Discovery: Ancient ocean floor surrounds the Earth’s core

Scientists from the University of Alabama have discovered a dense layer of ocean floor material that covers the boundary between the Earth’s core and mantle, according to a study published in the journal Science Advances. 

This layer of ancient ocean floor was likely subducted underground as the Earth’s plates shifted, making it denser than the rest of the deep mantle, and it slows seismic waves reverberating beneath the surface. This ultra-low velocity zone (ULVZ) was previously seen only in isolated patches but has now been found to exist across a large region.

“Seismic investigations, such as ours, provide the highest resolution imaging of the interior structure of our planet, and we are finding that this structure is vastly more complicated than once thought,” said study lead author Dr. Samantha Hansen. “Our research provides important connections between shallow and deep Earth structure and the overall processes driving our planet.”

The layer is only tens of kilometers thick, compared to the thickness of the Earth’s dominant layers. This thin layer was detected through high-resolution imaging of seismic signals, which were used to map a variable layer of material across the study region. The properties of the anomalous core-mantle boundary coating include strong wave speed reductions, leading to the name of ultra-low velocity zone.

“Analyzing 1000’s of seismic recordings from Antarctica, our high-definition imaging method found thin anomalous zones of material at the CMB everywhere we probed.” said study co-author Dr. Edward Garnero, a geophysicist at Arizona State University who co-led the research. “The material’s thickness varies from a few kilometers to 10’s of kilometers. This suggests we are seeing mountains on the core, in some places up to 5 times taller than Mt. Everest.”

These underground “mountains” are thought to be former oceanic seafloors that have sunk to the core-mantle boundary. They may play an important role in how heat escapes from the core, which powers the magnetic field. Additionally, material from the ancient ocean floors can also become entrained in mantle plumes or hot spots, which travel back to the surface through volcanic eruptions.

The discovery of this layer provides important insights into the structure and processes of our planet, and it underscores the importance of continued exploration and study of the Earth’s interior. 

“This is a really exciting result, and it provides a critical piece of information for understanding how the Earth works,” said Dr. Garnero. “It’s fascinating to think that we can learn so much about our planet just by listening to the echoes of earthquakes.”

The core-mantle boundary, located approximately 2,000 miles below Earth’s surface, is coated with an ultra-low velocity zone (ULVZ) that ranges from a few kilometers to tens of kilometers thick. This coating was discovered through a seismic network that collected data over three years during four trips to Antarctica.

The team, which included students and researchers from various countries, used 15 stations in the network buried in Antarctica that used seismic waves created by earthquakes from around the world to create an image of the Earth’s interior. The technique is similar to a medical scan of the body. The team was able to probe a large portion of the southern hemisphere in high resolution for the first time using this method.

“We found thin anomalous zones of material at the CMB (core-mantle boundary) everywhere we probed,” said Dr. Garnero. “The material’s thickness varies from a few kilometers to tens of kilometers. This suggests we are seeing mountains on the core, in some places up to 5 times taller than Mt. Everest.”

The ULVZs are thought to be former oceanic seafloors that sank to the core-mantle boundary. Oceanic material is carried into the interior of the planet where two tectonic plates meet and one dives beneath the other, known as subduction zones. 

Accumulations of subducted oceanic material collect along the core-mantle boundary and are pushed by the slowly flowing rock in the mantle over geologic time. The distribution and variability of such material explains the range of observed ULVZ properties.

The ULVZs are comparable to mountains along the core-mantle boundary, with heights ranging from less than about 3 miles to more than 25 miles. The team believes that these underground “mountains” may play an important role in how heat escapes from the core, the portion of the planet that powers the magnetic field. Material from the ancient ocean floors can also become entrained in mantle plumes, or hot spots, that travel back to the surface through volcanic eruptions.

The discovery of the ULVZs and their potential implications for Earth’s heat and magnetic fields provides new insights into the planet’s inner workings, and underscores the importance of continued research in this field.

What else we know about the Earth’s core

The Earth’s core is the central part of our planet and is divided into two parts: the inner core and the outer core. The inner core is a solid sphere with a radius of about 1,220 kilometers and is believed to be composed mainly of iron and nickel. The outer core, on the other hand, is a liquid layer that surrounds the inner core and has a thickness of about 2,200 kilometers.

The temperature of the Earth’s core is estimated to be around 6,000 degrees Celsius (10,800 degrees Fahrenheit), which is hotter than the surface of the sun. This extreme heat is generated by the process of radioactive decay and the residual heat left over from the planet’s formation.

The Earth’s core also plays a critical role in the generation of our planet’s magnetic field. The motion of the liquid outer core, coupled with the rotation of the Earth, produces a dynamo effect that generates the magnetic field that protects our planet from harmful solar radiation and cosmic particles.

Despite our knowledge about the Earth’s core, there is still much that remains unknown. Scientists are still trying to determine the exact composition of the core and how the heat generated in the core is transferred to the rest of the planet. This is important for understanding the behavior of the Earth’s interior, including the formation of earthquakes and volcanic activity.

In recent years, new technologies such as seismic tomography have allowed scientists to study the Earth’s core in more detail than ever before. These advances are helping us to better understand the mysteries of the Earth’s interior, and we can expect more exciting discoveries in the years to come.

—

Check us out on EarthSnap, a free app brought to you by Eric Ralls and Earth.com.