Scientists discover the secrets of Earth’s core-mantle boundary

Iron-rich mountainous regions (dark red) near the base of the Earth’s mantle influence the rise of plumes that reach the surface and influence volcanic activity. Photo credit: Caltech.

Deep inside our planet, at the core-mantle boundary (CMB), conditions are incredibly harsh – temperatures rise to thousands of degrees Fahrenheit and pressures are millions of times higher than at Earth’s surface.

This extreme environment has puzzled scientists for years, particularly regarding its influence on the surface world in which we live.

Scientists have long used seismic waves created by earthquakes to explore what lies beneath the Earth’s surface.

These waves travel at different speeds depending on the material they pass through, similar to how sound waves in ultrasound provide images of the human body.

Research has shown that the base of the Earth’s mantle is complex and diverse. This was highlighted by the discovery of ultralow velocity zones (ULVZs), areas where seismic waves slow significantly.

These zones, which lie approximately 3,000 kilometers below the surface, are thick, mountain-like regions, but their composition and nature have long been a mystery.

Jennifer Jackson, a professor at Caltech, was at the forefront of this research. She and her team suggested in 2010 that these slow-wave regions could contain a higher concentration of iron oxide than the surrounding mantle.

The question was: could iron oxide remain solid under the extreme conditions of the CMB?

A new study Led by Jackson’s team, which includes former Caltech graduate student Vasilije Dobrosavljevic, it provides strong evidence that iron oxide can indeed remain solid at the extreme temperatures and pressures of the CMB.

They used advanced techniques such as Mössbauer spectroscopy and X-ray diffraction to observe the behavior of iron atoms under these extreme conditions.

After numerous experiments, the researchers found that iron oxide melts at temperatures above 4,000 Kelvin (around 6,700 degrees Fahrenheit) – much higher than previously thought.

This finding suggests that solid iron-rich regions in the Earth’s mantle could explain the mysterious ULVZs.

An unexpected discovery has been made about atomic defects in iron materials. Typically, iron oxide samples have tiny, regularly distributed defects in their atomic structure.

The behavior of these defects under high-pressure and high-temperature conditions, such as those present at the CMB, was previously unclear.

The team discovered that these atomic defects become disordered before iron oxide melts at lower temperatures. This disorder of defects could have been confused with melting in previous experiments.

This discovery opens new possibilities for studying the physical properties of iron-rich regions deep within the Earth.

Understanding how these defects affect heat transport and material deformation is critical to understanding planetary dynamics, including the formation of rising clouds that can reach Earth’s surface.

The findings of this study not only provide insights into the composition and behavior of materials deep within the Earth, but also pave the way for future research.

Scientists now want to explore how these discoveries impact our understanding of Earth’s evolution and the dynamic processes that shape our planet.

In summary, this study provides important clues to the enigmatic core-mantle boundary and its solid iron-rich regions, shedding light on one of the most inaccessible yet influential parts of the Earth.

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