The magnetic field guarantees life on our planet: what made it work for billions of years? Perhaps a feature of the Earth's core that was not thought of. Illustration: plumes of the Earth's magnetic field | Jurik Peter / Shutterstock One of the characteristics of our Planet is its magnetic ...
The magnetic field guarantees life on our planet: what made it work for billions of years? Perhaps a feature of the Earth's core that was not thought of.
Illustration: plumes of the Earth's magnetic field
| Jurik Peter / Shutterstock
One of the characteristics of our Planet is its magnetic field, neither too weak nor too intense: just what is needed to protect the surface of the Earth from charged particles of the solar wind and cosmic radiation. If the magnetic field were not there, life, as it appeared, would disappear in a short time. Today we know that this shield is produced by the motions of liquid iron, the most abundant element in the outer core of the Earth, which gives life to a geodynamo: a planetary dynamo which, originating an electric current, causes the appearance of a magnetic field as a consequence ... This description is a simplification, however, and hides questions for which geologists still have no answers.
However, an international study (published in Nature Communications) could make us take a step forward in understanding the mechanism of the geodynamo: for the team, it would be the presence of elements lighter than iron in the Earth's core to allow the geodynamo, in the present as in the past. .
The structure of the Earth and the motions of the mantle
The structure of the Earth and the motions of the mantle, highlighted by the arrows. The arrows indicate the direction of motion of the mantle, which cools near the crust and partly exits the oceanic ridges and partly returns to the depths. The movement raises and lowers the oceanic crust by up to 2 kilometers. For further information: The paradox of the Earth's core. |
Our Planet was formed from the accumulation of dust and gases that surrounded the protostar that would give rise to the Sun: in those early stages the heavier elements - such as iron - aggregated towards the center of what would become a planet, while the lighter ones were distributed and differentiated towards the outside, towards what would become the surface.
This is why the Earth today has a chemical diversification passing from the crust to the mantle and up to the core, but there are no homogeneous zones: while the iron sank to form the core, it also dragged with it a part of light elements - such as oxygen, sulfur, carbon, hydrogen ... - whose presence is confirmed by seismographs that measure the way in which the seismic waves of mega earthquakes cross the planet.
Little importance has been given to these elements in relation to the functioning of the geodynamo, powered, as has always been thought, exclusively by the heat of the inner core. According to this hypothesis, the energy emitted by the inner core is sufficient to keep the liquid iron of the outer core in motion, which thus generates the magnetic field.
The new study wants to add a piece to this scenario: it hypothesizes that the lighter elements present in the outer core lower the threshold of the temperature necessary to keep liquid iron in motion, and that, without these elements, perhaps it would never have triggered the geodynamic effect, even with the same heat. The models used for the study have highlighted a scenario in which 8% of silica in the outer core would be sufficient to have the geodynamo in operation from the beginning of the planet's history to today. There are still no projections or models on the role of the other light elements, and this is what the next studies will focus on.
