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What goes down in the center of our planet is largely a mystery, and also what goes up.
The truth is that no human has ever passed through the crust, or has dug deep enough to penetrate Earth’s rocky mantle, let alone its liquid iron core, so we don’t know what kind of interactions take place here. And that’s not for lack of trying.
Sitting at a depth of approximately 2,900 kilometers (1,800 miles), the core of our planet lies far beyond our technological reach, at least for now, and yet, through educated guesswork and intelligent theoretical models, scientists have opened a window to some of the riddles below our feet.
New research now suggests that Earth’s molten core may be leaking iron in the upper mantle, which is more than a thousand degrees cooler than the liquid core.
For decades, scientists have debated whether the core and the mantle exchange physical material.
Earth’s powerful magnetic field and its electrical currents certainly imply that there is a lot of iron in the core. Additionally, samples of mantle rock brought to the surface also show a significant chunk of iron, leading some to speculate that the material comes from the core.
To get an idea of whether this might be possible, the researchers have turned to laboratory experiments showing how iron isotopes move between areas of different temperatures under high pressure and temperature.
(L. O’Dwyer Brown, University of Aarhus)
Using this information to create a model, the team’s results suggest that heavy iron isotopes may be migrating from Earth’s hot core to the cooler mantle. Whereas the light isotopes of iron would do the opposite and go from cold to hot back to the nucleus.
These results are still theoretical, but they could teach us something important about how the interior of our planet works.
“If correct, this means improving our understanding of the core-mantle interaction,” says geologist and petrologist Charles Lesher of Aarhus University in Denmark.
And that kind of knowledge is really important. It can help us interpret seismic images in the deep mantle and allow us to model how chemicals and heat rise and fall between Earth’s layers.
Using computer simulations, the authors were even able to show how this core material can reach the Earth’s surface, with heavier isotopes that essentially hook into wells of a warm mantle plume, such as those found in Samoa. and Hawaii. a possible signature of the leaky core from Earth.
A study published last year suggested something similar. Its authors found that the core material, in this case, the tungsten isotopes, were also transferred to the surface through rising mantle feathers and that the core has likely been filtering this material for the past 2.5 billion years.
Lesher says his results also suggest that iron isotopes from the nucleus have leaked into the mantle for billions of years. But if exchanges like this are really happening, the question is: What is the long-term impact?
At this time, no one really knows. The new simulation only shows that a core-to-mantle leak is possible at high temperature and pressure, and could explain why rocks in the mantle hold much more iron than meteorites – in short, iron fluid comes from the heart.
The authors admit that there is considerable uncertainty in some of the parameters of their model, such as diffusion, thermal conductivity, or the amount of central liquid that actually infiltrates the mantle. The chosen numbers may not represent the reality of the situation.
However, the exchange of iron isotopes through the core-mantle barrier by thermal diffusion seems more than capable of ironing our mantle, so to speak.
“This does not exclude other processes, but simply shows that thermodiffusion is a plausible isotopic fractionation agent in the region of [core-mantle-barrier] on geological time scales, “the authors conclude.
The study was published in Nature Geoscience.
