What’s the News: In geologists’ traditional view of the middle of the Earth, the solid inner core is gradually growing as more of the liquid core freezes, as the planet continues its billions-of-years-long process of cooling off. But now scientists are suggesting that parts of the solid inner core get so hot that they turn liquid, and that this is all linked to what’s happening in the Earth’s crust—meaning that our the earthquakes, volcanoes, and plate tectonics that we see are connected to the very heart of the planet.
How the Heck:
Using computer models and seismology data, the researchers discovered that parts of the mantle can become hot enough that heat is forced back into the core, melting “a small fraction of the inner core’s surface.” They say it’s possible that around 1% of the inner core’s surface is melting, which is roughly 77,000 square miles.
Below the Pacific Ocean’s seismically active “Ring of Fire,” for example, heat is expelled from Earth’s interior via volcanoes and cold crustal plates get thrust into the mantle, all “drawing a lot of heat from the core, helping it freeze.” But underneath regions in Africa and the Pacific that are far away from any of these heat-expelling processes, models show that the mantle can get so hot that it begins melting the inner core. It suggests “that the whole dynamics of the Earth’s core are in some way linked to plate tectonics, which isn’t at all obvious from surface observations,” says co-author Jon Mound.
What’s the Context:
Overall, Earth’s core has been cooling for billions of years, causing the liquid outer core to slowly solidify and increase the size of the solid inner core. Scientists estimate that the solid inner core’s diameter grows by roughly 1 millimeter each year.
The heat expelled from the core rises up through the mantle and creates convection currents. It’s this convection and Earth’s spin that help create our magnetic field.
In the past, researchers have noted that seismic waves travel at different speeds as they pass through the some parts of the inner core. So this study suggests that the localized melting of the inner core may be the reason, since waves would travel slower in the melted parts and faster in the solid parts.
In order to determine for sure if the inner core is actually melting, researchers “would need larger arrays of seismometers spread more evenly around the world, particularly in the oceans, which is a technological hurdle,” according to Mound.
Not So Fast: Not all of the researchers’ models indicated melting in the inner core, so it still “may not be possible to get the core flow we need to induce melting.” The reason for this uncertainty, according to Mound, is that “there is the general problem that all computer models of the dynamics of the Earth’s core can’t actually capture the true dynamics, as nobody has sufficient computer power to run models with enough detail.”
Reference: David Gubbins, Binod Sreenivasan, Jon Mound, Sebastian Rost. “Melting of the Earth’s inner core.” Nature, 2011; 473 (7347): 361 DOI: 10.1038/nature10068
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