Beneath Africa and the Pacific Ocean, directly above the core–mantle boundary, seismologists have been detecting for decades two strange continent-sized structures. These are the so-called LLSVPs (Large Low Shear Velocity Provinces), regions where shear wave velocity is 3–5 percent lower than normal, along with adjacent ultralow-velocity zones (ULVZs), which are thin molten patches. These structures did not fit into any classical model of Earth’s evolution and were long considered one of the major geological mysteries of the twenty-first century.
A New Hypothesis: They Are Remnants of a Global Magma Ocean
A research team led by Yoshinori Miyazaki of Rutgers University published a study in Nature Geoscience that appears to finally explain their origin. According to the group’s calculations, in its first few hundred million years Earth was indeed covered by a continuous ocean of molten magma. As it cooled, this ocean should have separated into clearly defined chemical layers, but this separation never occurred. The researchers argued that the reason was the Earth’s core.
The Core “Contaminated” the Mantle
Modelling showed that over billions of years silicon, magnesium, and other elements slowly seeped from the core into the lower mantle. This continuous mixing prevented the magma from crystallizing evenly and turned the base of the mantle into a chemically heterogeneous mixture. These very heterogeneities eventually solidified into the modern LLSVPs and ULVZs, preserved as ancient scars left by the interaction between the core and the primordial magma ocean.
Why This Matters for the Entire Planet
Miyazaki stated that the discovery extends far beyond deep Earth geology. The way the core exchanged material with the mantle determined how rapidly Earth cooled, how mantle plumes and volcanism operated, and how the atmosphere formed and water was retained. These processes made Earth habitable and set it apart from Venus, which became a runaway greenhouse world, and Mars, which froze and lost much of its atmosphere.
The researcher emphasized that what happens at the core–mantle boundary may hold the key to understanding why, among the three sibling planets, only one became a home for life.
Summary
The giant anomalies deep inside Earth are not random structures but the solidified remnants of a global magma ocean that was altered by elements seeping from the planet’s core over billions of years. The new study explains their origin and brings scientists closer to answering why Earth, out of all the planets in the Solar System, ultimately became suitable for life.
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