The large low velocity provinces (LLVPs) in the deep Earth mantle may be relics of Theian mantle materials. Credit: Deng Hongping and Hangzhou Sphere Studio
An interdisciplinary international research team has recently discovered that a massive anomaly deep within the Earth’s interior may be a remnant of the collision about 4.5 billion years ago that formed the moon.
This research offers important new insights not only into Earth’s internal structure but also its long-term evolution and the formation of the inner solar system.
The study, which relied on computational fluid dynamics methods pioneered by Prof. Deng Hongping of the Shanghai Astronomical Observatory (SHAO) of the Chinese Academy of Sciences, was published as a featured cover in Nature on Nov. 2.
The formation of the moon has been a persistent enigma for several generations of scientists. Prevailing theory has suggested that, during the late stages of Earth’s growth approximately 4.5 billion years ago, a massive collision—known as the “giant impact”—occurred between primordial Earth (Gaia) and a Mars-sized proto-planet known as Theia. The moon is believed to have formed from the debris generated by this collision.
Numerical simulations have indicated that the moon likely inherited material primarily from Theia, while Gaia, due to its much larger mass, was only mildly contaminated by Theian material.
Since Gaia and Theia were relatively independent formations and composed of different materials, the theory suggested that the moon—being dominated by Theian material—and the Earth—being dominated by Gaian material—should have distinct compositions. However, high-precision isotope measurements later revealed that the compositions of the Earth and moon are remarkably similar, thus challenging the conventional theory of moon formation.
[embedded content]MFM simulation of the canonical moon-Forming giant impact. Here different colors trace different components of Gaia and Theia. The lower mantle of Gaia, denoted by the dashed circle with a radius of 0.8 Earth radii (RE), is only marginally contaminated by Theian mantle. Credit: Bi Rongxi and Deng Hongping
While various refined models of the giant impact have subsequently been proposed, they have all faced challenges.
To further refine the theory of lunar formation, Prof. Deng began conducting research on the moon’s formation in 2017. He focused on developing a new computational fluid dynamics method called Meshless Finite Mass (MFM), which excels at accurately modeling turbulence and material-mixing.
Using this novel approach and conducting numerous simulations of the giant impact, Prof. Deng discovered that the early Earth exhibited mantle stratification after the impact, with the upper and lower mantle having different compositions and states. Specifically, the upper mantle featured a magma ocean, created through a thorough mixing of material from Gaia and Theia, while the lower mantle remained largely solid and retained the material composition of Gaia.
“Previous research had placed excessive emphasis on the structure of the debris disk (the precursor to the moon) and had overlooked the impact of the giant collision on the early Earth,” said Deng.
After discussions with geophysicists from the Swiss Federal Institute of Technology in Zurich, Prof. Deng and collaborators realized that this mantle stratification may have persisted to the present day, corresponding to the global seismic reflectors in the mid-mantle (located about 1,000 km beneath the Earth’s surface).
Specifically, the entire lower mantle of the Earth may still be dominated by pre-impact Gaian material, which has a different elemental composition (including higher silicon content) than the upper mantle, according to Prof. Deng’s previous study.
“Our findings challenge the traditional notion that the giant impact led to the homogenization of the early Earth,” said Prof. Deng. “Instead, the moon-forming giant impact appears to be the origin of the early mantle’s heterogeneity and marks the starting point for the Earth’s geological evolution over the course of 4.5 billion years.”
Another example of Earth’s mantle heterogeneity is two anomalous regions—called Large Low Velocity Provinces (LLVPs)—that stretch for thousands of kilometers at the base of the mantle. One is located beneath the African tectonic plate and the other under the Pacific tectonic plate. When seismic waves pass through these areas, wave velocity is significantly reduced.
LLVPs have significant implications for the evolution of the mantle, the separation and aggregation of supercontinents, and the Earth’s tectonic plate structures. However, their origins have remained a mystery.
Dr. Yuan Qian from the California Institute of Technology, along with collaborators, proposed that LLVPs could have evolved from a small amount of Theian material that entered Gaia’s lower mantle. They subsequently invited Prof. Deng to explore the distribution and state of Theian material in the deep Earth after the giant impact.
Through in-depth analysis of previous giant-impact simulations and by conducting higher-precision new simulations, the research team found that a significant amount of Theian mantle material, approximately 2% of Earth’s mass, entered the lower mantle of Gaia.
Prof. Deng then invited computational astrophysicist Dr. Jacob Kegerreis to confirm this conclusion using traditional Smoothed Particle Hydrodynamics (SPH) methods.
The research team also calculated that this Theian mantle material, similar to lunar rocks, is enriched with iron, making it denser than the surrounding Gaian material. As a result, it rapidly sank to the bottom of the mantle and, over the course of long-term mantle convection, formed two prominent LLVP regions. These LLVPs have remained stable throughout 4.5 billion years of geological evolution.
Heterogeneity in the deep mantle, whether in the mid-mantle reflectors or the LLVPs at the base, suggests that the Earth’s interior is far from a uniform and “boring” system. In fact, small amounts of deep-seated heterogeneity can be brought to the surface by mantle plumes—cylindrical upwelling thermal currents caused by mantle convection—such as those that likely formed Hawaii and Iceland.
For example, geochemists studying isotope ratios of rare gases in samples of Icelandic basalt have discovered that these samples contain components different from typical surface materials. These components are remnants of heterogeneity in the deep mantle dating back more than 4.5 billion years and serve as keys to understanding Earth’s initial state and even the formation of nearby planets.
According to Dr. Yuan, “Through precise analysis of a wider range of rock samples, combined with more refined giant impact models and Earth evolution models, we can infer the material composition and orbital dynamics of the primordial Earth, Gaia, and Theia. This allows us to constrain the entire history of the formation of the inner solar system.”
