This is a vein of iron ore.

Image source: Ggia, WikiMedia
Image source: Ggia, WikiMedia

If you dig it out and purify it in a furnace, you’ll get iron.

Pure Iron. Image source: Alchemist-hp on WikiMedia
Pure Iron. Image source: Alchemist-hp on WikiMedia

It makes up 35% of the Earth’s mass, and most of it sunk into the Earth’s core when it was being formed.

It’s the sixth most abundant element in the universe, and there’s so much of it because it’s one of the major elements forged by stars as part of their natural lifespan.

Stars have made so much of it because it’s the final waste product that they make during their lifespan.

It’s a bit abstract, but this happens because iron has the highest ‘binding energy’ of all the elements. It means that iron lies at the bottom of a ‘valley’ of the elements.

The elements that come before iron are lighter than it, like hydrogen, carbon, and oxygen. Elements that come after it are heavier, like uranium.

Fusing lighter atoms together, like hydrogen, releases energy, like rolling a ball down the valley.


Atomic bombs work by splitting heavy atoms like uranium, which pushes them down the valley from the other direction.

Both methods extract energy from the atoms, but when you reach iron at the bottom you are stuck in a rut. You need to spend energy to fuse or split it’s atoms, like pushing the ball back up the slope.

Once a star starts producing a lot of iron, it’s a sign that it has used up all of its lighter atoms as fuel, and all that’s left is the waste that it can’t extract any energy from. The star is near the end of its life.

A star’s heat and light comes from fusing lighter elements like hydrogen and carbon, pushing them towards becoming iron
A star’s heat and light comes from fusing lighter elements like hydrogen and carbon, pushing them towards becoming iron

Depending on its mass, a star may then erupt as a supernova or a planetary nebulae, in which the chaos of the explosion will fuse a wild assortment of other elements together, creating the heavy elements like lead and uranium.

The explosion expels iron and other elements into space, where they will form new asteroids and planets. Iron is heavy, so it often sinks into their core, with some deposits left over in their crust.

On Earth, iron has been one of the most useful elements in human history. It’s been relatively straightforward for us to extract iron from the ground and melt it into new shapes, which has been hugely important for the development for our species.

Iron may be a dead end for stars, but it was the beginning for our advanced civilisation.

The ‘Iron Age’ defines the era of the ancient city states of Athens, Sparta, Troy, Carthage, and the Persian Empire. In mainland Europe, Celts built hill forts to defend their small agricultral communities. In India, the Vedas were being written. In every one of these cities you could hear the clank of the blacksmith’s anvil, working iron into swords, armour, and building equipment.

Iron is more difficult to work with than copper and bronze as it is melts at a higher temperature, so most early civilisations used them first before they developed the technology to use iron.

The earliest known iron goods were beads found in Egypt, made from metorite iron, but the first iron that was extracted from ore was in Mespotamia and Turkey. By modifying their furnaces to burn hotter and by adding charcoal, they sparked a chemical reaction which gave them lumps of iron which they beat into shape. Iron’s abundance, as well as the trade and cultural adoption of this technology, began the era known as the ‘Iron Age’.

Although iron is harder than metals like copper or bronze, it’s main disadvantage is that it is more brittle. Over time our use of iron has advanced to solve this problem. We’ve purified it then created mixtures with other things to create substances that are stronger than their constituent parts. Substituting charcoal with coke (the fuel that looks like coal) produces steel – one of the hardest substances yet developed.

Today iron is still heavily used. It’s inside stainless steel benches, cutlery, and appliances, in drill bits and in reinforced concrete, in ship hulls, and in the structural frames of cars, buildings, and aircraft.

Iron age weapons
Iron age weapons

It is a fascinating story from the big picture. Iron, as the waste product of stars, has been reused as the material backbone of an advanced species of ape for their civilisation.

It’s a reminder of the interconnectedness of everything in the cosmos, and how vast cosmic events billions of years in the past still influence our lives today.