This entry is part 3 of 3 in the series Structure of the Earth Theme Week

The Iron Catastrophe


Everyone alive today owes their existence to a catastrophe.

To explain that seemingly paradoxical statement, let’s foray into a brief overview of the universe, our sun, and the planet, courtesy of Columbia University.

Somewhere around 13.8 billion years ago, the Big Bang kicked things off. There was hydrogen and only hydrogen. The hydrogen congealed into big orbs of hydrogen. Fusion reactions in the orbs began, forming the first stars. These stars began to produce the other elements up to the weight of iron. About 5 or 6 billion years ago, a star ran out of hydrogen fuel and went supernova. This explosion created and spewed out all the other elements.

Timeline after the Big Bang - image by NASA

The dispersion of elements eventually coalesced into giant disks. The centers of these discs became superheated, forming a new star. One of these stars was our sun. From the remaining matter in the disk, planets consolidated 

As the mass of our planet slowly grew, thanks to colliding with more and more particles in the nebular cloud, its gravitational force also increased. This growing force compressed the planet. On our timeline, we’ve moved to about 4.5 billion years ago. The compression began to heat the interior of the planet. Coupled with decay from all the new radioactive elements swirling around, the inner portion of the nascent planet began to melt.

Iron was the heaviest of the commonly available elements, so as the Earth began to melt, droplets of molten iron sunk to the center of the globe. The heating gradually continued until a critical condition occurred. The sinking of the dense iron’s potential gravitational energy morphed into a runaway train. Our planet’s temperature reached heights above the melting points of most of its components. The result was a molten iron core, covered by silicate magma.

This event, which happened about 500 million years after the protoplanet was birthed, is called the Iron Catastrophe.

What a molten earth might have looked like in the early days - image by Sutori

Catastrophe usually denotes something bad. In this case, the word refers more to scale. The original etymology of “catastrophe” means “reversal of what is expected,” from the denouement of a play. In the mid-1700s it took on the definition of “sudden disaster.” In the case of the early planet, the scope of the iron consolidation was extraordinary in its totality and its suddenness.

We started this article with the thesis that we owe our lives to a catastrophe. Catastrophes definitely do not connote something good, so what’s going on with that?

The Iron Catastrophe turned Earth into a giant, spinning orb of super-hot metal. Giant, spinning orbs of super-hot metal create magnetic fields. The resulting magnetosphere is a massive, invisible shield that keeps life on Earth pumping!

An artist's rendering of the structure of a magnetosphere - image by Dennis Gallagher

Without a magnetosphere, the planet would be raked by the solar wind and much of the radiation that emanates from our star. The planet’s magnetic field creates a bubble in space, without which we would fry and life could not exist.

To see evidence of the possible wasteland our planet would become without the magnetosphere, we need only look to our next-door neighbor. Astronomers believe Mars evolved similarly to our planet, perhaps even undergoing its own Iron Catastrophe. But, at some point, the dynamo at the core of the red planet fizzled. The magnetosphere of Mars vanished, which meant radiation could scour the planet. Today, Mars cannot sustain life naturally.

Sometimes catastrophes end in barren expanse; sometimes they end in verdant kaleidoscope!

Further Reading and Exploration

Lecture on Big Bang and planet creation – Columbia University

Earth formation – Khan Academy

What Happened During The Iron Catastrophe – World Atlas


Magnetospheres – NASA

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