Geoscientists studying the Earth’s mantle have stumbled upon a surprising enigma beneath the Pacific Ocean. Using seismic waves generated by earthquakes, researchers identified anomalies—regions where waves behave unexpectedly, suggesting the presence of structures colder or compositionally different from the surrounding molten rock. These findings pose significant questions about the hidden dynamics of our planet.
A Geological Puzzle Under the Pacific Plate
Typically, such anomalies might be linked to tectonic plates sinking into the mantle at subduction zones. However, this explanation falters beneath the Pacific Ocean, as the region consists of a single, massive plate with no subduction activity. The nature and origin of these deep-seated structures remain an open question.
According to Thomas Schouten, a doctoral student at the Geological Institute of ETH Zurich and lead author of the study, “With the new high-resolution model, we can see such anomalies everywhere in the Earth’s mantle. But we don’t know exactly what they are or what material is creating the patterns we have uncovered.”
The presence of cold zones scattered throughout the mantle hints that these structures may have formed at various times from diverse sources. They could even predate the last 200 million years of plate tectonic activity.
Tracing Ancient Earth Materials
One hypothesis posits that these anomalies are remnants of silica-rich material dating back 4 billion years, possibly surviving despite the mantle’s convective currents. Another theory suggests that iron-rich rocks could have accumulated over billions of years due to mantle movements.
Schouten elaborates, “We think that the anomalies in the lower mantle have a variety of origins. It could be either ancient, silica-rich material that has been there since the formation of the mantle, or zones where iron-rich rocks accumulate as a consequence of these mantle movements over billions of years.”
Challenges in Peering Beneath the Surface
The study’s limitations stem from relying solely on seismic wave velocities to infer the mantle’s composition. Although advanced models offer insights, the inability to physically access the mantle leaves much to interpretation. As Schouten points out, “We have to calculate the different material parameters that could generate the observed speeds of the different wave types. Essentially, we have to dive deeper into the material properties behind the wave speed.”
The findings, which shed light on the complex and still-mysterious inner workings of our planet, were published in Scientific Reports. Further research is essential to unravel the secrets buried deep beneath the Earth’s crust.
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