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Researchers solve mystery of Earth's vanishing crust – lintelligencer

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Researchers solve mystery of Earth’s vanishing crust

Thank goodness for the Earth’s crust: It is, after all, that solid, outermost layer of our planet that supports everything above it.

But much of what happens below that layer remains a mystery, including the fate of sections of crust that vanish back into the Earth. Now, a team of geochemists based at the Florida State University-headquartered National High Magnetic Field Laboratory has uncovered key clues about where those rocks have been hiding.

The researchers provided fresh evidence that, while most of the Earth’s crust is relatively new, a small percentage is actually made up of ancient chunks that had sunk long ago back into the mantle then later resurfaced. They also found, based on the amount of that “recycled” crust, that the planet has been churning out crust consistently since its formation 4.5 billion years ago—a picture that contradicts prevailing theories.

Their research is published in the journal Science Advances.

“Like salmon returning to their spawning grounds, some oceanic crust returns to its breeding ground, the volcanic ridges where fresh crust is born,” said co-author Munir Humayun, a MagLab geochemist and professor at Florida State’s Department of Earth, Ocean and Atmospheric Science (EOAS). “We used a new technique to show that this process is essentially a closed loop, and that recycled crust is distributed unevenly along ridges.”

In addition to Humayun, the research team included MagLab postdoctoral researcher Shuying Yang, lead author on the paper, and MagLab Geochemistry Group Director and EOAS Chair Vincent Salters.

The Earth’s oceanic crust is formed when mantle rock melts near fissures between tectonic plates along undersea volcanic ridges, yielding basalt. As new crust is made, it pushes the older crust away from the ridge toward continents, like a super slow conveyer belt. Eventually, it reaches areas called subduction zones, where it is forced under another plate and swallowed back into the Earth.

Scientists have long theorized about what happens to subducted crust after being reabsorbed into the hot, high-pressure environment of the planet’s mantle. It might sink deeper into the mantle and settle there, or rise back to the surface in plumes, or swirl through the mantle, like strands of chocolate through a yellow marble cake. Some of that “chocolate” might eventually rise up, re-melt at mid-ocean ridges, and form new rock for yet another millions-year-long tour of duty on the sea floor.

This new evidence supports the “marble cake” theory.

Scientists had already seen clues supporting the theory. Some basalts collected from mid-ocean ridges, called enriched basalts, have a higher percentage of certain elements that tend to seep from the mantle into the melt from which basalt is formed; others, called depleted basalts, had much lower levels.

To shed more light on the mystery of the disappearing crust, the team chemically analyzed 500 samples of basalt collected from 30 regions of ocean ridges. Some were enriched, some were depleted and some were in between.

Early on, the team discovered that the relative proportions of germanium and silicon were lower in melts of recycled crust than in the “virgin” basalt emerging from melted mantle rock. So they developed a new technique that used that ratio to identify a distinct chemical fingerprint for subducted crust.

They devised a precise method of measuring that ratio using a mass spectrometer at the MagLab. Then they crunched the numbers to see how these ratios differed among the 30 regions sampled, expecting to see variations that would shed light on their origins.

At first the analysis revealed nothing of note. Concerned, Yang, a doctoral candidate at the time, consulted with her adviser. Humayun suggested looking at the problem from a wider angle: Rather than compare basalts of different regions, they could compare enriched and depleted basalts.

After quickly re-crunching the data, Yang was thrilled to see clear differences among those groups of basalts.

“I was very happy,” recalled Yang, lead author on the paper. “I thought, ‘I will be able to graduate!’”

The team had detected lower germanium-to-silicon ratios in enriched basalts—the chemical fingerprint for recycled crust—across all the regions they sampled, pointing to its marble cake-like spread throughout the mantle. Essentially, they solved the mystery of the vanishing crust.

It was a lesson in missing the forest for the trees, Humayun said.

“Sometimes you’re looking too closely, with your nose in the data, and you can’t see the patterns,” he said. “Then you step back and you go, ‘Whoa!’”

Digging deeper into the patterns they found, the scientists unearthed more secrets. Based on the amounts of enriched basalts detected on global mid-ocean ridges, the team was able to calculate that about 5 to 6 percent of the Earth’s mantle is made of recycled crust, a figure that sheds new light on the planet’s history as a crust factory. Scientists had known the Earth cranks out crust at the rate of a few inches a year. But has it done so consistently throughout its entire history?