Prof. Deng sees an even broader role for the current study. “This research even provides inspiration for understanding the formation and habitability of exoplanets beyond our solar system.”
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NAIROBI, Kenya (AP) — The body of Ugandan Olympic athlete Rebecca Cheptegei — who died after being set on fire by her partner in Kenya — was received Friday by family and anti-femicide crusaders, ahead of her burial a day later.
Cheptegei’s family met with dozens of activists Friday who had marched to the Moi Teaching and Referral Hospital’s morgue in the western city of Eldoret while chanting anti-femicide slogans.
She is the fourth female athlete to have been killed by her partner in Kenya in yet another case of gender-based violence in recent years.
Viola Cheptoo, the founder of Tirop Angels – an organization that was formed in honor of athlete Agnes Tirop, who was stabbed to death in 2021, said stakeholders need to ensure this is the last death of an athlete due to gender-based violence.
“We are here to say that enough is enough, we are tired of burying our sisters due to GBV,” she said.
It was a somber mood at the morgue as athletes and family members viewed Cheptegei’s body which sustained 80% of burns after she was doused with gasoline by her partner Dickson Ndiema. Ndiema sustained 30% burns on his body and later succumbed.
Ndiema and Cheptegei were said to have quarreled over a piece of land that the athlete bought in Kenya, according to a report filed by the local chief.
Cheptegei competed in the women’s marathon at the Paris Olympics less than a month before the attack. She finished in 44th place.
Cheptegei’s father, Joseph, said that the body will make a brief stop at their home in the Endebess area before proceeding to Bukwo in eastern Uganda for a night vigil and burial on Saturday.
“We are in the final part of giving my daughter the last respect,” a visibly distraught Joseph said.
He told reporters last week that Ndiema was stalking and threatening Cheptegei and the family had informed police.
Four in 10 women or an estimated 41% of dating or married Kenyan women have experienced physical or sexual violence perpetrated by their current or most recent partner, according to the Kenya Demographic and Health Survey 2022.
TEL AVIV, Israel (AP) — A rare Bronze-Era jar accidentally smashed by a 4-year-old visiting a museum was back on display Wednesday after restoration experts were able to carefully piece the artifact back together.
Last month, a family from northern Israel was visiting the museum when their youngest son tipped over the jar, which smashed into pieces.
Alex Geller, the boy’s father, said his son — the youngest of three — is exceptionally curious, and that the moment he heard the crash, “please let that not be my child” was the first thought that raced through his head.
The jar has been on display at the Hecht Museum in Haifa for 35 years. It was one of the only containers of its size and from that period still complete when it was discovered.
The Bronze Age jar is one of many artifacts exhibited out in the open, part of the Hecht Museum’s vision of letting visitors explore history without glass barriers, said Inbal Rivlin, the director of the museum, which is associated with Haifa University in northern Israel.
It was likely used to hold wine or oil, and dates back to between 2200 and 1500 B.C.
Rivlin and the museum decided to turn the moment, which captured international attention, into a teaching moment, inviting the Geller family back for a special visit and hands-on activity to illustrate the restoration process.
Rivlin added that the incident provided a welcome distraction from the ongoing war in Gaza. “Well, he’s just a kid. So I think that somehow it touches the heart of the people in Israel and around the world,“ said Rivlin.
Roee Shafir, a restoration expert at the museum, said the repairs would be fairly simple, as the pieces were from a single, complete jar. Archaeologists often face the more daunting task of sifting through piles of shards from multiple objects and trying to piece them together.
Experts used 3D technology, hi-resolution videos, and special glue to painstakingly reconstruct the large jar.
Less than two weeks after it broke, the jar went back on display at the museum. The gluing process left small hairline cracks, and a few pieces are missing, but the jar’s impressive size remains.
The only noticeable difference in the exhibit was a new sign reading “please don’t touch.”
VICTORIA – The British Columbia government is partnering with a bear welfare group to reduce the number of bears being euthanized in the province.
Nicholas Scapillati, executive director of Grizzly Bear Foundation, said Monday that it comes after months-long discussions with the province on how to protect bears, with the goal to give the animals a “better and second chance at life in the wild.”
Scapillati said what’s exciting about the project is that the government is open to working with outside experts and the public.
“So, they’ll be working through Indigenous knowledge and scientific understanding, bringing in the latest techniques and training expertise from leading experts,” he said in an interview.
B.C. government data show conservation officers destroyed 603 black bears and 23 grizzly bears in 2023, while 154 black bears were killed by officers in the first six months of this year.
Scapillati said the group will publish a report with recommendations by next spring, while an independent oversight committee will be set up to review all bear encounters with conservation officers to provide advice to the government.
Environment Minister George Heyman said in a statement that they are looking for new ways to ensure conservation officers “have the trust of the communities they serve,” and the panel will make recommendations to enhance officer training and improve policies.
Lesley Fox, with the wildlife protection group The Fur-Bearers, said they’ve been calling for such a committee for decades.
“This move demonstrates the government is listening,” said Fox. “I suspect, because of the impending election, their listening skills are potentially a little sharper than they normally are.”
Fox said the partnership came from “a place of long frustration” as provincial conservation officers kill more than 500 black bears every year on average, and the public is “no longer tolerating this kind of approach.”
“I think that the conservation officer service and the B.C. government are aware they need to change, and certainly the public has been asking for it,” said Fox.
Fox said there’s a lot of optimism about the new partnership, but, as with any government, there will likely be a lot of red tape to get through.
“I think speed is going to be important, whether or not the committee has the ability to make change and make change relatively quickly without having to study an issue to death, ” said Fox.
This report by The Canadian Press was first published Sept. 9, 2024.
