The Earth's magnetic field protects us from deadly cosmic radiation, and without it, as you know, life could not exist. The movement of liquid iron in the outer core of the planet, the "geodynamo" phenomenon, generates this field. But how it appeared and was then maintained throughout the entire history of the Earth is a mystery to scientists. A new work published in Nature by a group led by Alexander Goncharov of Carnegie University sheds light on the history of this incredibly important geological formation.
Our planet was formed from the solid material that surrounded the Sun in its youth, and over time, the densest material, iron, sank, sank deeper, forming the layers that we know today: the core, the mantle, the crust. Currently, the inner core is solid iron along with other materials that have been tightened during the layering process. The outer core is an alloy of liquid iron, and its movement generates a magnetic field.
A deeper understanding of how heat is conducted in the solid inner core and liquid outer core is needed to piece together the processes that have evolved our planet and its magnetic field - and more importantly, the energy that maintains a constant magnetic field. But these materials apparently only exist under the most extreme conditions: very high temperatures and very high pressures. It turns out that on the surface, their behavior will be completely different.
“We decided that it would be imperative to directly measure the thermal conductivity of core materials under conditions that match those of the core,” says Goncharov. "Because, of course, we cannot get to the core of the Earth and take samples for ourselves."
The scientists used an instrument called a diamond anvil cell to simulate the conditions of the planetary core and study how iron conducts heat under those conditions. The diamond anvil cell compresses tiny samples of material between two diamonds, creating extreme pressure from the depths of the Earth in the laboratory. The laser heats materials to nuclear temperatures.
Using such a "nuclear laboratory", a team of scientists was able to study samples of iron at temperatures and pressures that can be found inside planets ranging in size from Mercury to Earth - pressures ranging from 345,000 to 1.3 million normal atmospheres and from 1300 to 2700 degrees Celsius - and understand how they conduct heat.
It was found that the thermal conductivity of such iron samples corresponds to the lower end of preliminary estimates of the thermal conductivity of the Earth's core - between 18 and 44 watts per meter per degree Kelvin, in the units that scientists use to measure such things. This suggests that the energy required to maintain a geodynamo has always been available from the very beginning of Earth's history.
“To better understand the thermal conductivity of the core, in the future we will study how non-ferrous materials that were drawn into the core along with sinking iron affect thermal processes inside our planet,” says Goncharov.
Promotional video:
ILYA KHEL