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.

Why Do People Toss Beads During Mardi Gras?

Kameleon007/iStock via Getty Images
Kameleon007/iStock via Getty Images

Each year, more than 1 million people descend on New Orleans for Mardi Gras, an organized parade of debauchery and alcohol-induced torpor that may be the closest thing modern civilization has to the excesses of ancient Rome. Saturating the scene on Bourbon Street are plastic beads, handed or tossed to partygoers as a kind of currency. Some bare their breasts or offer booze in exchange for the tokens; others catch them in the air and wear the layers around their necks. Roughly 25 million pounds of beads are in circulation annually, making them as much a part of the Fat Tuesday celebration as sugary cocktails and King Cake.

Traditions and rituals can be hard to pin down, but Mardi Gras historians believe the idea of distributing trinkets began in the 1870s or 1880s, several hundred years after French settlers introduced the celebration to Louisiana in the 1600s. Party organizers—known locally as krewes—handed out baubles and other shiny objects to revelers to help commemorate the occasion. Some of them threw chocolate-covered almonds. They were joined by more mischievous attendees, who threw dirt or flour on people in an effort to stir up a little bit of trouble.

Why beads? Tiny tokens that represent wealth, health, and other prosperity have been a part of human history for centuries. In Egypt, tokens were handed out in the hopes they would guarantee a happy afterlife; the abacus, or bead-based system of accounting, used trinkets to perform calculations; pagan pre-winter rituals had people throwing grains into fields hoping to appease gods that would nourish their crops.

Humans, argues archaeologist Laurie Wilkie, display "bead lust," or a penchant for shiny objects. It's one possible reason why Mardi Gras attracts so many people with their arms in the air, elated to receive a gift of cheap plastic.

Photo of a well-dressed bulldog celebrating Mardi Gras in New Orleans.
Mario Tama, Getty Images

The early beads were made of glass before more efficient production methods overseas led to an influx of plastic beads in the 1960s. Unlike some of the more organic predecessors, these beads have come under criticism for being a source of health problems and pollution. Made from petroleum, they often harbor lead that seeps into the soil and rubs off on hands. (One estimate puts the lead deposit after a Mardi Gras celebration at 4000 pounds.) In 2017, New Orleans paid $7 million in clean-up costs to remove discarded beads from drain basins. In 2018, they installed gutter guards to prevent the necklaces from getting into the system in the first place. Meanwhile, scientists have been working to create an even more eco-friendly version of the beads—like a biodegradable version made from microalgae.

Environmental hazards aside, the beads of Mardi Gras have become as much a holiday staple as Christmas stockings or Thanksgiving turkeys. But the passion and desperate need for them is only temporary; in 2018, 46 tons of the beads were removed from just five blocks of the main parade route on Charles Street. And no bacchanal should leave that much bad juju behind.

Have you got a Big Question you'd like us to answer? If so, let us know by emailing us at bigquestions@mentalfloss.com.

Why Are Shower Doors in Hotel Rooms Getting Smaller?

sl-f/iStock via Getty Images
sl-f/iStock via Getty Images

Shower doors are shrinking in posh hotels, and minimalism is to blame, Condé Nast Traveler reports.

In lieu of hanging shower curtains or providing full shower doors, many newer hotels are opting for glass panels that cover only half the length of the shower. That’s frustrating for many travelers, who complain the growing trend is inconvenient and leaves bathroom floors sopping wet and slippery after shower use.

According to Condé Nast Traveler, the half-door trend began in European hotels in the 1980s. “A lot of it comes down to people trying to design hotel rooms with limited space,” boutique hotel designer Tom Parker told the magazine. “It’s about the swing of the shower door, because it has to open outward for safety reasons, like [if] someone falls in the shower. You have to figure out where the door swing’s going to go, make sure it’s not [hitting] the main door. It’s just about clearances.” A smaller door also has the added benefit of making the space appear larger than it really is, according to the magazine.

The trend is also connected to the birth of minimalist “lifestyle hotels,” which cater to a younger, hipper clientele that gravitates toward sleek lines and modern design. Plus, half-size glass doors are easier to clean than shower curtains, which tend to trap bacteria and need to regularly be replaced, which can add up to significant additional costs for a hotel.

Theoretically, even half-door showers are designed to minimize water spillage. Designers try to level the floors in bathrooms so water doesn’t pool in random areas, and they place shower heads and knobs in areas that are more protected by glass paneling. And where design doesn’t work, hotels try to pick up the slack.

“Hotels tend to mitigate the risks by offering non-slip interior shower mats, cloth bath mats for stepping out of the shower, grab bars, [and] open showers or no-sill showers which avoid having to step up and over the ledge,” designer Douglas DeBoer, founder and CEO of Rebel Design Group, told Condé Nast Traveler.

But the half-door trend still has yet to gain much love from hotel guests. “The older generation much, much prefers having a shower door,” Parker told Condé Nast Traveler. “I’m like a 70-year-old man at heart anyway. I like [a shower door] if it’s in keeping with the style of the rest of the room.”

Have you got a Big Question you'd like us to answer? If so, let us know by emailing us at bigquestions@mentalfloss.com.

SECTIONS

arrow
LIVE SMARTER