Iron

Category: transition metal Atomic number: 26 Colour: silvery grey Melting point: 1,538°C (2,800°F) Boiling point: 2,861°C (5,182°F) First identified: ancient civilizations

One of the most important metals in human history, iron is also the most plentiful element (by mass) on Earth, partly because the planet’s core is largely made up of it. In the process of the Earth’s formation, as a swirl of dust and gas was gradually compressed from a protoplanetary disc into a planet, the heaviest elements naturally gathered in the centre and iron ended up forming a solid, inner core and a molten liquid outer core. It is the iron core that gives the planet a magnetic field – there are magnetic poles at the north and south of the globe, and the field reaches out into space, deflecting potentially harmful solar winds and radiation.

The first iron artefacts date back to the ancient Egyptian period, but it was the Hittite civilization of Asia (in present-day Turkey) that discovered how to smelt the metal, which made it far easier to work, in about 1500 BC. The Hittites kept their discovery secret for centuries, but after their empire was invaded in 1200 BC, the ironmakers scattered, taking their skills with them and thus triggering the Iron Age.

Iron can be cast, welded or machined into a huge variety of forms – at various points throughout history, people developed the ability to create stronger, less brittle forms of iron by smelting it with carbon or other metals. The legendary metal, Damascus steel, was astonishingly hard, shatterproof and sharp, probably due to the fact that there was a proportion of vanadium in the ore used to make it (which came from the Indian subcontinent). It was the discovery of more efficient methods of production in the seventeenth century that triggered the huge surge of new technology, known as the Industrial Revolution, and this was developed further after the invention of the Bessemer process (a large-scale steel production method) in 1856. Since then it has been used to make everything from bridges to ships, skyscrapers to cars, tools to paper clips.

The biggest drawback to iron is how easily it rusts when it comes into contact with oxygen. This problem can be mitigated in a variety of ways, including coating the iron (or steel) with tin, or zinc (in which case it is ‘galvanized’), or alloying it with nickel to make it resistant to corrosion.

Iron is another element that is crucial to life – it is present in our body in a variety of forms, notably in the haemoglobin that transports oxygen through the blood. A lack of iron in the diet leads to lower red blood cell production and anaemia, in which you become tired and breathless. The best sources of iron are red meat and liver, certain dried fruits, bread and eggs.

All elements heavier than iron, including gold and lead, were originally formed exclusively in supernovae rather than stars. Stars simply aren’t hot enough to make the heavier elements.