The Leading Explanation for How the Moon Was Born Is that a World the Size of Mars Called Theia Slammed Into the Young Earth and Flung Out the Debris that Became the Moon, and Recent Research Suggests Theia Itself Never Fully Left, with Two Continent-Sized Blobs Buried Near Our Planet’s Core Possibly Being the Last Remains of the World that Struck Us.

Why It Matters

If the LLVPs are relics of Theia, they provide a tangible record of the Moon‑forming impact, offering a novel avenue to test planetary‑formation models and refine our understanding of early Earth dynamics.

Key Takeaways

• Giant-impact hypothesis remains leading explanation for Moon formation
• LLVPs under Africa and Pacific may be remnants of Theia’s mantle
• 2023 study models dense Theian fragments sinking to Earth’s core
• Isotopic similarity between Earth and Moon challenges simple impact models
• Future geochemical probes could test Theia‑origin hypothesis for deep mantle blobs

Pulse Analysis

The giant‑impact hypothesis, first proposed in the 1970s, continues to dominate explanations for the Moon’s origin. By positing that a Mars‑sized protoplanet—named Theia—collided with the early Earth, the model accounts for the Moon’s large relative size, the system’s angular momentum, and the satellite’s small iron core. Yet a persistent puzzle remains: high‑precision isotopic analyses show Earth and Moon rocks share nearly identical oxygen, titanium and tungsten signatures, a result difficult to reconcile with a simple mixing of two distinct bodies. Researchers therefore seek refinements that preserve the model’s explanatory power while resolving the isotopic conundrum.

Seismic imaging over the past four decades has revealed two massive low‑velocity provinces (LLVPs) at the base of the mantle, one beneath Africa and another beneath the Pacific. Their size rivals small continents, and their composition appears denser than surrounding mantle material. In a 2023 Nature paper, Qian Yuan’s team simulated an impact where Theia’s mantle was iron‑rich, producing fragments 2–3.5 % denser than Earth’s mantle. The models showed these blobs could descend through the mantle and accumulate atop the core, reproducing the observed LLVP geometry. While the study stops short of proof, it offers a physically plausible pathway linking the Moon‑forming event to deep‑Earth anomalies.

The prospect that remnants of Theia survive deep within Earth reshapes how planetary scientists view early Solar System dynamics. If LLVPs retain a distinct chemical fingerprint, mantle plumes could transport trace elements to the surface, providing a testable signal for deep‑mantle sampling missions or high‑precision volcanic glass analyses. Confirming a Theian origin would also tighten constraints on impact angles, velocities and the iron budget of the colliding bodies, refining models of lunar accretion. Conversely, disproving the link would push researchers toward alternative explanations for both the isotopic similarity and the enigmatic low‑velocity provinces, keeping the debate vibrant.