New insights into a pair of colossal, continent-sized structures 1,800 miles beneath the Earth’s surface are revealing clues into how the planet formed and evolved, as well as the formation of life on Earth.
The mysterious deep-Earth structures, which have long baffled scientists and are so anomalous that they defy traditional models, may now have a fascinating explanation, although questions linger about exactly what processes led to their formation.
The findings, published in Nature Geoscience, were the result of work led by Yoshinori Miyazaki, a geodynamicist at Rutgers University, working along with a team of collaborators.
Anomalies at the Boundary
1,800 miles beneath the Earth’s surface, massive structures exist that have long been recognized by geologists. These unusual formations exist at the point where Earth’s Mantle and its outer core converge, and are composed of massive accumulations of extremely hot, dense rock that are comparable in size to Earth’s present-day continents.
The structures come in two types, which are known as large low-shear-velocity provinces and ultra-low-velocity zones. The former are structures that are found deep beneath the Pacific Ocean and the African continent, and are comprised of large, dense accumulations of very hot rock. Their counterpart—ultra-low-velocity zones, by contrast, are large molten areas which resemble “puddles” of lava situated around the Earth’s core.
Each of these structures appears to possess odd structural traits based on their composition, which includes the fact that they both can slow the progress of seismic waves passing through inner-Earth regions.
However, the presence of these features is far from being coincidental, according to Miyazaki.
“These are not random oddities,” the researcher said in a recent statement, instead likening the unusual structures to the “fingerprints of Earth’s earliest history.”
Understanding why these inner-Earth features exist, Miyazaki says, could ultimately help geologists unravel the mystery of not just how the early planet formed but also what processes may have contributed to it becoming habitable over time.
Exploring an Ancient Ocean of Magma
Miyazaki is uniquely positioned to unravel such questions. As an assistant professor in Rutgers’ Department of Earth and Planetary Sciences in the university’s School of Arts and Sciences, Miyazaki is a theoretical planetary scientist whose work focuses on unraveling the origin and early evolution of planets like Earth by using mathematical models.
If we travel billions of years back in time, our planet was once encased in an ocean of hot molten lava. Gradually over time, it began to cool and take shape into the modern surface and subsurface regions, which researchers expected to resemble a layered shell marked by several distinctive chemical layers.
That wasn’t the case, however. Rather than distinctive layers, scientists were surprised to discover the presence of anomalous large-low shear velocity provinces and ultra-low velocity zones, which, instead of ordered layers, take shape as uneven “blobs” at the lower levels of the planet’s mantle.
That discovery, while seemingly contradictory, was the launchpad for Miyazaki and his collaborators’ research.
“If we start from the magma ocean and do the calculations, we don’t get what we see in Earth’s mantle today,” Miyazaki said.
“Something was missing.”
Missing Pieces of an Ancient Earth Mystery
In searching for the answers to this geological mystery, Miyazaki and his colleagues concluded that the resolution might be hidden in plain sight: that the Earth’s core was itself the seemingly missing component.
Over the course of billions of years, elements that include magnesium and silicon would gradually make their way from the core into the Earth’s mantle, which over time prevented the strong layering of chemicals scientists originally expected.
This not only explains the absence of distinctive layers within the Earth but also the unusual structures at the boundary between the core and the mantle, which are effectively solid portions that were left behind from the lower portions of the original magma ocean, which over time became contaminated through interactions with material from the Earth’s core.
Going beyond simply resolving the mystery of the anomalous structures themselves, Miyazaki says that the discovery could also point to new clues about how the Earth evolved as it cooled, which could lend itself to understanding how life began to emerge.
Additionally, the results offer clues about the reasons for fundamental differences between the atmospheres of Earth and neighboring planets like Venus and Mars.
“Venus’ atmosphere is 100 times thicker than Earth’s and is mostly carbon dioxide, and Mars has a very thin atmosphere,” Miyazaki said. “We don’t fully understand why that is.”
“But what happens inside a planet, that is, how it cools, how its layers evolve, could be a big part of the answer,” he adds.
A Multi-Field Approach
Additionally, by combining data from areas that include mineralogy, geophysics, seismology, and other disciplines, the team’s results offer a pathway toward obtaining a far deeper understanding of processes that contributed to how the Earth formed over time.
Jie Deng, one of the study’s collaborators from Princeton University and a co-author of the new study, called the team’s work a “great example of how combining planetary science, geodynamics, and mineral physics can help us solve some of Earth’s oldest mysteries.”
“The idea that the deep mantle could still carry the chemical memory of early core–mantle interactions opens up new ways to understand Earth’s unique evolution,” Deng added.
Fundamentally, the emerging story of planetary evolution that the team’s work is revealing offers researchers like Deng and Miyazaki much greater insights into the mysteries of the ancient Earth.
“This study gives us a little more certainty about how Earth evolved, and why it’s so special,” Miyazaki said.
The team’s new paper, “Deep mantle heterogeneities formed through a basal magma ocean contaminated by core exsolution,” appeared in Nature Geoscience.
Micah Hanks is the Editor-in-Chief and Co-Founder of The Debrief. A longtime reporter on science, defense, and technology with a focus on space and astronomy, he can be reached at micah@thedebrief.org. Follow him on X @MicahHanks, and at micahhanks.com.