The interior of planet Earth has a core that has remained hot for over 4.5 billion years but is slowly and inevitably cooling.
The Earth’s core is key to life. If one day it goes out, the planet will become a gigantic, cold and inert rock. Now recent research has calculated that this cooling is occurring faster than previously thought.
This cooling occurs on scales of billions of years, so no matter how fast it occurs, none of us will be alive to see what this cold death of the planet would look like.
Experts, however, agree that investigating these natural processes is key to better understanding Earth’s evolution and the phenomena that affect life on the planet.
But what does this cooling consist of, and how did they discover that it is happening faster than previously thought?
the interior of the earth
The Earth’s core lies almost 3,000 km deep in the Earth’s crust, with a radius of 3,500 km. Core temperatures can fluctuate between 4,400°C and 6,000°C, temperatures similar to those of the Sun.
The inner core is a solid sphere, composed mostly of iron. The outer core is formed by a malleable liquid, composed of iron and nickel. It is in the outer core that the Earth’s magnetic field is formed, which protects the planet from dangerous solar winds. The colossal amount of thermal energy that emanates from the interior of the planet sets in motion phenomena such as tectonic plates and volcanic activity.
In addition, at the boundaries of the core a process takes place that was crucial to the new study: Earth’s mantle convection, which refers to the transfer of heat from the core to the mantle.
the core border
Scientists don’t know exactly how long it will take for the Earth to cool to the point where the natural phenomena that drive the core stop occurring or the magnetic field disappears, for example.
A team from the Swiss Federal Institute of Technology Zurich (ETH) and the Carnegie Institution for Science in the United States believe that the key to unlocking this mystery lies in the minerals that transport heat from the core to the mantle.
This border region is mainly made up of a mineral called bridgmanite, which has a crystalline structure and can only exist under great pressure, from about 700 km deep.
There is no technology to excavate and study minerals at this depth, so ETH professor Motohiko Murakami designed an experiment to simulate these conditions in the laboratory.
pressure and temperature
Murakami and his colleagues developed a method to measure how much heat bridgmanite can conduct. What they did was make a bridgmanite diamond from the elements that make up this mineral.
They then inserted the crystal into a device that simulates the pressure and temperature that prevail inside the Earth. Inside the device, they fired pulses of laser beams that radiated and heated the mineral, in a process known as “optical absorption measurement”.
In this way, they could see how the mineral reacted at different pressures and temperatures. “This measurement system allowed us to show that the thermal conductivity of bridgmanite is about 1.5 times higher than previously assumed,” says Murakami in a statement.
According to the researcher, this indicates that the heat flux from the core to the mantle is also greater than previously thought.
The result of the experiment suggests that the faster heat is transferred from the core to the mantle, the faster heat is lost from the core, which accelerates the Earth’s cooling.
Furthermore, the authors believe that this cooling would change the composition of mantle minerals.
When bridgmanite cools, it turns into another mineral called post-perovskite.
Post-perovskite conducts heat much more efficiently than bridgmanite, so as bridgmanite at the mantle boundary converts to post-perovskite, Earth cools even faster, the researchers say.
Destined to die?
This faster cooling could have several consequences, the study authors note. On the one hand, it can cause tectonic plates, which are kept in motion by mantle flow, to decelerate faster than expected.
“Our results can give us a new perspective on the evolution of Earth’s dynamics,” explains Murakami.
Murakami, however, cautions that, at this point, they cannot estimate how long it will take for this cooling to stop activity in the mantle.
For this, they need to better understand the dynamics of the mantle and the reactions of the elements that compose it.
“This study offers new insight into the main geological process that affects rocky planets (like Earth): the speed at which they cool,” Paul Byrne, professor of Planetary and Land from Washington University in Saint Louis, United States, who was not involved in the research.
“Mars, Mercury and the Moon have cooled so much in the last 4.5 billion years that, geologically speaking, they are essentially inert.”
Therefore, unlike Earth, Mars, Mercury and the Moon do not have tectonic plates, explains the expert. “Is this the fate that awaits our world?” Byrne wonders.
Source: Folha
