Short answers, pulled from the story.
Potassium is a soft, silvery-white alkali metal with atomic number 19 and chemical symbol K, derived from the Neo-Latin word kalium. The symbol was officially designated by the International Union of Pure and Applied Chemistry in its Gold Book.
Humphry Davy first isolated potassium in 1807 by running electricity from a voltaic pile through molten caustic potash (KOH). Potassium was the first metal ever isolated by electrolysis.
Potassium is a necessary element for plant growth, as Justus Liebig demonstrated in 1840. Agricultural fertilizers account for 95% of global potassium chemical production, with about 90% supplied as potassium chloride (KCl), representing the K in NPK fertilizers.
Naturally occurring potassium contains three isotopes: potassium-39 (93.3%), potassium-41 (6.7%), and potassium-40 (0.0117%). Potassium-40 is radioactive with a half-life of 1.25 billion years, and it is the most abundant radioisotope in the human body, with about 4,400 nuclei decaying per second in a 70 kg person.
Low blood potassium, called hypokalemia, is observed in 20% of hospital patients. Severe deficiency causes muscle weakness, respiratory paralysis, abnormal heart rhythms, and can be fatal if prolonged deprivation is not corrected.
Potassium-40 decays to stable argon-40 over time, and the ratio of these two isotopes in a rock sample reveals its age. Minerals well suited for this method include biotite, muscovite, metamorphic hornblende, and volcanic feldspar.