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.

Where Did the Term Brownie Points Come From?

bhofack2/iStock via Getty Images
bhofack2/iStock via Getty Images

In a Los Angeles Times column published on March 15, 1951, writer Marvin Miles observed a peculiar phrase spreading throughout his circle of friends and the social scene at large. While standing in an elevator, he overheard the man next to him lamenting “lost brownie points.” Later, in a bar, a friend of Miles's who had stayed out too late said he would never “catch up” on his brownie points.

Miles was perplexed. “What esoteric cult was this that immersed men in pixie mathematics?” he wrote. It was, his colleagues explained, a way of keeping “score” with their spouses, of tallying the goodwill they had accrued with the “little woman.”

Over the decades, the phrase brownie points has become synonymous with currying favor, often with authority figures such as teachers or employers. So where exactly did the term come from, and what happens when you “earn” them?

The most pervasive explanation is that the phrase originated with the Brownies, a subsect of the Girl Scouts who were encouraged to perform good deeds in their communities. The Brownies were often too young to be official Girl Scouts and were sometimes the siblings of older members. Originally called Rosebuds in the UK, they were renamed Brownies when the first troops were being organized in 1916. Sir Robert Baden-Powell, who had formed the Boy Scouts and was asked to name this new Girl Scout division, dubbed them Brownies after the magical creatures of Scottish folklore that materialized to selflessly help with household chores.

But the Brownies are not the only potential source. In the 1930s, kids who signed up to deliver magazines like The Saturday Evening Post and Ladies' Home Journal from Curtis Publishing were eligible for vouchers labeled greenies and brownies that they could redeem for merchandise. They were not explicitly dubbed brownie points, but it’s not hard to imagine kids applying a points system to the brownies they earned.

The term could also have been the result of wartime rationing in the 1940s, where red and brown ration points could be redeemed for meats.

The phrase didn’t really seem to pick up steam until Miles's column was published. In this context, the married men speaking to Miles believed brownie points could be collected by husbands who remembered birthdays and anniversaries, stopped to pick up the dry cleaning, mailed letters, and didn’t spend long nights in pubs speaking to newspaper columnists. The goal, these husbands explained, was never to get ahead; they merely wanted to be considered somewhat respectable in the eyes of their wives.

Later, possibly as a result of its usage in print, grade school students took the phrase to mean an unnecessary devotion to teachers in order to win them over. At a family and faculty meeting at Leon High in Tallahassee, Florida, in 1956, earning brownie points was said to be a serious problem. Also called apple polishing, it prompted other students in class to shame their peers for being friendly to teachers. As a result, some were “reluctant to be civil” for fear they would be harassed for sucking up.

In the decades since that time, the idiom has become attached to any act where goodwill can be expected in return, particularly if it’s from someone in a position to reward the act with good grades or a promotion. As for Miles: the columnist declared his understanding of brownie points came only after a long night of investigation. Arriving home late, he said, rendered him “pointless.”

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Grocery Stores vs. Supermarkets: What’s the Difference?

gpointstudio/iStock via Getty Images
gpointstudio/iStock via Getty Images

These days, people across the country are constantly engaging in regional term debates like soda versus pop and fireflies versus lightning bugs. Since these inconsistencies are so common, you might have thought the only difference between a grocery store and a supermarket was whether the person who mentioned one was from Ohio or Texas. In reality, there are distinctions between the stores themselves.

To start, grocery stores have been around for much longer than supermarkets. Back when every town had a bakery, a butcher shop, a greengrocery, and more, the grocery store offered townspeople an efficient shopping experience with myriad food products in one place. John Stranger, vice president group supervisor of the food-related creative agency EvansHardy+Young, explained to Reader’s Digest that the grocer would usually collect the goods for the patron, too. This process might sound familiar if you’ve watched old films or television shows, in which characters often just hand over their shopping lists to the person behind the counter. While our grocery store runs may not be quite so personal today, the contents of grocery stores remain relatively similar: Food, drinks, and some household products.

Supermarkets, on the other hand, have taken the idea of a one-stop shop to another level, carrying a much more expansive array of foodstuffs as well as home goods, clothing, baby products, and even appliances. This is where it gets a little tricky—because supermarkets carry many of the same products as superstores, the next biggest fish in the food store chain, which are also sometimes referred to as hypermarkets.

According to The Houston Chronicle, supermarkets and superstores both order inventory in bulk and usually belong to large chains, whereas grocery stores order products on an as-needed basis and are often independently owned. Superstores, however, are significantly larger than either grocery stores or supermarkets, and they typically look more like warehouses. It’s not an exact science, and some people might have conflicting opinions about how to categorize specific stores. For example, Walmart has a line of Walmart Neighborhood Markets, which its website describes as “smaller-footprint option[s] for communities in need of a pharmacy, affordable groceries, and merchandise.” They’re not independently owned, but they do sound like grocery stores, especially compared to Walmart’s everything-under-the-sun superstore model.

Knowing the correct store terms might not always matter in casual conversation, but it could affect your credit card rewards earnings. American Express, for example, offers additional rewards on supermarket purchases, and it has a specific list of stores that qualify as supermarkets, including Gristedes, Shoprite, Stop & Shop, and Whole Foods. Target and Walmart, on the other hand, are both considered superstores, so you won’t earn bonuses on those purchases.

And, since grocery shopping at any type of store can sometimes seem like a competitive sport, here’s the ideal time to go.

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