The Earth's core is growing asymmetrically and we don't know why. We are at a turning point for the study of Earth's magnetism
Every year the iron core of planet Earth expands by about a millimeter: this is due to the cooling of the deepest layers of the Earth's crust, which lose heat and become solid.
A recent study, published in Nature Geoscience, seems to point to unexplained evidence for the first time: one side of the Earth's core appears to be growing faster than the other.
In the Earth's core
The Earth's iron core has a radius of more than 1,200 kilometers, and is at a temperature bordering on 500°C. It is also known as the solid core, because despite the very high temperatures, similar to those found on the surface of the Sun, the strong pressure does not allow the iron-nickel alloy to melt completely.
The Earth's solid core was formed between 1.5 and 0.5 billion years ago and is now affected by a physiological process of heat loss and "crystallization": as it cools, the outer layers of the ferrous core solidify, becoming part of the solid core.
But this growth appears evidently asymmetrical: nearly 3 thousand kilometers below the Banda Sea in Indonesia, 60% more ferrous crystals are forming than are occurring on the other side of the planet.
Daniel Frost, author of the study, emphasizes the importance of the discovery, recalling that the activity of the Earth's solid core vitally affects the existence on our planet: the geodynamon, that bubbling of liquid iron that generates the magnetic field that allows life on Earth, depends essentially on what happens inside the iron core.
It is precisely the phenomenon of heat release typical of cooling that generates the convective motion on which depends the existence of the Earth's magnetic field.
In the same way, says Frost, "everything is influenced by what happens in the upper layers": if the outer core and then the crust were not able to receive the heat released in the cooling phase, this process would not be possible.
L’asimmetria è inspiegabile
Il punto in cui è stata registrata la crescita massima del nucleo, negli abissi del mare indonesiano, corrisponde ad una importante area di subduzione, ovverosia una di quelle zone in cui le placche tettoniche scorrono una sotto l’altra per scivolare nelle profondità del mantello.
Ciò significa che grossi blocchi freddi di placche tettoniche vanno avvicinandosi al mantello, inevitabilmente raffreddandone la temperatura: "è come gettare cubetti di ghiaccio nel mantello", spiega ironicamente Frost.
Questa però è una spiegazione decisamente troppo debole per giustificare la crescita asimmetrica del nucleo ferroso: è piuttosto improbabile che il calore proveniente dalle viscere del nostro pianeta venga dissipato in linea retta.
According to Frost and the other authors of the study, the cold Indonesian crust might be more likely to cause cooling below China, or Saudi Arabia.
The asymmetry thus remains without an unambiguous explanation at the moment, and it is not known whether it could lead to a deformation of the Earth's ferrous core over the eons. What is certain is that this study opens the way to important discoveries about the Earth's magnetism.
The asymmetry of core growth, in fact, could help the Earth's magnetic field to maintain its power.
This asymmetry could also have to do with the reversal of the magnetic poles, a phenomenon for which there is still no unique explanation. As the Berkeley research team admits, "the question is always: does it have anything to do with Earth's pole reversal?"