Two enormous structures that sit at the border between the Earth’s mantle and its core have puzzled scientists for decades, defying reigning theories of how our planet came to be.
In a new study published in the journal Nature Geoscience, a team of researchers led by Rutgers University geodynamicist Yoshinori Miyazaki has come up with a new explanation for these structures — suggesting, provocatively, that their formation may be closely tied to the evolution of life on Earth.
The continent-sized lumps of dense, hot rock lie almost 1,800 miles beneath the surface under Africa and the Pacific Ocean. They show up in seismic wave readings, indicating major differences in the surrounding composition of rock.
“These are not random oddities,” said Miyazaki in a statement. “They are fingerprints of Earth’s earliest history.”
“If we can understand why they exist, we can understand how our planet formed and why it became habitable,” he added.
Current theories suggest the early Earth formed a mantle billions of years ago from a massive magma ocean, separating more concentrated from less concentrated material over time, not unlike “frozen juice separating into sugary concentrate and watery ice,” per the statement.
But finding evidence to support this theory has proven more difficult than expected. Instead of even layers, we’ve discovered large irregular lumps of “large-low shear velocity provinces,” structures characteristic of the Earth’s lowermost mantle, and “ultra-low velocity zones,” or patches that slow seismic waves down to extremely low velocities.
“That contradiction was the starting point,” Miyazaki explained. “If we start from the magma ocean and do the calculations, we don’t get what we see in Earth’s mantle today. Something was missing.”
Miyazaki and his colleagues modeled the conditions present billions of years ago, finding that a slow trickle of silicon and magnesium leaking from the Earth’s core may have “contaminated” a “basal magma ocean,” stopping it from solidifying in parts and resulting in a strangely lumpy composition.
“What we proposed was that it might be coming from material leaking out from the core,” Miyazaki said. “If you add the core component, it could explain what we see right now.”
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