Exploring the mysteries of the Earth's "heart"

The Earth's dense iron core may rotate more slowly than the rest of the Earth. Image source: British "New Scientist" website

Science and Technology Daily reporter Zhang Jiaxin

What lies deep within the land under our feet?

In fact, humans know even less about the interior of the Earth than we do about the vast universe. If you travel from the surface of the Earth to the center of the Earth, the journey is about 6,500 kilometers. Although this is the same distance from Boston, USA to Helsinki, Finland, it is much more difficult to cross. If "going straight down" is the direction to explore the center of the Earth, then humans have actually only walked 12 kilometers in this direction, or only 0.2% of the distance. The hole drilled to this depth is the famous Kola Borehole in Russia.

Now, scientists are thinking about using other methods and data to understand the Earth below our feet, and then matching that information with the models they have developed for the Earth's interior.

Perhaps the most important data one can gather about Earth's interior is how quickly seismic waves from earthquakes travel through the planet. The waves move at different speeds depending on which layers they intersect. Using this data, scientists are gaining new insights into Earth's "inner heart."

Russian nesting dolls? Iron balls found in the innermost part of the Earth's core

Traditional cross-section diagrams of the Earth show that its interior is divided into four layers: crust, mantle, outer core and inner core. But now, geography textbooks may have to be rewritten again.

According to an earth science study published in the British journal Nature Communications on February 21, new understanding has been put forward on the question of whether the Earth has an innermost core: the Russian doll structure on Earth has an unknown fifth layer - the "innermost core."

Researchers pointed out that the Earth's inner core may be an iron ball with a radius of about 650 kilometers. It and its outer shell are composed of iron-nickel alloy, as well as other trace elements.

Scientists from the Australian National University's School of Earth Sciences combed through data from current detectors and measured the different arrival times of seismic energy waves generated by earthquakes as they propagated through the Earth's interior. For the first time, they observed these waves traveling back and forth up to five times along the entire diameter of the Earth. These waves revealed a different existence than previously known, with a radius of about 650 kilometers and separated from the outer layer of the inner core. The researchers believe that its inner interface may reflect that the growth of the inner core has undergone rapid changes.

Is the Earth's core no longer spinning? The mystery of the slowdown remains to be solved

A study published in Nature Geoscience this year has attracted widespread attention and was even promoted by some media as "The Earth's core has stopped rotating!" This does sound very "dramatic" and makes it seem that our planet is about to "derail", but this is not the case. It is just helping people understand the dynamic nature of the Earth's core.

The Peking University study used repeated seismic wave propagation paths to infer the movement of the Earth's inner core. The researchers found that around 2009, the Earth's inner core slowed down its rotation speed for a period of time, rotating in sync with the Earth's surface - and now the speed of the Earth's inner core has lagged behind the speed of the Earth's surface.

When the researchers looked at the data, they found that the same thing seemed to happen in the early 1970s. This likely indicates that the Earth's inner core has a 70-year cycle of speeding up and slowing down, oscillating back and forth. This change shows up as a small change (a fraction of a second) in the length of a day (the Earth's rotation). So in a sense, the inner core is "oscillating" rather than "rotating."

Is the mantle melting? New findings from asthenosphere research

Below the crust is the mantle. Together with the top of the upper mantle, the crust makes up the lithosphere. Below the lithosphere is the asthenosphere, which is solid but ductile; it bends and flows. Convection occurs in the mantle as hot rock rises from deep within the Earth to the surface. Some of the hot rock melts beneath mid-ocean ridges and other tectonic boundaries. Where molten rock (magma) is present, seismic waves tend to slow down as they travel through the "liquid."

According to another study published in the journal Nature Geoscience on February 6, a research team led by the University of Texas at Austin used seismic data to examine the state of the mantle and discovered a new layer of partially molten rock beneath the crust, which is expected to provide new ideas for explaining the movement of the Earth's plates.

The researchers found that this rock layer lies about 150 kilometers below the surface and is part of the asthenosphere.

Some headlines have used phrases like "lava layer" or "lurking hidden lava layer," but that's not entirely the case, Discover magazine reported. The layer proposed in the study is partially molten, meaning it's likely mostly solid but with some significant magma scattered around. The researchers didn't say how much, but perhaps 20% of the layer is liquid rock.