{"id":228351,"date":"2026-01-11T15:05:08","date_gmt":"2026-01-11T15:05:08","guid":{"rendered":"https:\/\/www.newsbeep.com\/nz\/228351\/"},"modified":"2026-01-11T15:05:08","modified_gmt":"2026-01-11T15:05:08","slug":"4-5-billion-years-ago-a-planet-may-have-smashed-into-earth-and-changed-everything","status":"publish","type":"post","link":"https:\/\/www.newsbeep.com\/nz\/228351\/","title":{"rendered":"4.5 billion years ago, a planet may have smashed into Earth and changed everything"},"content":{"rendered":"

The Moon may owe its existence to a dramatic planetary collision. About 4.5 billion years ago, a Mars-sized body called Theia smashed into the still-forming Earth, launching vast amounts of debris into orbit. Over time, that material merged to become the satellite that lights our night sky.<\/p>\n

A new study published in Nature suggests that the impact didn\u2019t just shape the Moon \u2014 it also left traces deep inside Earth itself. Fragments of Theia may have sunk into our planet\u2019s mantle, forming two mysterious, ultra-dense zones detected by geophysicists near the core.<\/p>\n

Researchers have known for decades that unusually heavy masses sit at the base of Earth\u2019s mantle, but their origin has long puzzled scientists. Using high-resolution computer models, Qian Yuan and his team at Caltech simulated the Moon-forming impact and the planet\u2019s later evolution. Their results point to buried remnants of Theia that have survived for billions of years.<\/p>\n

\u201cThis is a fascinating and provocative result,\u201d said Robin Canup of the Southwest Research Institute in Boulder, Colorado, who was not involved in the study. \u201cIt suggests Earth still holds material from Theia \u2014 clues that could reveal more about the collision that created our satellite.\u201d<\/p>\n

Voyage to the center of the Earth<\/p>\n

Picture Earth as a layered sphere rather than a simple rock. At its heart lies a blazing metal core \u2014 a liquid outer layer swirling around a dense inner core about 1,216 kilometers (756 miles) wide. Encasing it is the mantle<\/a>, which makes up roughly 80 percent of the planet\u2019s volume and supports the thin crust we live on.<\/p>\n

The mantle is Earth\u2019s engine room: tectonic plates drift and clash here, and molten rock slowly rises toward volcanoes at the surface. Because it lies so deep, scientists study it mainly through seismic waves produced by earthquakes. These waves speed up or slow down depending on the materials they pass through, allowing researchers to build a 3-D map of the planet\u2019s interior.<\/p>\n

Those seismic maps have revealed two colossal structures in the lower mantle \u2014 one under southern Africa and another beneath the Pacific Ocean. Seismic waves travel more slowly through them, which is why geologists call them Large Low-Shear-Velocity Provinces, or LLSVPs. Also known as superplumes, these dense regions appear to have existed for billions of years.<\/p>\n

How they formed remains an open question. The latest research argues that these giant patches of dense rock could be the long-buried remains of Theia \u2014 relics of the cataclysmic impact that gave birth to the Moon.<\/p>\n

Building the Moon<\/p>\n

When Theia slammed into Earth 4.5 billion years ago, the impact shattered both worlds. Clouds of vapor and molten debris wrapped around our young planet before gradually merging to form the Moon<\/a>. Over the past half-century, scientists have studied lunar samples brought back by the Apollo missions and meteorite fragments, combining that evidence with advanced computer models to build the leading theory of the Moon\u2019s origin.<\/p>\n

Still, one puzzle has long bothered geophysicist Qian Yuan: if Theia truly collided with Earth, why haven\u2019t we found any trace of it here?<\/p>\n

Yuan explored that question in his doctoral research at Arizona State University under the supervision of Mingming Li. Together, they reached out to the researchers behind existing giant-impact models.<\/p>\n

At the Shanghai Astronomical Observatory, astrophysicist Hongping Deng simulated the colossal crash and what followed \u2014 how material from both bodies might have blended, or resisted blending, inside Earth. With more detailed input data than past models, his results suggested that some of Theia\u2019s molten matter stayed behind.<\/p>\n

According to those simulations, this denser material sank deep into Earth\u2019s lower mantle, forming a distinct mass that never mixed completely with surrounding rock. \u201cI tried to make them mix,\u201d Deng said, \u201cbut they just wouldn\u2019t.\u201d<\/p>\n

Molten mixture<\/p>\n

The big question, said Robin Canup, is whether that ancient material \u201ccould really have avoided mixing and homogenizing within Earth\u2019s mantle over 4.5 billion years.\u201d<\/p>\n

Not everyone is convinced. \u201cIn our own simulations, Theia\u2019s mantle and Earth\u2019s mixed fairly well,\u201d explained planetary scientist Miki Nakajima of the University of Rochester in New York, who studies how rocky planets evolve internally.<\/p>\n

\u201cI doubt the impactor\u2019s material stayed fully separate,\u201d added geodynamicist Maxim Ballmer of University College London, \u201cbut this study underestimates how much blending occurred.\u201d Ballmer, though not part of the recent Nature paper, previously collaborated with Deng on related research.<\/p>\n

Most experts agree that these dense regions have existed in Earth\u2019s mantle for eons, but their exact age and origin remain unresolved.<\/p>\n

\u201cThere\u2019s another possible explanation,\u201d Ballmer said. One theory suggests that early Earth\u2019s mantle was once an ocean of magma that slowly differentiated into the layers we know today. The upper layer cooled quickly, solidifying as it lost heat to space, while the lower one cooled more slowly \u2014 long enough to form pockets of varying density.<\/p>\n

The next step is to compare the chemical makeup of these deep-Earth superplumes with that of the Moon, which itself is largely composed of Theia\u2019s material. \u201cIf they share the same geochemical fingerprint,\u201d Yuan said, \u201cthey must have come from the same planet.\u201d<\/p>\n

Obtaining those samples, however, will be a challenge. We can\u2019t drill down to the superplumes, but occasionally rocks from the deep mantle reach the surface \u2014 for example, in basalt<\/a> from volcanic ocean islands.<\/p>\n

Because the Moon\u2019s surface has endured billions of years of cosmic weathering and meteorite contamination, scientists also hope to study samples from its mantle. Most existing specimens come from the surface.<\/p>\n

To get new material, researchers must wait for an upcoming lunar-sample-return mission aimed at the Moon\u2019s south pole, where mantle rock is closer to the surface. Until then, they\u2019ll keep refining their models in search of Theia\u2019s lingering spectral signature.<\/p>\n

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