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Head-on Collision With Another Planet Formed Earth and Moon

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Our galactic neighborhood is pretty peaceful these days. So peaceful, in fact, that it’s easy to forget its violent and spectacular beginnings. Fortunately, we have scientists to remind us. A paper published last week in the journal Science reports that Earth once smashed into, then mixed with, another planet. They say the Moon formed out of the resulting wreckage too.

That planet’s name was Theia. At the time of the collision, Theia was so young that researchers refer to it as a “planetary embryo.” Though it's important to note that Earth was only 100 million years old itself—also young in cosmic time.

While knowledge of the planets’ collision isn't new, the paper's co-authors uncovered new details of the event. Most scientists believed the impact had occurred at a 45-degree angle, like one car sideswiping another. But this new research shows it was probably more like a brutal head-on collision. 

How can you be sure about something that happened to our planet nearly 4.5 billion years ago? Take a good look at the Moon. Researchers tested lunar rock samples collected by astronauts on the Apollo 12, 15, and 17 missions. They also looked at six volcanic rocks from Hawaii and Arizona. The scientists focused on the rocks’ chemical makeup—specifically on their oxygen atoms.

Researchers Paul Warren, Edward Young and Issaku Kohl with a moon rock sample. Image Credit: Christelle Snow/UCLA

There are several isotopes of oxygen, each named for its number of protons and neutrons. O-16, which makes up nearly all of the oxygen on Earth (including in rocks), has eight protons and eight neutrons. We also have small quantities of O-17 and O-18. The ratio of these three isotopes acts as a chemical signature, so if two entities have the same ratio, it’s likely they’re made of the same stuff.

The theory was that Theia’s hit-and-run impact flung shards of both planets outward into space, where gravitational forces compressed them into a single ball: the Moon. If that’s so, then the Moon’s ratio of isotopes should look different from Earth’s. And some scientists believe that’s the case.

But the researchers behind the new paper argue otherwise. "We don't see any difference between the Earth's and the moon's oxygen isotopes; they're indistinguishable," lead author Edward Young said in a press release

What does this mean? It means, the researchers say, that Theia hit Earth hard and fast, and likely straight-on. Some of the debris from Theia and Earth combined to form the planet we call home today, and some of it combined to form the Moon. 

"Theia was thoroughly mixed into both the Earth and the Moon, and evenly dispersed between them," Young said. "This explains why we don't see a different signature of Theia in the Moon versus the Earth."

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Here's What You Need to Know Before Getting Inked or Pierced, According to Doctors
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Getting inked or pierced is a rite of passage for many teens and young adults. But before getting that belly ring or butterfly on your back, experts want you to be aware of the risks, which are reviewed in a new clinical report from the American Academy of Pediatrics (AAP). According to NPR, it's the first set of recommendations the professional association has ever released on the practices.

Forthcoming in the October 2017 issue of Pediatrics and available online, the report provides a general assessment of the types and methods used to perform body modifications, along with potential health and social consequences. Here are a few main takeaways:

—It's unclear how often tattoos cause health complications, but they're generally believed to be rare, with the greatest risk being infection. One recent study found that nanoparticles in ink can travel to and linger in lymph nodes for an extended period. That said, you should check with your doctor to make sure all of your immunizations are up to date before getting either a tattoo or piercing, and that you're not taking any immunity-compromising medicines.

—Before shelling out your hard-earned cash on a tattoo, make sure it's something you'll likely still appreciate in five to 10 years, as it costs anywhere from $49 to $300 per square inch to remove a tattoo with lasers. (This might provide all the more incentive to opt for a small design instead of a full sleeve.)

—About half of people 18 to 29 years of age have some kind of piercing or tattoo, according to Dr. Cora Breuner, who is chair of the AAP committee on adolescence. Many individuals don't regret getting one, with some reporting that tattoos make them feel sexier. But while millennials appear to be cool with metal and ink, hiring managers might not be too pleased: In a 2014 survey of 2700 people, 76 percent said they thought a tattoo or piercing had hindered their chances of getting hired, and nearly 40 percent thought tattooed employees reflected poorly on their employers.

