Planetary warning! Something ‘big’ is moving inside Earth; here’s what scientists just found |

Something ‘big’ is moving inside Earth; here’s what scientists just found For decades, scientists have sought to unravel the mysteries hidden deep beneath Earth’s surface. One of the most puzzling regions has been the D” layer, located about 2,700 kilometres (1,700 miles) beneath the surface, at the boundary between the planet’s lower mantle and outer core. This zone has long been known for its unusual seismic properties, which have sparked debates about its composition and behaviour.Now, a groundbreaking study conducted by researchers at ETH Zurich has revealed that solid rock in this deep layer of Earth’s mantle can move like a fluid, while still maintaining its solid state. Led by Professor Motohiko Murakami, the research team has provided experimental evidence explaining how minerals in the D” layer align and deform over geological timescales. The findings, published in Communications Earth & Environment, shed new light on mantle convection, plate tectonics, volcanic activity, and even the generation of Earth’s magnetic field.

Earth’s hidden D” layer finally comes into focus

The D” layer sits just above the outer core and plays a key role in the planet’s internal dynamics. It has been a focal point for geoscientists because seismic waves passing through it behave differently than expected, often travelling faster in some regions and slower in others. Understanding the cause of these variations has been a challenge, as conditions in this layer involve extreme pressures and temperatures that are difficult to replicate in laboratory experiments.To study the D” layer, Murakami’s team used diamond anvil cells—devices capable of generating pressures exceeding those found deep within Earth—and X-ray diffraction techniques to examine the atomic structure of minerals under such conditions.The researchers recreated the high-pressure, high-temperature environment of the D” layer and observed how minerals behaved. They used magnesium germanate crystals as an experimental analogue for mantle minerals because they exhibit similar structural properties but are easier to work with in the lab.

Role of post-perovskite in mantle dynamics

The study focused on post-perovskite, a high-pressure phase of the mineral perovskite that forms under the extreme conditions of the D” layer. Post-perovskite has unique structural properties that allow its crystals to align in specific patterns when subjected to geological stress over long periods.This alignment enables solid-state flow, a process in which solid rock deforms and moves like a viscous fluid without melting. Such movement plays a critical role in mantle convection—the slow circulation of rock that drives the movement of tectonic plates at Earth’s surface.

Explaining seismic wave anomalies

One of the major outcomes of the research is the explanation for why seismic waves can accelerate by up to seven percent when passing through certain regions of the D” layer. The alignment of post-perovskite crystals changes the way seismic energy travels through the rock, matching patterns observed in global seismological data.This discovery effectively resolves a long-standing puzzle in geophysics and provides a clear link between deep mantle mineral behaviour and surface-level seismic measurements.

Impact on plate tectonics and volcanism

The movement of solid rock in the D” layer has significant implications for plate tectonics. Mantle plumes—columns of hot rock rising from deep within the Earth—can be guided by the alignment of post-perovskite minerals, directing heat and material toward the upper mantle and crust.These processes are responsible for creating volcanic hotspots such as those in Hawaii and Iceland. The study also helps explain how deep mantle processes influence the formation of mountain ranges and the activity along subduction zones where one tectonic plate slides beneath another.

Connection to Earth’s magnetic field

Beyond plate tectonics, the findings have important implications for understanding the geodynamo—the mechanism that generates Earth’s magnetic field. The distribution of heat from the deep mantle to the outer core affects convection within the liquid iron core, which in turn influences magnetic field generation.By showing how the D” layer channels heat through solid-state flow, the study reveals a previously underappreciated link between deep mantle processes and the stability and variations of Earth’s magnetic field over the past 200 million years.

Methodology and experimental insights

Murakami’s team achieved their results by:

• Using diamond anvil cells to create pressures of hundreds of gigapascals, similar to those at the core-mantle boundary.
• Applying high-temperature lasers to simulate the intense heat found deep underground.
• Analysing the crystal structures with synchrotron X-ray diffraction to observe how minerals deform under such conditions.
• Studying magnesium germanate as a stand-in for mantle perovskite allows the researchers to observe mineral alignment and flow properties.

Significance for Earth science

The discovery that solid rock can behave like a fluid deep within the Earth provides:

• A more complete model of mantle convection and its effects on surface geology.
• An explanation for seismic anomalies detected in the D” layer.
• New insights into the heat flow between Earth’s core and mantle.
• A better understanding of how mantle plumes form and influence volcanism.
• A link between deep Earth processes and magnetic field generation.

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