An immense impact event involving the early protoplanet Theia and the proto-Earth approximately 4.5 billion years ago is theorized to have not only sculpted Earth’s Moon but also engendered two colossal, continent-sized anomalies—officially designated as large low-velocity provinces (LLVPs)—deep within Earth’s mantle, according to findings from a scientific consortium spearheaded by researchers at Caltech.
During the 1980s, scientific inquiry revealed the presence of two distinct, continent-scale aggregations of anomalous material situated in the profound depths of Earth’s interior: one situated beneath the African landmass and the other beneath the Pacific Ocean.
Each of these massive structures is estimated to be twice the dimension of our Moon and is presumed to possess elemental compositions divergent from the surrounding mantle.
The provenance of these peculiar formations, officially cataloged as large low-velocity provinces (LLVPs), remains a subject of intense scientific investigation.
“The terminal phase of terrestrial planet development is characterized by a series of colossal collisions between planetary embryos comparable in size to the Moon and Mars,” stated Caltech investigator Qian Yuan and his collaborators.
“The widely examined giant-impact hypothesis posits a collision between a protoplanet, identified as Theia, and the proto-Earth.”
Within the framework of their research, the authors employed sophisticated computational modeling to postulate a plausible explanation for the existence of LLVPs.
Evidence suggests that the material constituting these regions exhibits a density between 2.0% and 3.5% greater than that of the ambient mantle.
The simulations indicate that the LLVPs might be preserved vestigies of Theia’s mantle material, having been retained within the proto-Earth’s mantle subsequent to the moon-forming cataclysmic impact.
It is proposed that these Theia remnants, originally spanning tens of kilometers in extent, descended to the lower mantle strata and coalesced to form dense masses situated atop the Earth’s core.
“A direct implication of the hypothesis that LLVPs are remnants of Theia is their profound antiquity,” observed Dr. Paul Asimow, also affiliated with Caltech.
“Consequently, it is logical to next explore their influence on Earth’s nascent geological evolution, encompassing the initiation of subduction prior to the emergence of conditions conducive to modern plate tectonics, the genesis of the earliest continents, and the origin of the most ancient surviving terrestrial minerals.”
“Our findings challenge the prevailing consensus that the giant impact resulted in the complete homogenization of the early Earth,” remarked Professor Hongping Deng, a researcher at the Shanghai Astronomical Observatory.
“On the contrary, the moon-forming giant impact appears to be the source of the early mantle’s heterogeneity and marks the inception of Earth’s geological trajectory spanning 4.5 billion years.”
“While the Moon contains materials indicative of both the pre-impact Earth and Theia, it was previously assumed that any remnants of Theia within Earth would have been ‘obliterated’ and homogenized by eons of dynamic processes (such as mantle convection) within the planet,” explained Professor Steven Desch of Arizona State University.
“This investigation is the inaugural study to present the compelling argument that distinct ‘fragments’ of Theia persist within Earth, specifically at its core-mantle boundary.”
“It appears that Earth’s subterranean anomalies are indeed vestiges of a planetary collision that culminated in the formation of our Moon,” stated Professor Ed Garnero from Arizona State University.
“In essence, the colossal formations currently residing deep within Earth, beneath our feet, are extraterrestrial in origin. Consequently, Earth not only harbors ‘blobs’ but also extraterrestrial ones!”
“Through meticulous examination of an expanded array of rock samples, coupled with more sophisticated giant impact and Earth evolution models, we can deduce the material composition and orbital dynamics of the primordial Earth, known as Gaia, and Theia,” elaborated Dr. Yuan.
“This analytical approach enables us to delineate the comprehensive history of the inner Solar System’s formation.”
“This groundbreaking research even offers valuable insights for comprehending the formation and potential habitability of exoplanets situated beyond our Solar System,” concluded Professor Deng.
The study has been formally published in the esteemed journal Nature.
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Q. Yuan et al. 2023. Moon-forming impactor as a source of Earth’s basal mantle anomalies. Nature 623, 95-99; doi: 10.1038/s41586-023-06589-1
