Earth’s inner core may be covered with huge amounts of bizarre iron ‘snow’

20 Dec 2019

Image: © Gus/

A new discovery shows that the Earth’s core is capped with iron ‘snow’, offering new clues about the forces that affect the entire planet.

While many hope for a white Christmas, deep within the Earth a very different type of snow forms. According to researchers from the US and China, it has been discovered that the Earth’s inner core is capped with large quantities of iron ‘snow’.

The snow is made from tiny particles of iron – significantly heavier than a regular snowflake – that fall from the outer core and pile on top of the inner core. These snowy peaks are enormous in size at more than 320km thick.

While scientists can’t directly sample the Earth’s core, it’s possible to record and analyse signals from seismic waves that pass through Earth.

However, aberrations between recent seismic wave data and the values that would be expected based on the current model of the Earth’s core have raised questions. For example, the waves move more slowly than expected as they pass through the base of the outer core and move faster than expected when travelling through the eastern hemisphere of the top inner core.

‘It’s sort of a bizarre thing’

The study, led by Sichuan University’s Youjun Zhang, proposed the iron snow-capped core as an explanation for the weird readings. Previous theories from the 1960s suggested the existence of a slurry layer existing between the inner and outer core, but prevailing knowledge about heat and pressure conditions in the core quashed that theory.

Now, the data from these latest experiments on core-like materials showed that iron crystallisation was possible and that about 15pc of the lowermost outer core could be made of iron snow.

Nick Dygert, an assistant professor at the University of Tennessee, said: “It’s sort of a bizarre thing to think about. You have crystals within the outer core snowing down onto the inner core over a distance of several hundred kilometres.”

The researchers said the process is similar to how rocks form inside volcanoes. In the study, they compared the iron snow with a process that happens inside magma chambers closer to the Earth’s surface, which involves minerals crystallising out of the melt and sticking together.

Given the core’s influence over the entire planet, understanding more about its composition and behaviour could help in understanding how these larger processes work.

Colm Gorey was a senior journalist with Silicon Republic