(ORDO NEWS) — The earth formed about 4.5 billion years ago. Since then, the bowels have been slowly cooling down.
While surface and atmospheric temperatures fluctuate over millennia (and yes, those outside temperatures are currently rising), the molten interior—our planet’s beating heart—is cooling all the time.
This is not a metaphor. A spinning, convective dynamo deep inside the Earth creates a huge magnetic field, an invisible structure that scientists say protects our world and allows life to flourish. In addition, mantle convection, tectonic activity, and volcanism are thought to help sustain life by stabilizing global temperatures and the carbon cycle.
Since the Earth’s interior is still cooling and will continue to cool, this means it will eventually solidify and geological activity will cease, possibly turning the Earth into bare rock like Mars or Mercury. A new study has shown that this could happen sooner than previously thought.
The key could be a mineral at the boundary between the Earth’s outer iron-nickel core and the molten liquid lower mantle above it. This boundary mineral is called bridgmanite, and how fast it conducts heat will determine how quickly heat seeps through the core into the mantle.
Determining this rate is not as easy as testing the conductivity of bridgmanite under ambient atmospheric conditions. Thermal conductivity can vary with pressure and temperature, which vary greatly in the depths of our planet.
To overcome this difficulty, a team of scientists led by planetary scientist Motohiko Murakami of ETH Zurich in Switzerland irradiated a Bridgmanite single crystal with pulsed lasers, simultaneously increasing its temperature to 2440 Kelvin and pressure to 80 GPa, which is close to conditions in the lower mantle to 2630 Kelvin and 127 GPa. pressure.
“This measurement system allowed us to show that the thermal conductivity of bridgmanite is about 1.5 times higher than expected,” Murakami said.
In turn, this means that the flow of heat from the core to the mantle is higher than we thought, and therefore the rate at which the Earth’s interior is cooling is faster than we thought.
And this process can be accelerated. When cooled, bridgmanite transforms into another mineral called postperovskite, which is even more thermally conductive and therefore increases the rate of heat loss from the core to the mantle.
As for exactly how much faster, that’s unknown. The cooling of the entire planet is not something we understand very well. Mars is cooling a little faster because it is significantly smaller than Earth, but there are other factors that could play a role in how quickly the interior of the planet cools.
For example, the decay of radioactive elements can release enough heat to sustain volcanic activity. Such elements are one of the main sources of heat in the Earth’s mantle, but their contribution is not well understood.
“We still don’t know enough about these events to determine their impact,” Murakami said.
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