What Caused Pangea to Break Apart?

iStock.com/alfimimnill
iStock.com/alfimimnill

Emily Devenport:

There's another way to look at this question. People tend to think in terms of supercontinents forming and then breaking up again due to convection currents in the mantle, hot material rising and causing rifts in weaker spots, possibly in old sutures where the continents were shoved together—but what is really happening is that ocean basins are opening and closing, and the ocean has an active role in subduction.

The opening and closing of an ocean basin is called a Wilson Cycle. It begins when hot material rising from the mantle stretches the overlying crust. As molten material rises, a rift is formed. The rift is widened as material continues to squeeze into it. If that rifting goes on long enough, through a broad enough swath of a continent, ocean water will eventually flow into it, and an ocean basin begins to form. The upwelling of hot material will continue to rise through that thinner area of crust, pushing the plates apart. The Atlantic Ocean is an example of a basin that is well along in the Wilson Cycle; eventually subduction is going to begin at its margins, and the whole shebang will pivot.

This will happen because at the edge of continents, sediments accumulate. The weight of those sediments, combined with the weight of the water, drives the heavier, denser edge of the oceanic plate under the continental crust, which is fatter and lighter. Eventually subduction begins, and the basin begins to close again. The Pacific Ocean is an example of a basin that's closing.

If you look at a map of the oceanic rift zones, you'll notice that the one in the Atlantic is pretty much in the middle of that ocean, but the Pacific rift zone has been pulled all the way over to North America above Central America. Subduction is actively occurring on all margins of that plate.

The simple picture is that the continents are moving toward each other across the Pacific Ocean while the Atlantic Basin continues to widen. The truth is more complicated. When plates subduct, the water in the crust lowers the melting point of those rocks, so partial melting occurs. The partially melted material begins to rise through the overlying rocks, because it's less dense, and decompression melting occurs. Eventually, the upwelling of hot material forms plutons and volcanoes above the subduction zones. Fore-arc and Back-arc [PDF] basins can form. As the oceanic crust is pulled under the continental plate, island chains and other chunky bits get sutured to the edge of the continent along with sediments, making it larger. Our world is ~4.6 billion years old, so our continents are really large, now. They're unlikely to rift through the ancient cratons that formed their hearts.

What will happen if subduction begins on the eastern side of North America before the Pacific Basin closes? The margin next to California is a transform fault; it's not subducting. Will it eventually push itself under that part of North America again, or will the transform zone get bigger? The hot spot that was driving the ancient Farallon Plate under North America was eventually overridden by the southwestern states (Arizona, New Mexico, etc.) forming a rift zone. Will it continue to rift or poop out?

There are computer models predicting what supercontinent may form next. They will continue to change as our understanding of tectonic processes gets more accurate.

This post originally appeared on Quora. Click here to view.

Who Has Jurisdiction for Crimes Committed in Space?

iStock/nedelcupaul
iStock/nedelcupaul

It's 2050. Humans have mastered commercial space travel. Hundreds of people pay thousands of dollars to be sent into orbit in a spaceship. Maybe some decide to help colonize Mars.

Then, trouble. A jilted spouse. A smuggled firearm. Perhaps a struggle followed by suffocation. A space traveler is found dead on board a ship or on the Red Planet. Who has jurisdiction over such crimes? Is there such a thing as a cosmic Hercule Poirot? Could someone fall through the cracks and get away with space murder?

To date, no one has been victim of a space crime. But because no one nation can lay claim to ownership of space, the idea of a criminal offense committed outside of our atmosphere is something people have already given some thought to.

According to NASA engineer and instructor Robert Frost, the language of law for galactic felonies would be the Outer Space Treaty of 1967. In Article VIII of the treaty, nations engaging in space exploration agree that they will bear responsibility for the actions of personnel aboard their craft. In other words, if a privatized shuttle from China sees a fight break out among crew members, leaving one injured, China would be the entity responsible for handling legal repercussions.

That varies slightly with the International Space Station, or ISS, which is home to a number of personnel from different nations. In the case of the ISS, an intergovernmental agreement signed in 1998 mandates that the home country of the offender will handle any investigation or prosecution. If the victim is a national of another country, that country will have the right to inquire as to the criminal status of the offender and seek to have jurisdiction over the matter if they feel justice isn't being meted out.

In most cases, space crime sprees would be treated the same as if an offender was traveling in a foreign country or in international waters. If you're a U.S. citizen and decide to bludgeon someone at sea or on the Moon, the various international agreements and national laws would determine how you get prosecuted. (Assuming, of course, you returned to Earth to answer the charges.)

