Earth's interior isn't a uniform stack of layers. There are two huge blobs of thermo-chemical material in the middle layer.
Scientists don't know where the structures came from or why they have different heights, but a new set of models has come up with a possible answer.
The blob under the African continent is more than twice as high as the one under the Pacific ocean, according to the deep propagation of seismic waves.
After running hundreds of simulations, the authors of the new study think the blob under the African continent is less dense and less stable than the Pacific counterpart.
The initial volume of the blobs doesn't affect their height according to the calculations.
The height of the blobs is mostly controlled by how dense they are.
The blob is in the mantle beneath Africa. Is itming Li/ASU.
The mantle is a layer of silicate rock that sits between the planet's core and its crust. The mantle behaves like tar on longer timescales.
Columns of hot magma rock gradually rise through the mantle and are thought to contribute to volcanic activity on the planet's surface.
Understanding what is happening in the mantle is an important endeavor in geology.
The blobs of the Pacific and African were first discovered. These are referred to as large low-shear-velocity provinces.
The African LLSVP is about 1,000 kilometers higher than the Pacific, which supports previous estimates.
Both of these blobs have different compositions. How this affects the surrounding mantle is not known.
The less stable nature of the African pile might explain why there is so much volcanism in some regions. It could affect the movement of plates on the mantle.
The African LLSVP is up to 1,500 kilometers above the outer core, while the Pacific is up to 800 kilometers high.
The African and Pacific piles seem to move up and down through the mantle in lab experiments.
The authors of the current study say that this supports their interpretation that the African LLSVP is probably unstable, and that the same could happen for the Pacific.
The origins of the Pacific and African LLSVPs can be explained. There are two main theories as to where these blobs came from.
The piles are made from subducted tectonic plates, which slip into the mantle, are super-heated and gradually fall downwards, contributing to the blob.
There is a theory that the blobs are remnants of the ancient collision between Earth and Thea.
The theories are not exclusive. Thea may have contributed more to one blob than the other way around.
New insights on the nature of the Earth's largest structures in the deep interior and their interaction with the surrounding mantle are provided by the combination of the analysis of seismic results and the geodynamic modeling.
This work has far-reaching implications for scientists trying to understand the present-day status and the evolution of the deep mantle structure.
The study was published in a journal.
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