Two Continent-Sized 'Blobs' Hidden Deep Inside Earth's Mantle Continue To Baffle Scientists From Decades

Earth and many of its features are still an enigma for experts. The most prominent mystery is possibly that of the mantle. The mantle is to date, unreachable, stated EOS. Certain growths in the mantle have been detected that continue to boggle researchers even after decades. Some findings regarding these growths have been published in the journal Nature.

These growths have been observed 2,000 miles below the Earth's surface. Due to the perceived shape of these growths, they have been labeled as blobs. They were first discovered some four decades ago. Scientists used seismic tomography to detect these blobs. Any earthquake sends waves underneath the surface, scientists essentially calculated the time these waves took to come back to the surface. The scientists assumed that the waves are hit by any development inside the surface and come back after colliding with it. Based on recordings from several instruments, a picture of Earth's interior was formulated. 

The exercise produced results that were absolutely surprising to researchers. "It was very clear in those models from the get-go that at the bottom of Earth’s mantle, nearly halfway to the center, there were these huge zones where the waves traveled more slowly," said Ed Garnero, professor of Earth and space exploration at Arizona State University. The blobs were present in the slow-wave velocity zones. One of them was under the Pacific Ocean, while the other one was underneath Africa and part of the Atlantic Ocean. "They’re basically unmissable," said seismologist Karin Sigloch at the University of Oxford. "They just show up on everybody’s pictures."

The team was instantly intrigued and wanted to know more about the blobs. These blobs and all other mantle features are valuable because they supposedly influence Earth's processes. "Ultimately, a lot of people believe plate tectonics is one of the reasons why we have life on Earth," said geophysicist Harriet Lau at Harvard University. Scientists claim that these blobs are the continents and stretch 100 times more than Mount Everest. Its exact location is at the foot of Earth’s rocky mantle and just above the molten outer core. Experts think that these blobs are made of rocks. Some assume that there is a possibility that they are hotter and heavier than their surrounding mantle.

Even after decades of discovery, the blobs remain a question mark for experts. This is primarily because, currently, the technology is not equipped enough to reach these so-called blobs. "We know less about what’s deep below our feet than the surface of the Sun or the Moon or Mars," said University College London researcher Paula Koelemeijer. To understand more about the blobs, it is necessary that their inner composition is unveiled. Two sets of researchers have applied specific methodologies to unveil the density of these blobs.

Harriet Lau, a postdoctoral researcher at Harvard University, took into consideration a decade's worth of Earth tide measurements collected by a team led by Linguo Yuan at Academia Sinica in Taiwan and made several models investigating the tides. "It just so happens that body tides, or solid Earth tides, are very sensitive to density structure," Lau said. The models aligned with real-world data only when blobs were considered to be denser than the surrounding mantle.

The other examination had Paula Koelemeijer, a research fellow, trying to understand the density of blobs using Stoneley waves. These kinds of waves vibrate based on the density of the thing they are clashing with in the process. The team analyzed the patterns of Stoneley waves in the days following large-magnitude earthquakes and concluded that blobs must be less dense than the surrounding mantle. These wide-ranging speculations indicate the expansiveness of the structure. "One way to perhaps reconcile Harriet Lau and my work is that this dense material is not distributed over a very large depth range," Koelemeijer explained. She is hopeful that more such examinations, bring experts closer to solving the blob conundrum.