Iron–nickel alloy in the context of "Iron-making"

Ferrous metallurgy is the metallurgy of iron and its alloys. The earliest surviving prehistoric iron artifacts, from the 4th millennium BC in Egypt, were made from meteoritic iron-nickel. It is not known when or where the smelting of iron from ores began, but by the end of the 2nd millennium BC iron was being produced from iron ores in the region from Greece to India, The use of wrought iron (worked iron) was known by the 1st millennium BC, and its spread defined the Iron Age. During the medieval period, smiths in Europe found a way of producing wrought iron from cast iron, in this context known as pig iron, using finery forges. All these processes required charcoal as fuel.

By the 4th century BC southern India had started exporting wootz steel, with a carbon content between pig iron and wrought iron, to ancient China, Africa, the Middle East, and Europe. Archaeological evidence of cast iron appears in 5th-century BC China. New methods of producing it by carburizing bars of iron in the cementation process were devised in the 17th century. During the Industrial Revolution, new methods of producing bar iron emerged, by substituting charcoal in favor of coke, and these were later applied to produce steel, ushering in a new era of greatly increased use of iron and steel that some contemporaries described as a new "Iron Age".

Europa (/jʊˈroʊpə/ ) is the smallest and least massive of the four Galilean moons of Jupiter. It is observable from Earth with common binoculars and is a planetary-mass moon, slightly smaller and less massive than Earth's Moon. Europa is an icy moon, and, of the three icy Galilean moons, the closest orbiting Jupiter. As a result, it exhibits a relatively young surface, driven by tidal heating.

Probably having an iron–nickel core, it consists mainly of silicate rock, with a water-ice shell. It has a very thin atmosphere, composed primarily of oxygen. Its geologically young white-beige surface is striated by light tan cracks and streaks, with very few impact craters. In addition to Earth-bound telescope observations, Europa has been examined by a succession of space-probe flybys, the first occurring in the early 1970s. In September 2022, the Juno spacecraft flew within about 320 km (200 miles) of Europa for a more recent close-up view.

The core–mantle boundary (CMB) of Earth lies between the planet's silicate mantle and its liquid iron–nickel outer core, at a depth of 2,891 km (1,796 mi) below Earth's surface. The boundary is observed via the discontinuity in seismic wave velocities at that depth due to the differences between the acoustic impedances of the solid mantle and the molten outer core. P-wave velocities are much slower in the outer core than in the deep mantle while S-waves do not exist at all in the liquid portion of the core. Recent evidence suggests a distinct boundary layer directly above the CMB possibly made of a novel phase of the basic perovskite mineralogy of the deep mantle named post-perovskite. Seismic tomography studies have shown significant irregularities within the boundary zone and appear to be dominated by the African and Pacific large low-shear-velocity provinces (LLSVP).

The uppermost section of the outer core is thought to be about 500–1,800 K hotter than the overlying mantle, creating a thermal boundary layer. The boundary is thought to harbor topography, much like Earth's surface, that is supported by solid-state convection within the overlying mantle. Variations in the thermal properties of the CMB may affect how the outer core's iron-rich fluids flow, which are ultimately responsible for Earth's magnetic field.

Earth's inner core is the innermost geologic layer of the planet Earth. It is primarily a solid ball with a radius of about 1,230 km (760 mi), which is about 20% of Earth's radius or 70% of the Moon's radius.

There are no samples of the core accessible for direct measurement, as there are for Earth's mantle. The characteristics of the core have been deduced mostly from measurements of seismic waves and Earth's magnetic field. The inner core is believed to be composed of an iron–nickel alloy with some other elements. The temperature at its surface is estimated to be approximately 5,700 K (5,430 °C; 9,800 °F), about the temperature at the surface of the Sun.

Iron meteorites, also called siderites or ferrous meteorites, are a type of meteorite that consist overwhelmingly of an iron–nickel alloy known as meteoric iron that usually consists of two mineral phases: kamacite and taenite. Most iron meteorites originate from cores of planetesimals, with the exception of the IIE iron meteorite group.

The iron found in iron meteorites was one of the earliest sources of usable iron available to humans, due to the malleability and ductility of the meteoric iron, before the development of smelting that signaled the beginning of the Iron Age.