Weird blobs lurking near Earth’s core may have been dragged from the surface

A new study suggests that strange “blobs” found deep in Earth’s middle layer may be pieces of ancient continental crust that were pulled down by tectonic forces.

These blobs, known as ultra-low-velocity zones (ULVZs), have long puzzled scientists. It’s deep in the mantle, near the boundary with Earth’s core, so researchers can only see it by studying earthquake waves that resonate around the planet’s interior like a bell. These waves slow down significantly in regions of the bubble, indicating that they are different from the surrounding mantle.

In the new study published on April 17 in the journal JGR solid groundThe researchers suggest that these regions may be more widespread than previously thought, and that their composition varies greatly from one point to another.

“There are more of these materials out there,” says the study’s lead author Samantha Hansen“Whatever that material is,” a geologist at the University of Alabama told Live Science.

Related: Two giant blobs in Earth’s mantle may explain Africa’s strange geology

In 2012, Hansen and her team began a project to study the upper mantle through a network of earthquake monitors in Antarctica, but they soon realized they had a unique data set. To image the lower mantle with seismic waves, scientists need the right mix of earthquake sites and sensors, she said, and Antarctica has provided a new window into the structures beneath the Southern Hemisphere.

Map of permanent broadband seismic stations that have reported data to the combined research institutions of the Earthquake Data Management Center since January 1, 2010.

Map of permanent broadband seismic stations that have reported data to the combined research institutions of the Earthquake Data Management Center since 1 January 2010. The Global Seismic Network (GSN) and its affiliated stations are shown with green stars, with labels indicating station code and ratings in parentheses (out of 150 GSN station) used by the National Earthquake Information Center for locations of primary earthquakes during a one-year period (July 14, 2019 to July 14, 2020). The GSN station in the Pacific Antarctica, Antarctica (QSPA) is the only permanent broadband station in the 12° region, approximately the size of the combined Mountain West and Great Plains regions of the United States (enter). (Image credit: Anthony, RE, AT Ringler, M. DuVernois, KR Anderson, and DC Wilson (2021))

“One of the big advantages of using Antarctic stations is that they allow us to examine a part of the lower mantle that has never been looked at before,” Hansen said.

When scientists analyzed the data, they found ULVZs widespread in the Southern Hemisphere, the team reported April 17 in the journal. JGR solid ground. They also modeled global subduction, or the phenomenon of oceanic crust sinking into the mantle. Currently this is happening in Subduction zones Such as those around the Pacific “Ring of Fire,” where earthquakes and volcanoes are common. The ULVZs appear to be in locations that would be expected if they were ancient oceanic crust that fell toward the Earth’s center by subduction.

“Our best explanation is that it is related to subducted material,” Hansen said.

There are other hypotheses about the ULVZ, including that they are simply mantle zones with temperature changes that cause partial melting, which could change the way earthquake waves move through them. Another hypothesis says that they are remnants The collision of planets that created the moon. But subduction may explain why not all ULVZs are created equal, Hansen said.

“This wide distribution of reported ULVZ properties is likely explained by the fact that the material itself is variable,” she said.

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