Space crimes pose another intriguing wrinkle. In terra firma investigations, authorities can secure crime scenes, question witnesses, and preserve evidence. Aboard a spaceship or on a distant planet, these procedures would be difficult to perform, and almost impossible to do in a timely fashion. Even if a criminal investigator is on Mars, low gravity will affect blood spatter and bodies may even decay at a different rate than they do on Earth. While an American may be found liable for murder, proving it was malicious and not the result of the dangerous environment would give any prosecutor a headache. A defense attorney, on the other hand, would have a field day questioning defective spacesuits or toxic exposure to strange space chemicals.

Then again, prosecutors may not have to concern themselves with evidence. Thanks to airlocks and restrictive suits, the movement of space travelers is highly monitored. It would be hard to make any plausible deniability about one's whereabouts.

The closest thing to space crime that law enforcement has yet encountered may be crimes committed in Antarctica, the frigid and isolated continent that's unaffiliated with any country but operates under the Antarctic Treaty signed by 54 nations. The agreement declares that the suspect is likely under their home country's jurisdiction. In some cases, the country owning the research station where the alleged crime took place steps in. In 2018, a Russian researcher at Bellingshausen Station on King George Island went after his victim with a knife in the station's dining room. He was charged in Russia, though reports indicate the case has since been dropped. And in 2000, an Australian astrophysicist suspected of being fatally poisoned had an autopsy performed in New Zealand. The exam showed he had ingested methanol, but it remains unknown whether he did so accidentally or whether someone gave it to him. New Zealand police were unable to determine the source.

A person committing murder in space would certainly be held responsible. But whether they'd ever be found guilty beyond a reasonable doubt remains very much up in—and beyond—the air.

Why Do Dogs Eat Grass?

iStock/K_Thalhofer
iStock/K_Thalhofer

If something is edible (or even if it's not), many dogs will gladly make a meal of it. But if you see your pet grazing on your front lawn like cattle, it may be driven by something more than its undiscerning appetite. Eating grass frantically can be a sign that a dog is sick.

It's not unusual to see a dog vomit after consuming grass, prompting some pet owners to wonder if their dog ate the grass to soothe its own upset stomach or if the grass is what caused its symptoms in the first place. According Dr. Jerry Klein, chief veterinary officer for the American Kennel Club, this behavior is sometimes a response to symptoms that were already present. "When dogs go outside and gobble grass really quickly, there's usually a reason, an instinctual behavior to try to induce some kind of gastrointestinal reaction," he tells Mental Floss. "When they realize they're nauseous or something else, the only thing they know how to do is to force themselves to vomit. Some dogs that eat grass chomp it down without really chewing it, and often times may vomit something up and that's how they treat themselves."

Despite it being a common issue for pet owners, little research has been done into why dogs eat grass. It's likely that stomach problems only explain this behavior part of the time. In other situations, a dog may eat grass for the same reason it eats your shoes or the groceries you left on the kitchen counter: Because it's hungry, anxious, or bored.

So how can you tell when your dog is munching grass for pleasure and when it's trying to induce itself to vomit? Pay attention to the way it eats. Dogs are omnivorous, meaning they eat both plants and animals, so just eating grass alone normally won't be enough to make it sick. But if a dog is gorging on grass faster than it can chew it, that may be an indication that something is wrong. Whole blades of grass can irritate a dog's throat and stomach lining, potentially causing them to throw up if they swallow a lot of them in a short amount of time.

No matter the reason for your dog's grass-eating habits, Klein says that they aren't a major issue. The behavior shouldn't be encouraged, as grass in public places can potentially carry harmful chemicals like pesticides, so stop your dog if you see it grazing. But if it shows no signs of illness or discomfort afterward, there's no need to rush it to the vet. "If I see a dog eating grass, I'm not going to panic. I would try to stop it and then monitor it to see how it acts in the next 15 to 20 minutes. Look at how the dog's acting, its body shape and movement, and the feeling you get from the dog."

One condition related to vomiting that would warrant a trip to the vet is something called bloat. This happens when a dog's stomach fills with air, causing it to retch without actually throwing anything up. This is a medical emergency and can be deadly if left untreated.

A dog who vomits after eating grass and looks happy afterward, on the other hand, is probably not a cause for concern—though you may argue otherwise when you're steam-cleaning your carpet.

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