A new study from a University of Chicago scientist suggests there may be a layer of surprisingly fluid rock ringing the Earth, at the very bottom of the upper mantle.
The finding was made by measuring the lingering movement registered by GPS sensors on islands in the wake of a deep earthquake in the Pacific Ocean near Fiji. Published Feb. 22 in Nature, the study demonstrates a new method to measure the fluidity of the Earth’s mantle.
“Even though the mantle makes up the largest part of Earth, there’s still a lot we don’t know about it,” said Sunyoung Park, a geophysicist with the University of Chicago and the lead author on the study. “We think there’s a lot more we can learn by using these deep earthquakes as a way to probe these questions.”
Mantle mysteries
We still know surprisingly little about the Earth beneath our feet. The furthest anyone has managed to dig down is about seven and a half miles before the increasing heat literally melts the drill. Thus scientists have had to use clues like how seismic waves move to infer the different layers that make up the planet, including the crust, mantle, and core.
One thing that has stymied scientists is a precise measurement of how viscous the mantle layer is. The mantle is the layer below the crust. It’s made of rock, but at the intense temperature and pressures at that depth, the rock actually becomes viscous—flowing very slowly like honey or tar.
“We want to know exactly how fast the mantle flows, because that influences the evolution of the entire Earth—it affects how much heat the planet retains for how long, and how the Earth’s materials are cycled over time,” explained Park. “But our current understanding is very limited and includes a lot of assumptions.”
Park thought there might be a unique way to get a measurement of the mantle’s properties by studying the aftermath of very deep earthquakes.
Most of the earthquakes we hear about on the news are relatively shallow, originating in the top crust of the Earth. But occasionally, there are earthquakes that originate deep within the Earth—down to 450 miles below the surface. These earthquakes are not as well-studied as shallower ones, because they’re not as destructive to human settlements. But because they reach down into the mantle, Park thought they might offer a way to understand the behavior of the mantle.
Park and her colleagues looked at one particular such earthquake, which occurred off the coast of Fiji in 2018. The quake was magnitude 8.2, but it was so deep—350 miles (560 kilometers) down—that it did not cause any major damage or deaths.
However, when the scientists carefully analyzed the data from GPS sensors on several nearby islands, they found the Earth kept moving—after the earthquake was over.
The data revealed that in the months following the quake, the Earth was still moving, settling in the wake of the disturbance. Even years later, Tonga is still moving slowly down at a rate of about 1 centimeter per year.
“You can think of it like a jar of honey that slowly comes back to level after you dip a spoon in it—except this takes years instead of minutes,” said Park.
This is the first solid observation of the deformation following deep quakes; the phenomenon had been observed before for shallow earthquakes, but experts thought the effect would be too small to be observable for deep earthquakes.
Park and her colleagues used this observation to infer the viscosity of the mantle.
By examining how the Earth deformed over time, they found evidence of a layer about 50-miles thick that is less viscous (that is, “runnier”) than the rest of the mantle, sitting at the bottom of the upper mantle layer. They think this layer may extend around the entire globe.
This low-viscosity layer could explain some other observations by seismologists that suggested there are “stagnant” slabs of rock that don’t move very much, located around the same depth at the bottom of the upper mantle. “It has been hard to reproduce those features with models, but the weak layer found in this study makes it easier to do so,” Park said.
It also has implications for how Earth transports heat, cycles and mixes materials between the crust, core, and mantle over time.
“We’re really excited,” Park said. “There’s a lot more to find out with this technique.”
The other co-authors on the paper were Jean-Philippe Avouac and Zhongwen Zhan of California Institute of Technology and Adriano Gualandi of Italy’s National Institute of Geophysics and Volcanology.
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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.
