Scientists say they might have figured out why the geological process of rocks rising and sinking in the Earth's molten core has suddenly stopped. 

Using computer simulations, researchers examined the stagnant slabs of rocky tectonic plate in the Pacific Ocean and discovered a layer of obstructive material that is causing the phenomenon. 

The findings were published in the journal Nature Geoscience. 

Stagnant Slabs

The existence of stagnant slabs has been puzzling scientists for about a decade now. A system called mantle convection in which hotter rocks rise up while colder rocks sink down in the planet's molten core has been in place for millions of billions of years. However, about a decade ago, scientists discovered that the process inexplicably and without warning stopped. 

Giant slabs of subducted oceanic plates in the process of a slow descent into the molten core somehow got stuck. University of Colorado Boulder researchers Wei Mao and Shijie Zhong think they know why. 

In the study, the researchers suggested the existence of a thin layer of less-viscous rock positioned in between of two halves of the mantle. They arrived at this conclusion by observing the stagnant slabs in the western Pacific Ocean, specifically off the east coast of Japan and below the Mariana Trench near the Philippines.  

The slabs in Asia, according to the researchers, do not go down as normal. Instead, they spread out horizontally between the upper and lower mantle of the Earth. 

"If you introduce a weak layer at that depth, somehow the reduced viscosity helps lubricate the region," explained Zhong. "The slabs get deflected and can keep going for a long distance horizontally."

This only happens in the slabs in Asia. Similar slabs in North and South America go about their normal process: they dive into the lower mantle where the core heats them up again. Zhong explains that there is more room in Asia for the chunks of rocks to slide, but not in the Americas. 

Going Back To Normal

The researchers, however, assured that the stagnant slabs will not cause any issues. However, it completely changes the way scientists study volcanism and tectonics on the surface of the Earth. 

The researchers also think that the stagnant slab phenomenon is not permanent. Things will eventually go back to normal when the slabs break through and continue their descent to the planet's core. When it will happen, no one knows for now.