Earth formed 4.5 billion years ago or so, and since then, heat has been slowly cooling from within.
As surface and atmospheric temperatures fluctuate over eons, the molten interior — the beating heart of our planet — has been cooling all this time.
And that’s not a simple metaphor: a rotating dynamo and convection deep within the Earth is what generates its vast magnetic field, an invisible structure that scientists believe protects our world and allows life to thrive. In addition, mantle convection, tectonic activity, and volcanic activity are thought to help sustain life by stabilizing global temperatures and the carbon cycle.
Since the Earth’s interior is still cold, and will continue to do so, this means that the interior will eventually solidify, geological activity will cease, and possibly turn Earth into a barren rock, similar to Mars or Mercury. And new research has revealed that this may happen sooner than previously thought.
The key could be metal on the boundary between Earth’s outer core of iron-nickel and the lower molten liquid from the mantle above it. This boundary mineral is called bridgmanite, and how quickly it conducts heat will affect how quickly heat escapes through the core and out into the mantle. Determining this rate is not straightforward, and thermal conductivity can vary based on 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 single crystal of bridgmanite with pulsed lasers, simultaneously increasing its temperature to 2,440 K and pressure to 80 gigapascals, which is close to We know it for conditions in the lower mantle – up to 2,630 K and 127 gigapascals of pressure.
“This measurement system allows us to show that the thermal conductivity of bridgemanite is about 1.5 times higher than assumed,” Murakami said.
This, in turn, means that the heat flow from the core into the mantle is higher than we thought – and thus, the rate of cooling of the Earth’s interior is faster.
The process can be accelerated. When it cools, bridgemanite turns into another mineral called post-perovskite, which is more heat conductive and thus increases the rate of heat loss from the core to the mantle.
“Our results can give us a new perspective on the evolution of Earth dynamics,” Murakami said. “It is suggested that Earth, like the other rocky planets Mercury and Mars, is cooling and becoming inactive much faster than expected.”
As for exactly how fast, that is not known, as cooling an entire planet is not something we understand very well. Mars cools a little faster because it is much smaller than Earth, but other factors may play a role in how quickly the inner planets cool.
For example, the decay of radioactive elements can generate enough heat to maintain volcanic activity. These 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 types of events to determine their timing,” Murakami said.
However, it likely won’t be a quick process on human scales, either way. In fact, Earth could have become uninhabitable by other mechanisms long before then. So we might have some time to work more on the problem to find out.
The team’s research was published in Messages Earth and Planetary Sciences.
Source: Science Alert