Connect with us

Science

Earth has been recycling crust for most of its history

Published

on

June 26 (UPI) — New research suggests roughly 5 to 6 percent of the Earth’s mantle is made up of recycled crust.

The discovery, detailed Friday in the journal Science Advances, suggests Earth has been producing new crust at a similar rate for most of the planet’s history.

Geologists knew that some of Earth’s crust regularly sinks back into the mantle, but until now, they weren’t sure how much gets recycled — a key to understanding the history of crustal formation and subduction.

To better understand the trajectory of crust that gets swallowed back into the mantle, scientists collected 500 samples of basalt from mid-ocean ridges all over the world.

“The chemical composition of oceanic basalt — Mid-Oceanic Ridge Basalt, or MORB — that erupted along the 40,000-kilometer long oceanic ridge system is systematically depleted in elements — termed incompatible elements — that are concentrated in the continental crust: elements like potassium, thorium, uranium and lead,” study co-author Munir Humayun told UPI in an email.

What has long perplexed scientists is that MORB comes in three flavors, each with different concentrations of incompatible elements.

“Normal MORB is depleted to an extent sufficient to explain extraction of the continental crust from the mantle, but there are basalts that are more depleted than Normal MORB (depleted-MORB) and basalts that are more enriched than Normal-MORB (enriched-MORB), and both are present in significant abundances,” Humayun, a professor and geochemist at the Florida State University-headquartered National High Magnetic Field Laboratory, said.

Until now, researchers weren’t sure what accounted for the differences in the amounts of incompatible elements found in basalt. Scientists surmised that recycled crust might help explain the formation of the three types of basalt.

“Recycled oceanic crust that melts at ridges produces melts that are lower in the ratio of the element germanium (Ge) to the element silicon (Si), two elements that are geochemically very similar in their behavior during melting,” Humayun said.

“We developed a way of measuring small variations in the Ge/Si ratio and used this to show that enriched basalts have lower Ge/Si ratios consistent with the addition of melts from subducted recycled crust,” he said.

Researchers found that lower Ge/Si ratios were present in enriched basalts from all of the 30 different regions — scattered across the globe — from which the samples were sourced. This, they say, is evidence of a globally and historically consistent rate of crust recycling.

Many scientists have hypothesized that the crust that gets pulled back into the mantle sinks deep into the mantle’s bottom layers and remains there — with only small plumes floating back toward the upper mantle.

Others have estimated that recycled crust gets evenly distributed throughout the mantle, like a chocolate swirl in a vanilla cake — the “marble cake” theory.

The latest findings support the latter theory. The findings have implications for the history of crustal formation and subduction.

“We were most surprised to confirm the theory of professor Alex Sobolev of the University of Grenoble that the mantle under ridges has an average of about 5 percent recycled crust,” Humayun said.

“It could only have that much recycled crust if the vigor of subduction has been similar throughout most of Earth’s history and that most of the recycled crust is not ponded in ‘subduction graveyards’ at the bottom of the mantle,” he said.



Source link

Science

Moon’s smallest shadows may be hiding tiny patches of water ice

Published

on

Oct. 26 (UPI) — Water ice may be more abundant on the moon’s surface than previously thought.

New research, published Monday in the journal Nature Astronomy, suggests tiny patches of ice may be hiding inside lunar shadows as a small as a penny.

“If you can imagine standing on the surface of the moon near one of its poles, you would see shadows all over the place,” Paul Hayne, an assistant professor of astrophysical and planetary sciences at the University of Colorado, said in a news release. “Many of those tiny shadows could be full of ice.”

Hayne and his colleagues suggest many of the moon’s smallest shadows are permanent. Scientists predict many of these darkened pockets of the lunar surface, or “cold traps,” haven’t been hit with a ray of sunlight in billions of years.

“If we’re right, water is going to be more accessible for drinking water, for rocket fuel, everything that NASA needs water for,” said Hayne.

For a bigger example of a cold trap, the study’s authors looked to Shackleton Crater, a massive depression on the moon’s southern pole. Because much of crater remains permanently darkened, temperatures inside the 13-mile-wide depression remain a steady minus 300 degrees Fahrenheit all year long.

“The temperatures are so low in cold traps that ice would behave like a rock,” Hayne said. “If water gets in there, it’s not going anywhere for a billion years.”

To see how common cold traps are, researchers collected a wealth of data on the contours of the lunar surface and used models to simulate what the moon looks like at small scales. Their analysis showed the lunar surface is a lot like a golf ball, covered in tiny dimples.

The models showed many of these tiny bumps, ridges and crests are capable of keeping small portions of the lunar surface in permanent shadow. Though simulations suggest most of the moon’s cold traps measure no more than a centimeter wide, they combine to create 7,000 square miles of permanent shadow.

Scientists can’t be sure that these tiny cold traps hold water ice. To find out, a lunar mission will be necessary.

The finding was announced the same day NASA confirmed water molecules on the sunlit surface of the moon.

The discovery, researchers said, needs to be confirmed — the atmosphere of the moon is so thin that water molecules should be quickly lost to space, so how they would remain on the surface is unknown.

But finding water resources will be essential to establishing a human presence on the moon, they said.

If the cold traps identified by Hayne and his colleagues do indeed hold water, and water molecules are found across the sunlit side of the moon, NASA may have more flexibility in where they can base their human missions.



Source link

Continue Reading

Science

Accessible healthcare could help slow climate change, reverse biodiversity losses

Published

on

Oct. 26 (UPI) — To protect forests and vulnerable ecosystems, erect healthcare clinics. That’s what nonprofit organizers did in Indonesia, where deforestation rates in neighboring Gunung Palung National Park declined dramatically during the first 10 years of the clinic’s operation.

The affordable healthcare clinic was set up in 2007 by a pair of nonprofits, Alam Sehat Lestari and Health In Harmony. Prior to the arrival of the clinic, the forests of Gunung Palung were shrinking annually as a result of uncontrolled illegal logging.

To curb the losses, the clinic offered discounted services to villages that enacted community-wide logging reductions and other conservation-minded reforms.

Researchers described the clinic’s environmental and public health successes in a new paper, published Monday in the journal PNAS.

“This innovative model has clear global health implications,” study co-author Michele Barry, senior associate dean of global health at Stanford University and director of the Center for Innovation in Global Health, said in a news release. “Health and climate can and should be addressed in unison, and done in coordination with and respect for local communities.”

In addition to offering community-wide discounts pegged to reductions in logging, the clinic also provided healthcare services for barter, allowing villagers to pay with tree seedlings, handicrafts and labor.

Health data collected by the clinic revealed a significant drop in infectious and non-communicable diseases between 2007 and 2017. Satellite data showed that deforestation rates in the forests surrounding the clinic and villages receiving service declined 70 percent compared to control plots far from the clinic.

“We didn’t know what to expect when we started evaluating the program’s health and conservation impacts, but were continually amazed that the data suggested such a strong link between improvements in health care access and tropical forest conservation,” said lead study author Isabel Jones, recent recipient of a doctoral degree in biology from Stanford.

Researchers found that the biggest reductions in logging occurred surrounding the villages that used the healthcare clinic the most.

More than a third of protected forests around the globe are either owned, managed, used or occupied by indigenous groups and local communities, but conservation planning and regulatory decision rarely involves input from these communities.

The opposite was true in West Kalimantan, Indonesia, where nonprofit leaders met regularly with local villages to come up with a strategy for protecting the environment while also meeting the region’s public health needs.

Researchers suggest the clinic’s success can serve as a model for conservation and public health initiatives all over the world.

“The data support two important conclusions: human health is integral to the conservation of nature and vice versa, and we need to listen to the guidance of rainforest communities who know best how to live in balance with their forests,” said Monica Nirmala, the executive director of the clinic from 2014 to 2018 and current board member of Health In Harmony.



Source link

Continue Reading

Science

Space companies use Earth-imaging satellites to combat climate change

Published

on

The SpaceX Crew Dragon spacecraft carrying four astronauts is pictured approaching the International Space Station for docking on November 16, 2020. The trip from NASA’s Kennedy Space Center in Florida took 27 and a half hours. Photo courtesy of NASA | License Photo



Source link

Continue Reading

Trending