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Seismologists peer into Earth's inner core
At the center the Earth is a solid metal ball, a kind of "planet within a planet," whose existence makes life on the surface possible.
Research shows Earth's solid metal sphere is planet within a planet. Photo: University of Utah
How Earth's inner core formed, grew and evolved over time remains a mystery, one that University of Utah-led researchers are seeking to plumb with the help of seismic waves from naturally occurring earthquakes.
While this 2,442-kilometer-diameter sphere comprises less than 1% of the Earth's total volume, its existence is responsible for the planet's magnetic field, without which Earth would be a much different place.
But the inner core is not the homogenous mass that was once assumed by scientists, but rather it's more like a tapestry of different "fabric," according to Guanning Pang, a researcher at Cornell University.
This research harnessed a special dataset generated by a global network of seismic arrays set up to detect nuclear blasts.
In 1996, the United Nations established the Preparatory Commission for the Comprehensive Nuclear-Test-Ban Treaty Organization to ensure compliance with the international treaty that bans such explosions.
Its centerpiece is the International Monitoring System, featuring four systems for detecting explosions using advanced sensing instruments sited all over the world.
While their purpose is to enforce an international ban on nuclear detonations, they have yielded data scientists can use to shed new light on what's going on in Earth's interior, oceans and atmosphere.
These data have facilitated research that illuminated meteor blasts, identified a colony of pygmy blue whales, advanced weather prediction and provided insights into how icebergs form.
While Earth's surface has been thoroughly mapped and characterized, its interior is much harder to study since it cannot be directly accessed.
The best tools for sensing this hidden realm are earthquakes' seismic waves propagating from the planet's thin crust and vibrating through its rocky mantle and metallic core.
"The planet formed from asteroids that were sort of accreting," said University of Utah seismologist Keith Koper.
"They're running into each other and generating a lot of energy. The whole planet, when it’s forming up, is melting. The iron is heavier and you get what we call core formation. The metals sink to the middle, and the liquid rock is outside, and then it essentially freezes over time. The reason all the metals are down there is because they're heavier than the rocks."
Earth's core, which measures about 4,300 miles across, is comprised mostly of iron and some nickel, along with a few other elements. The outer core remains liquid, enveloping the solid inner core. (U.S. National Science Foundation)
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