Their analysis, Humayun said, indicates that, “The rates of crust formation can’t have been radically different from what they are today, which is not what anybody expected.”

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Grizzly bears in the dark as they try to share living space with humans: study – BayToday

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EDMONTON — Grizzly bears are doing their best to get along with people, but it still isn’t enough.

Newly published research concludes that without large wilderness areas to replenish their numbers, grizzlies would disappear from landscapes they share with humans.

“The persistence of bears near people, when we see them along highways or near towns, they’re really propped up by the fact they exist near some sort of secure wilderness,” said Clayton Lamb, a University of Alberta biologist and lead author of a paper published in the Proceedings of the National Academy of Sciences.

Researchers found bears in populated areas in Alberta and British Columbia have even changed how they hunt in an attempt to share living space with humans.

“The bears are doing what they can,” Lamb said. “The difference might have to be made up by us.”

The study set out to examine an emerging phenomenon in wildlife conservation — large carnivores re-establishing themselves on mixed landscapes including cities, highways, rural communities and patchworks of natural habitat.

It digested 41 years worth of mortality, movement and demography among 2,669 grizzlies over nearly 400,000 square kilometres of British Columbia.

It found mortality has increased steeply with the amount of human impact measured through an index that includes human population, land use, infrastructure, coastlines, roads, railroads and navigable rivers.

Deaths have outnumbered births and the difference is being made up through emigration of young grizzlies from nearby wilderness. For every point the index increases, a local bear population must increase the number of individuals it draws by about two per cent.

“Grizzly bear range is quite tied to the distance from some secure piece of wilderness,” said Lamb.

That’s despite the grizzlies’ efforts to adapt to humans. The study found young, newly arrived bears gradually learned ways to avoid contact, such as hunting and gathering at night.

Adolescent bears in areas dominated by humans have increased their nocturnal time by up to three per cent annually, which has led to corresponding increases in survival. The cost, however, is steep. 

The scientists found it takes 14 years for a grizzly to learn how to co-exist with humans. For every bear that makes it, 29 don’t. 

“A lot of those bears would have been born on a mountaintop 10 kilometres away and lived with mom in an avalanche chute and lived a normal bear life,” Lamb said.

“Then they find a home near town and get lured in by an apple tree. The gauntlet they have to run is very difficult.”

The study shows that high mortality has impacts far from where the deaths take place. Bears dying in mixed-used areas draws more grizzlies from the wilderness to take their place. 

“Conflicts with people have rippling effects on (bear) populations far removed,” Lamb said. 

Highway overpasses are one good way to reduce deaths, he suggests. But humans living with bears have to get better at removing attractants such as roadkill or fruit trees to end the bears’ constant, often fatal, migration from the wilderness.  

“We’re not quite there,” said Lamb. “The system relies quite heavily on adjacent wilderness.”

This report by The Canadian Press was first published July 7, 2020

— Follow @row1960 on Twitter

Bob Weber, The Canadian Press

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Bear population attempting to live alongside people, but it’s not enough: study – Globalnews.ca

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Grizzly bears are doing their best to get along with people, but it still isn’t enough.

Newly published research concludes that without large wilderness areas to replenish their numbers, grizzlies would disappear from landscapes they share with humans.

“The persistence of bears near people, when we see them along highways or near towns, they’re really propped up by the fact they exist near some sort of secure wilderness,” said Clayton Lamb, a University of Alberta biologist and lead author of a paper published in the Proceedings of the National Academy of Sciences.

Read more:
Northern Alberta bear encounter captured on video

Researchers found bears in populated areas in Alberta and British Columbia have even changed how they hunt in an attempt to share living space with humans.

Story continues below advertisement

“The bears are doing what they can,” Lamb said. “The difference might have to be made up by us.”

The study set out to examine an emerging phenomenon in wildlife conservation — large carnivores re-establishing themselves on mixed landscapes including cities, highways, rural communities and patchworks of natural habitat.

It digested 41 years worth of mortality, movement and demography among 2,669 grizzlies over nearly 400,000 square kilometres of British Columbia.

It found mortality has increased steeply with the amount of human impact measured through an index that includes human population, land use, infrastructure, coastlines, roads, railroads and navigable rivers.






0:48
Grouse Mountain bears out of winter hibernation


Grouse Mountain bears out of winter hibernation

Deaths have outnumbered births and the difference is being made up through emigration of young grizzlies from nearby wilderness. For every point the index increases, a local bear population must increase the number of individuals it draws by about two per cent.

