Is Earth’s Core Rusting?

A close view of rush on iron. Photo: Laitr Keiows/Wikimedia
Commons, CC BY-SA 4.0
Source: (https://bit.ly/3M5oMJZ)
-Deep below Earth’s surface – 2,900 km deep, to be precise
is a mass of mostly molten iron forming the planet’s outer core.
Could it rust as well?
-Scientists have recently shown that when iron meets moisture
at pressures close to 1 million atmospheres, the oxidation reaction
can form high-pressure rust.
-If rust is actually present where the outer core meets the mantle,
scientists may need to update their view of Earth’s interior and its
history.
-This rust could shed light on the deep-water cycle in the lower
mantle and on the enigmatic origins of small, thin regions atop
Earth’s fluid core that slow seismic waves.
-It could also help answer questions about the beginning of Earth’s
oxygen-rich atmosphere and how the atmospheric free oxygen level
reached the level of today.
Iron on Earth’s surface – whether in simple nails or mighty girders
reacts gradually when exposed to moist air or oxygenated water
through a chemical reaction known as oxidation. The reddish-brown
product of this reaction, rust, can consist of various forms of
hydrous (water-bearing) iron oxides and iron oxide-hydroxide
materials. In nature, the red rocks found in arid climes similarly
owe their color to the iron oxide mineral hematite, whereas in wetter
environments, iron ore minerals like hematite weather to form the
iron oxide-hydroxide mineral goethite (FeOOH).
Deep below Earth’s surface – 2,900 km deep, to be precise
is a mass of mostly molten iron forming the planet’s outer core.
Could it rust as well?
In experiments, scientists have recently shown that when iron meets
moisture – as water or in the form of hydroxyl-bearing minerals
at pressures close to 1 million atmospheres, similar to pressures in
the deep lower mantle, it forms iron peroxide or a high-pressure form
of iron oxide-hydroxide with the same structure as pyrite
(i.e., pyrite-type FeOOH) [Hu et al., 2016, Mao et al., 2017]. In
other words, the oxidation reactions in these experiments do,
indeed, form high-pressure rust.