Huge “islands” found inside Earth are 100 times taller than Everest

Geoscientists Discover Two Continent-Sized Regions Hiding Beneath Earth’s Mantle

In a groundbreaking finding published in the journal Nature, scientists from Utrecht University have identified two massive, continent-sized regions lurking deep within Earth’s mantle. Dubbed Large Low Seismic Velocity Provinces (LLSVPs), these hidden landmaves are roughly 1,200 miles (2,000 km) beneath our feet and tower an astounding 620 miles (1,000 km) high, dwarfing every mountain peak on Earth’s surface and every other planet in our solar system.

The existence of these subterranean islands was first suspected in the late 20th century through seismic analysis. Large earthquakes cause the Earth to resonate like a bell, with oscillations revealing subsurface anomalies. The studies showed the presence of what are now called Large Low Seismic Velocity Provinces (LLSVPs).

Until now, it was believed that Earth’s mantle was a well-mixed and rapidly flowing system. However, the discovery of these ancient, stable structures challenges this notion. These "islands" appear to have been sitting undisturbed for millions, perhaps even billions, of years, defying conventional models that posit a uniform, well-mixed mantle.

To study these deep regions, seismologists rely on oscillations caused by massive earthquakes, particularly those occurring at substantial depths. A team led by study senior author Arwen Deuss, a seismologist at Utrecht University, delved into these zones using sophisticated seismic analysis techniques.

Against expectations, the researchers found that while LLSVPs slow down seismic waves, they do not dampen them significantly. This contradicts previous assumptions based on the behavior of waves in the hotter upper mantle, where both slowing and damping are observed.

Mineralogical analyses suggested by study co-author Laura Cobden indicate that grain size plays a pivotal role. The cold slab graveyard, where tectonic plates recrystallize into small grains as they sink into the mantle, results in substantial energy loss due to numerous grain boundaries. In stark contrast, the LLSVPs consist of much larger grains, allowing waves to pass with minimal damping.

These findings suggest that LLSVPs are much older than the surrounding slab graveyards. Since mineral grains take time to grow, this implies that LLSVPs have been relatively unchanged for vast expanses of time.

The discovery of these hidden islands has profound implications for understanding Earth’s evolution. The mantle drives surface phenomena such as volcanism and mountain building. Mantle plumes, believed to originate at the edges of LLSVPs, eventually cause volcanic activity, such as the eruptions seen in Hawaii.

Scientists now need to better understand the formation and behavior of these enigmatic regions to gain a more comprehensive picture of Earth’s complex inner workings. The study is published in the journal Nature.