Ancient magma ocean reshapes understanding of Earth's mantle

Early Earth history holds many mysteries, one of which is the existence of a deep ocean of magma beneath the planet's surface. A new study published in the scientific journal Nature found that not only could a magma ocean exist, but its presence was inevitable. Regardless of the exact location where the molten newborn planet began to crystallize into a solid body, a basal ocean was still forming. This could also trigger contemporary seismic phenomena.

Charles-Édouard Boukaré, the study’s lead author, suggested that this may have affected the way heat is transferred between the Earth’s core and mantle. This discovery could also explain the presence of large areas in the mantle where seismic waves move more slowly.

Research indicates that the magma ocean may have formed at the core-mantle boundary of Earth within the first few hundred million years of its existence. Models suggest that even if the planet crystallized from the bottom up, the magma ocean was inevitable. Boukaré told "Live Science" that no matter the point at which crystallization began, the formation of the magma ocean was already underway.

Traces of this hidden sea of magma may exist today in the form of LLVPs (Large Low-Shear-Velocity Provinces) or "blobs" in the mantle. LLVP stands for "Large Low-Shear-Velocity Provinces," indicating extensive anomalies in the Earth's lower mantle where seismic waves move slower than normal. Scientists have debated whether these anomalies are remnants of oceanic crust that were pushed deep into the mantle, meaning they are a few hundred million years old, or if they are remnants of Earth's primordial magma ocean, suggesting they are 4.4 billion years old.

The new study supports the latter option, and the findings could significantly impact how scientists understand Earth's history, said Charles-Édouard Boukaré, the lead author of the study and a planetary physicist at York University in Toronto. "It would affect thermal communication between the core and the mantle," Boukaré told "Live Science." He believes it could also influence the positioning of tectonic plates.

To prove this, scientists created a new model of Earth's formation, which incorporated both geochemical data and seismic data—two main methods of probing Earth's deep history. In particular, there are important trace elements that chemically prefer to remain in magma, while other minerals crystallize into rock. The amount of these trace elements in the rock can reveal when and in what order mantle rocks solidified.

Most research into this era of Earth's formation focuses on the initial solidification of the mantle and its dynamics when the mantle was still mostly liquid. Boukaré and his team found that regardless of where solidification first began—whether in the middle of the mantle or right at the boundary with the core—a basal magma ocean formed.

This discovery could be significant for understanding Earth's history. "We can then predict most of its behavior on long timescales," Boukaré adds. Research suggests that the planet's structure was shaped very early, and ancient structures continue to influence its evolution.

Scientists plan further research to better understand how these ancient magma oceans could have affected other planets, such as Mars. "Maybe this basal ocean thing is not something that is unique to the Earth," Boukaré wonders.