis.