The Earth’s crust is what we live on and is by far the thinnest layers of Earth. The thickness varies depending on where you are on Earth, with the oceanic crust being 5-10 km and continental mountain ranges being up to 30-45 km thick.
But what happens below this crust remains obscure, 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 found some significant clues about where those rocks have been hiding.
A new study has come out with fresh evidence that while most of the Earth’s crust is relatively new, a small percentage is made up of ancient chunks that had sunk long ago back into the mantle then later resurfaced. They also found that based on the amount of that “recycled” crust, that the planet had been churning out crust consistently since its formation 4.5 billion years ago—a picture that contradicts prevailing theories.
Co-author Munir Humayun, a MagLab geochemist and professor at Florida State’s Department of Earth, Ocean, and Atmospheric Science (EOAS) said, “Like salmon returning to their spawning grounds, some oceanic crust returns to its breeding ground, the volcanic ridges where the fresh crust is born. We used a new technique to show that this process is essentially a closed-loop and that recycled crust is distributed unevenly along ridges.”
Scientists have long estimated about what happens to subducted crust after being reabsorbed into the hot, high-pressure environment of the planet’s mantle. It may sink further into the mantle and settle there, or ascend back to the surface in tufts, or to the surface in plumes, or swirl through the mantle.
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 highlight the mystery of the disappearing crust, scientists observed 500 samples of basalt collected from 30 regions of ocean ridges. Some were enriched, some were depleted, and some were in between.
Scientists discovered that the overall extents of germanium and silicon were lower in melts of the recycled crust than in the “virgin” basalt rising out of melted mantle rock. So they built up another strategy that pre-owned that proportion to distinguish a particular chemical fingerprint for the subducted crust.
They thus devised an accurate technique to measure the 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.
Scientists first discovered nothing. This concerned scientists, and they started looking at the problem from a wider view. Instead of comparing the basalts of different regions, they compared enriched and depleted basalts.
After quickly re-crunching the data, scientists were thrilled to see apparent differences among those groups of basalts.
The team had detected lower germanium-to-silicon ratios in enriched basalts—the chemical fingerprint for the 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.
Humayun said, “Sometimes you’re looking too closely, with your nose in the data, and you can’t see the patterns. 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. This figure 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.”
- Elemental constraints on the amount of recycled crust in the generation of mid-oceanic ridge basalts (MORBs)” Science Advances (2020). DOI: /10.1126/sciadv.aba2923
White-throated sparrows have changed their tune, BC study unveils – Terrace Standard
White-throated sparrows are changing their tune — an unprecedented development scientists say has caused them to sit up and take note.
Ken Otter, a biology professor at the University of Northern British Columbia, whose paper on the phenomenon was published on Thursday, said most bird species are slow to change their songs, preferring to stick with tried-and-true tunes to defend territories and attract females.
But the shift to this new tune went viral across Canada, travelling over 3,000 kilometres between 2000 and 2019 and wiping out a historic song ending in the process, he said.
“The song is always described as being ‘Oh My Sweet Canada Canada Canada Canada — so that Canada is three syllables. It’s a da-da-da, da-da-da, da-da-da, da-da-da sound. That’s the traditional description of the song going back into early 1900s,” Otter said in an interview Wednesday.
But now, the song has changed.
“The doublet sounds like Oh My Sweet Cana-Cana-Cana-da. They are stuttering and repeating the first two syllables and they are doing it very rapidly. It sounds very different.”
From British Columbia to central Ontario, these native birds have ditched their traditional three-note-ending song for a two-note-ending variant, he said, adding researchers still don’t know what has made the new tune so compelling.
Otter drew a comparison to people picking up the accent, phrases and pneumonics of a new area they move into.
“This is actually the opposite,” he said.
Male sparrows are showing up singing atypical songs but then others are starting to adopt that, and over time the dialect is actually changing within that site to the new type and replacing the old tune, he said.
“So it’s like somebody from Australia arriving in Toronto and people saying, ‘hey, that sounds really cool,’ mimicking an Australian accent and then after 10 years everybody in Toronto has an Australian accent,” he said.
“That’s why, at least within the scientific community, it’s getting so much interest. It is completely atypical to what you would predict around all the theories that you have about dialects.”
Otter and a team of citizen scientists have found that the new tune is not just more popular west of the Rocky Mountains, but was also spreading rapidly across Canada.
