Huge ‘blobs’ inside Earth are from another planet, study suggests

Scientists proposed a new idea Wednesday that could solve two of the world’s mysteries at once: one that goes over our heads every night, and one that sits far beneath our feet.

The first mystery has puzzled everyone from scientists to curious children for thousands of years: Where did the moon come from?

The leading theory is that the moon formed 4.5 billion years ago when a would-be Mars-sized planet collided with the still-forming Earth.

This epic collision between early Earth and the protoplanet called Theia shot a huge amount of debris into orbit, forming what would become the moon.

Or so the theory goes. Despite decades of effort, scientists have been unable to find any evidence for the existence of Theia.

New US-led research published in the journal Naturesuggests that perhaps they were looking in the wrong direction.

About 2,900 kilometers (1,800 miles) below the Earth’s surface, two enormous “blobs” have baffled geologists since seismic waves revealed their existence in the 1980s.

These continent-sized clumps of material lie at the bottom of Earth’s rocky mantle near the molten core, one beneath Africa and the other beneath the Pacific Ocean.

Scientists have determined that the blobs are much hotter and denser than the surrounding rock, but many other aspects of them remain a mystery.

Wednesday’s new research indicates that the blobs are “buried relics” of Theia that entered Earth during their formative collision — and have been hiding near the heart of our planet ever since.

In addition to creating the moon, this collision and the remnants it left behind may also have helped make Earth the unique life-hosting planet it is today, the researchers suggested.

‘Very, very strange’

Qian Yuan, a geodynamics researcher at the California Institute of Technology and lead author of the study, told AFP that it is “very, very strange” that no evidence of the Theia impact has been found.

During a class from a planetary scientist discussing this mystery, Yuan first connected the dots.

“Where is the impactor? My answer is: it is in the Earth,” he said.

The planetary scientist leading the class had never heard of the blobs. Since then, the research has required experts in the often separate fields of space travel and geology to join forces.

Yuan said that when Theia collided with the proto-Earth, it was traveling at a speed of more than 10 kilometers per second, a speed that allowed some of it to penetrate “very deeply into the Earth’s lower mantle.”

A video developed by the team simulating this process illustrates how clumps of Theia’s mantle tens of kilometers wide swirled into the Earth.

As the largely molten Theia material cooled and solidified, its high iron content caused it to sink toward the boundary of Earth’s mantle and core, the scientists suggested.

Over the years, it has accumulated into two separate blobs — officially called large low-velocity provinces (LLVPs) — each of which is now larger than the moon, Yuan said.

Testing a theory based so far back in time – and so deep beneath the Earth – is incredibly difficult, and Yuan emphasized that their models could not be “100 percent” certain.

‘Why the Earth is unique’

But if it is true, the consequences could be enormous.

Earth remains the only planet in the universe known to be capable of supporting life.

The Theia collision, believed to be Earth’s last major accretion, significantly changed its composition in just 24 hours, Yuan said.

“My feeling is that this initial condition is why Earth is unique – why it is different from other rocky planets,” he said.

Previous research has suggested that Theia could have brought water, the key ingredient of life, to Earth.

The blobs have been observed to send ‘mantle plumes’ (magma columns) towards the Earth’s surface, and have also been linked to the evolution of supercontinents.

Theia “left something in the Earth – and that played a role in the subsequent 4.5 billion years of Earth’s evolution,” Yuan said.

Christian Schroeder, an expert in both earth sciences and planetary exploration at Scotland’s University of Stirling, told AFP that the theory “fits several lines of evidence”.

“It’s a very important and exciting finding,” said Schroeder, who was not involved in the study.

He emphasized that the mystery of the moon’s formation had not yet been solved.

But the study lends more weight to the Theia impact theory — and “at the same time provides a credible explanation for these anomalies at the core-mantle boundary,” he said.

The remains of Theia that may have been preserved among us “could be responsible for important processes on Earth that continue to this day,” Schroeder added.