—Not all tattoo parlors are created equal, as each state has different regulations. Keep a close eye on whether your artist uses fresh disposable gloves, fresh needles, and unused ink poured into a new container. This helps prevent infection.

—The advice is similar for getting pierced: Make sure the piercer puts on new, disposable gloves and uses new equipment from a sterile container. Tongue piercings can cause tooth chippings, so be careful of that—and remove any piercings before you play contacts sports.

The full report is available online.

[h/t NPR]

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The Body
7 Essential Facts About the Pelvis
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The human body is an amazing thing. For each one of us, it’s the most intimate object we know. And yet most of us don’t know enough about it: its features, functions, quirks, and mysteries. Our series The Body explores human anatomy, part by part. Think of it as a mini digital encyclopedia with a dose of wow.

The pelvis, which crooner Elvis was famous for thrusting around in ways that raised eyebrows, is not actually a single body part but a term that refers to a collection of bones, muscles and organs below the waist. We spoke to Katherine Gillogley, department chair of obstetrics and gynecology with Mercy Medical Group in Sacramento, California, for these seven facts about the pelvis.

1. SO WHAT IS THE PELVIS, EXACTLY?

"The pelvis refers to the lower abdominal area in both men and women," Gillogley says. "An important function of the pelvis region is to protect organs used for digestion and reproduction, though all its functions are crucial," she says. It protects the bladder, both large and small intestines, and male and female reproductive organs. Another key role is to support the hip joints.

2. THE PELVIC BONES FORM A BASIN.

Four bones come together to form a bowl-like shape, or basin: the two hip bones, the sacrum (the triangle-shaped bone at the low back) and the coccyx (also known as the tailbone).

3. YOUR PELVIC FLOOR IS LIKE A TRAMPOLINE.

At the bottom of the pelvis lies your pelvic floor. You don't have to worry about sweeping it, but you might want to do Kegel exercises to keep it strong. The pelvic floor is like a "mini-trampoline made of firm muscle," according the Continence Foundation of Australia. Just like a trampoline, the pelvic floor is flexible and can move up and down. It also creates a surface (floor) for the pelvic organs to lie upon: the bladder, uterus, and bowels. It has holes, too, for vagina, urethra, and anus to pass through.

4. IT PLAYS A KEY PART IN WALKING.

Anyone who has ever broken a pelvic bone or pulled a pelvic muscle will know just how key a role the pelvis plays in such functions as walking and standing. "The pelvis also acts as a solid foundation for the attachment of the spinal column and legs," says Gillogley.

5. THE FEMALE PELVIS STARTS OUT LARGER, BUT NARROWS OVER TIME.

Gillogley says that the female pelvis "tends to be larger and wider" than the male, most likely to accommodate a baby during pregnancy and to make childbirth possible. However, women's pelvises narrow as they age, suggesting that they start out wider to accommodate childbearing and then shift when that is no longer necessary. A shifting pelvis shape is thought to be a key part of our evolutionary history, as it changed as when we began walking upright.    

6. PREGNANCY CHANGES THE PELVIS FOREVER.

During pregnancy the body secretes a hormone known as relaxin to help the body accommodate the growing baby and soften the cervix. However, what happens is, "the joints between the pelvic bones actually loosen and slightly separate during pregnancy and childbirth," Gillogley says. Sometimes, however, relaxin can make the joints too loose, causing a painful syndrome known as symphysis pubis dysfunction (SPD), causing the pelvic joint to become unstable, causing pain and weakness in the pelvis, perineum and even upper thighs during walking and other activities. Many women with the condition have to wear a pelvic belt. It usually resolves after pregnancy is over, though physical therapy may be necessary.

7. IT'S ACCIDENT PRONE.

According to the American Association for the Surgery of Trauma, about 8 to 9 percent of blunt trauma includes pelvic injury, Gillogley says. "These accidents include falls, motor vehicle crashes, bicycle accidents, and pedestrians being struck by moving vehicles. With these serious injuries, pelvic bones can fracture or dislocate and sometimes bladder injury even occurs." So take care with your pelvis—in worse-case scenarios, breaks of the pelvic bones can require pins, rods, and surgery to fix.

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