“Originally, we measured the dialect boundaries in 2004 and it stopped about halfway through Alberta,” he said in a news release.
“By 2014, every bird we recorded in Alberta was singing this western dialect, and we started to see it appearing in populations as far away as Ontario, which is 3,000 kilometres from us.”
The scientists predicted that the sparrows’ overwintering grounds were playing a role in the rapid spread of the two-note ending, he said.
Scientists believed that juvenile males may be able to pick up new song types if they overwinter with birds from other dialect areas, and take them to new locations when they return to breeding grounds, which could explain the spread, he said.
So they fitted the birds with geolocators — what Otter called “tiny backpacks” — to see if western sparrows that knew the new song might share overwintering grounds with eastern populations that would later adopt it.
“They found that they did,” he said in the release.
Otter said he does not know what has caused the change, and his team found that the new song didn’t give male birds a territorial advantage over others.
“In many previous studies, the females tend to prefer whatever the local song type is,” he said.
“But in white-throated sparrows, we might find a situation in which the females actually like songs that aren’t typical in their environment. If that’s the case, there’s a big advantage to any male who can sing a new song type.”
The new song can be chalked up to evolution, he said in the interview.
Otter said he prefers the two-note song because it sounds smoother.
“But I’m not a sparrow so it doesn’t really matter which one I prefer,” he said with a laugh.
But the tune may be continuing to change, he said adding scientists were supposed to study it this year but COVID-19 has put a damper on the field season.
“The two note is not the be all and end all because in the last five years we noticed a male that was singing something slightly different than the standard two note doublet song,” Otter said.
“And when we recorded it we noticed he was modifying the amplitude of the first note. And more of them are doing it now. We could be seeing waves of these things that we just never noticed before.”
Hina Alam, The Canadian Press
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Full buck moon with a lunar eclipse visible this weekend – BC News – Castanet.net
British Columbians were treated to a glorious full Strawberry Moon this June, but they’ll have the opportunity to view a magnificent full Buck Moon this July in addition to a lunar eclipse.
Named after the time of year when young bucks begin to grow new antlers from their foreheads, the July full moon marks a time of renewal. The full Buck Moon will be at its fullest on July 4.
As the full moon increases in fullness, British Columbians will also be able to view a “penumbral lunar eclipse.” Timeanddate.com explains is set to begin July 4 at 8:07 p.m. but that it won’t be directly visible at that time.
At 9:22 p.m., “it will be rising but the the combination of a very low moon and the total eclipse phase will make the moon so dim that it will be extremely difficult to view until moon gets higher in the sky or the total phase ends.”
The moon will be closest to the centre of shadow at 9:29 p.m. (-0.644 Magnitude). It will end at 10:52 p.m.
During this penumbral lunar eclipse, the Earth’s main shadow does not cover the Moon.
How to watch the Fourth of July weekend's "buck moon" lunar eclipse – CBS News
Fourth of July celebrations look a little bit different this year due to the coronavirus pandemic, but skywatchers are still in for a special Independence Day treat. The weekend brings not only a full moon, but also a lunar eclipse.
The “buck moon” lunar eclipse will be visible the night of July 4 into the morning of July 5. Viewers across most of North and South America, as well as parts of southwestern Europe and Africa, will be able to spot the celestial phenomenon.
The event will be a penumbral eclipse, not a total lunar eclipse, meaning part of the moon will pass through the outer part of Earth’s shadow.
According to The Old Farmer’s Almanac, July’s full moon is called the “buck moon,” because early summer is when male deer grow new antlers. It’s also called the thunder moon — because of summer storms that occur in July — the guru moon and the hay moon.
According to NASA, the full moon will peak early Sunday morning, at 12:30 a.m. EDT. At that time, about 35% of the moon will be in the partial shadow.
The full moon peaks just a few minutes later, appearing opposite the sun at 12:44 a.m. EDT. However, it will appear full all weekend, from Friday evening into Monday morning.
Clear skies will reveal the moon in all its glory, but moon gazers may need the help of a telescope or binoculars for the full effect. It’s also possible the events could be overshadowed by Fourth of July fireworks across the U.S. — despitefrom officials.
Not only does the Fourth of July weekend mark a full moon and lunar eclipse, it also highlights the closest grouping of Saturn, Jupiter and the moon, forming a triangle of celestial celebration.
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