The Earth’s Core: An Enigma 1,800 Miles Below Our Feet

Geologists have long known that Earth’s core, some 1,800 miles beneath our feet, is a dense, chemically doped ball of iron roughly the size of Mars and every bit as alien. 

It’s a place where pressures bear down with the weight of 3.5 million atmospheres, like 3.5 million skies falling at once on your head, and where temperatures reach 10,000 degrees Fahrenheit — as hot as the surface of the Sun. 

It’s a place where the term “ironclad agreement” has no meaning, since iron can’t even agree with itself on what form to take. It’s a fluid, it’s a solid, it’s twisting and spiraling like liquid confetti.

Researchers have also known that Earth’s inner Martian makes its outer portions look and feel like home. The core’s heat helps animate the giant jigsaw puzzle of tectonic plates floating far above it, to build up mountains and gouge out seabeds. 

At the same time, the jostling of core iron generates Earth’ magnetic field, which blocks dangerous cosmic radiation, guides terrestrial wanderers and brightens northern skies with scarves of auroral lights.

Now it turns out that existing models of the core, for all their drama, may not be dramatic enough. Reporting recently in the journal Nature, Dario Alfè of University College London and his colleagues presented evidence that iron in the outer layers of the core is frittering away heat through the wasteful process called conduction at two to three times the rate of previous estimates. 

The theoretical consequences of this discrepancy are far-reaching. The scientists say something else must be going on in Earth’s depths to account for the missing thermal energy in their calculations. 

They and others offer these possibilities:

• The core holds a much bigger stash of radioactive material than anyone had suspected, and its decay is giving off heat.
• The iron of the innermost core is solidifying at a startlingly fast clip and releasing the latent heat of crystallization in the process.
• The chemical interactions among the iron alloys of the core and the rocky silicates of the overlying mantle are much fiercer and more energetic than previously believed.
• Or something novel and bizarre is going on, as yet undetermined.

“From what I can tell, people are excited” by the report, Dr. Alfè said. “They see there might be a new mechanism going on they didn’t think about before.”

Researchers elsewhere have discovered a host of other anomalies and surprises. They’ve found indications that the inner core is rotating slightly faster than the rest of the planet, although geologists disagree on the size of that rotational difference and on how, exactly, the core manages to resist being gravitationally locked to the surrounding mantle.

Miaki Ishii and her colleagues at Harvard have proposed that the core is more of a Matryoshka doll than standard two-part renderings would have it. 

Not only is there an outer core of liquid iron encircling a Moon-size inner core of solidified iron, Dr. Ishii said, but seismic data indicate that nested within the inner core is another distinct layer they call the innermost core: a structure some 375 miles in diameter that may well be almost pure iron, with other elements squeezed out. 

Against this giant jewel even Jules Verne’s middle-Earth mastodons and ichthyosaurs would be pretty thin gruel.

Core researchers acknowledge that their elusive subject can be challenging, and they might be tempted to throw tantrums save for the fact that the Earth does it for them. Most of what is known about the core comes from studying seismic waves generated by earthquakes.

As John Vidale of the University of Washington explained, most earthquakes originate in the upper 30 miles of the globe (as do many volcanoes), and no seismic source has been detected below 500 miles. But the quakes’ energy waves radiate across the planet, detectably passing through the core.

Granted, some temblors are more revealing than others. “I prefer deep earthquakes when I’m doing a study,” Dr. Ishii said. “The waves from deep earthquakes are typically sharper and cleaner.”

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