Short answers, pulled from the story.
Iron is a chemical element with the symbol Fe and atomic number 26. It is a metal belonging to the first transition series and group 8 of the periodic table, and by mass it is the most common element on Earth.
Most of Earth's iron is concentrated in the inner and outer core, which together make up 35 percent of the planet's mass. In the crust, iron amounts to only about 5 percent of the mass, making it the fourth most abundant element there after oxygen, silicon, and aluminium.
Humans began mastering iron smelting in Eurasia during the 2nd millennium BC, with iron tools and weapons displacing copper alloys in some regions only around 1200 BC. The Hittites smelted iron between 1500 and 1200 BC, and after their empire fell in 1180 BC the practice spread, opening the Iron Age.
Iron rusts because it reacts readily with oxygen and water to form brown-to-black hydrated iron oxides. Unlike protective oxide layers on some metals, rust occupies more volume than the metal and flakes off, exposing fresh surface to keep corroding. Protecting iron from rust costs over 1 percent of the world's economy.
An adult human body contains about four grams of iron, roughly 0.005 percent of body weight, with about three quarters in hemoglobin. Iron carries oxygen in hemoglobin and stores it in myoglobin, and only about one milligram is absorbed each day because the body recycles its hemoglobin.
Ferrocene is a remarkably stable sandwich compound of iron discovered in 1951 by Pauson and Kealy and independently by Miller and colleagues. Its surprising molecular structure, determined a year later by Woodward and Wilkinson and by Fischer, transformed organometallic chemistry in the 1950s and remains a key tool in the field.