Without Earth's magnetic field, life on the planet might not exist.
For 3.4 billion years, this magnetic field has prevented Earth from becoming extremely vulnerable to high-energy particles called cosmic radiation.
Scientists know that what generates the protective magnetic field is the low heat conduction of liquid iron in the planet's outer core. This phenomenon is known as "geodynamo."
However, although geodynamo has been identified, experts have yet to understand how it was first created and sustained all throughout history.
Now, a new study by scientists from the German Electron Synchrotron or DESY may finally shed light on the timeline of this incredible occurrence.
Additionally, the new report may even solve a puzzle raised in 2012 called "geodynamo paradox," researchers said.
Geodynamo Paradox
Earth was formed from rocky materials that surrounded the Sun during its early years. Over time, iron — the densest material — sank within and created the core, mantle and crust.
The planet's inner core is made up of solid iron with some other materials dragged along the layering process. Its temperature is estimated to be at 5,400 degrees Celsius (9,800 degrees Fahrenheit).
On the other hand, the outer core is made up of liquid iron alloy. Its motion gives rise to the magnetic field.
Here's how it all works: geodynamo is fed by convection — heat transfer by mass motion of fluid — that stirs the outer core's liquid iron, electrically conducting the material. Think of boiling water in a pot.
Add this phenomenon to the rotation of Earth and a dynamo effect sets in. A geomagnetic field is then formed.
The strength of convection in the outer core relies on heat transferred from the core to the lower mantle, as well as on the thermal conductivity of iron in the outer core. This means that heat from the inner core is transferred to the outer core through conduction, causing it to melt into liquid magma.
Past studies have postulated that iron's thermal conductivity in the core was at 150 watts per meter per kelvin, but such a high amount would prevent the geodynamo from even starting up. If a lot of heat were transferred through conduction, not much energy would be left to power convection and the geodynamo.
This amount would also mean that the geodynamo effect was only supported rather recently in Earth's history — only about a billion years or so. However, calculations can trace back the phenomenon to at least 3.4 billion years. This was the geodynamo paradox.
Finding Answers
This prompted DESY scientists to conduct a direct measurement of the thermal conductivity of iron. Because they couldn't take samples from the core, they placed iron under temperatures and pressures that match the core's conditions. Their goal was to determine the energy budget of the core to power the dynamo.
Led by Alexander Goncharov, scientists used a laser-heated diamond anvil cell to copy planetary core conditions and investigate how iron conducts heat under these situations.
The diamond anvil cell works by squeezing tiny samples of material between two diamonds, which recreates the pressures of the deep earth. The laser heats material to the proper core temperatures.
Goncharov and his team were able to look at samples of iron under pressures and temperatures that would be found inside planets with different sizes, from Mercury to Earth.
In the end, researchers found that the ability of iron to transmit heat were not at par with previous estimates of thermal conductivity in the core. It was actually between 18 and 44 watts per meter per kelvin.
This suggests that the energy needed to sustain the geodynamo has been present since very early in Earth's history, researchers concluded.
"Our results strongly contradict the theoretical calculations," says Zuzana Konôpková, one of the researchers of the study.
The details of the research are featured in the journal Nature.