Story continues below advertisement

“Grizzly bear range is quite tied to the distance from some secure piece of wilderness,” said Lamb.

That’s despite the grizzlies’ efforts to adapt to humans. The study found young, newly arrived bears gradually learned ways to avoid contact, such as hunting and gathering at night.

Adolescent bears in areas dominated by humans have increased their nocturnal time by up to three per cent annually, which has led to corresponding increases in survival. The cost, however, is steep.






1:45
3 grizzlies spotted in Alberta woman’s backyard


3 grizzlies spotted in Alberta woman’s backyard

The scientists found it takes 14 years for a grizzly to learn how to co-exist with humans. For every bear that makes it, 29 don’t.

“A lot of those bears would have been born on a mountaintop 10 kilometres away and lived with mom in an avalanche chute and lived a normal bear life,” Lamb said.

Story continues below advertisement

“Then they find a home near town and get lured in by an apple tree. The gauntlet they have to run is very difficult.”

The study shows that high mortality has impacts far from where the deaths take place. Bears dying in mixed-used areas draws more grizzlies from the wilderness to take their place.

“Conflicts with people have rippling effects on (bear) populations far removed,” Lamb said.

Read more:
‘Never seen anything like it’: Bear cub spotted in Alberta with unique white head

Highway overpasses are one good way to reduce deaths, he suggests. But humans living with bears have to get better at removing attractants such as roadkill or fruit trees to end the bears’ constant, often fatal, migration from the wilderness.

“We’re not quite there,” said Lamb. “The system relies quite heavily on adjacent wilderness.”

Story continues below advertisement

© 2020 The Canadian Press

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Grizzly bears in the dark as they try to share living space with humans: study – Deloraine Times

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EDMONTON — Grizzly bears are doing their best to get along with people, but it still isn’t enough.

Newly published research concludes that without large wilderness areas to replenish their numbers, grizzlies would disappear from landscapes they share with humans.

article continues below

“The persistence of bears near people, when we see them along highways or near towns, they’re really propped up by the fact they exist near some sort of secure wilderness,” said Clayton Lamb, a University of Alberta biologist and lead author of a paper published in the Proceedings of the National Academy of Sciences.

Researchers found bears in populated areas in Alberta and British Columbia have even changed how they hunt in an attempt to share living space with humans.

“The bears are doing what they can,” Lamb said. “The difference might have to be made up by us.”

The study set out to examine an emerging phenomenon in wildlife conservation — large carnivores re-establishing themselves on mixed landscapes including cities, highways, rural communities and patchworks of natural habitat.

It digested 41 years worth of mortality, movement and demography among 2,669 grizzlies over nearly 400,000 square kilometres of British Columbia.

It found mortality has increased steeply with the amount of human impact measured through an index that includes human population, land use, infrastructure, coastlines, roads, railroads and navigable rivers.

Deaths have outnumbered births and the difference is being made up through emigration of young grizzlies from nearby wilderness. For every point the index increases, a local bear population must increase the number of individuals it draws by about two per cent.

“Grizzly bear range is quite tied to the distance from some secure piece of wilderness,” said Lamb.

That’s despite the grizzlies’ efforts to adapt to humans. The study found young, newly arrived bears gradually learned ways to avoid contact, such as hunting and gathering at night.

Adolescent bears in areas dominated by humans have increased their nocturnal time by up to three per cent annually, which has led to corresponding increases in survival. The cost, however, is steep.

The scientists found it takes 14 years for a grizzly to learn how to co-exist with humans. For every bear that makes it, 29 don’t.

“A lot of those bears would have been born on a mountaintop 10 kilometres away and lived with mom in an avalanche chute and lived a normal bear life,” Lamb said.

“Then they find a home near town and get lured in by an apple tree. The gauntlet they have to run is very difficult.”

The study shows that high mortality has impacts far from where the deaths take place. Bears dying in mixed-used areas draws more grizzlies from the wilderness to take their place.

“Conflicts with people have rippling effects on (bear) populations far removed,” Lamb said.

Highway overpasses are one good way to reduce deaths, he suggests. But humans living with bears have to get better at removing attractants such as roadkill or fruit trees to end the bears’ constant, often fatal, migration from the wilderness.

“We’re not quite there,” said Lamb. “The system relies quite heavily on adjacent wilderness.”

This report by The Canadian Press was first published July 7, 2020

— Follow @row1960 on Twitter

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