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.

What's the Difference Between Memorial Day and Veterans Day?

iStock/flySnow
iStock/flySnow

It may not be easy for some people to admit, but certain national holidays often get a little muddled—namely, Memorial Day and Veterans Day. In fact, the U.S. Department of Veterans Affairs sees the confusion often enough that they spelled out the distinction on their website. The two days are held six months apart: Veterans Day is celebrated every November 11, and Memorial Day takes place on the last Monday of May as part of a three-day weekend with parades and plenty of retail sales promotions. You probably realize both are intended to acknowledge the contributions of those who have served in the United States military, but you may not recall the important distinction between the two. So what's the difference?

Veterans Day was originally known as Armistice Day. It was first observed on November 11, 1919, the one-year anniversary of the end of World War I. Congress passed a resolution making it an annual observance in 1926. It became a national holiday in 1938. In 1954, President Dwight D. Eisenhower changed the name from Armistice Day to Veterans Day to recognize veterans of the two world wars. The intention is to celebrate all military veterans, living or dead, who have served the country, with an emphasis on thanking those in our lives who have spent time in uniform.

We also celebrate military veterans on Memorial Day, but the mood is more somber. The occasion is reserved for those who died while serving their country. The day was first observed in the wake of the Civil War, where local communities organized tributes around the gravesites of fallen soldiers. The observation was originally called Decoration Day because the graves were adorned with flowers. It was held May 30 because that date wasn't the anniversary for any battle in particular and all soldiers could be honored. (The date was recognized by northern states, with southern states choosing different days.) After World War I, the day shifted from remembering the fallen in the Civil War to those who had perished in all of America's conflicts. It gradually became known as Memorial Day and was declared a federal holiday and moved to the last Monday in May to organize a three-day weekend beginning in 1971.

The easiest way to think of the two holidays is to consider Veterans Day a time to shake the hand of a veteran who stood up for our freedoms. Memorial Day is a time to remember and honor those who are no longer around to receive your gratitude personally.

Have you got a Big Question you'd like us to answer? If so, send it to bigquestions@mentalfloss.com.

What Is the Kitchen Like on the International Space Station?

iStock/Elen11
iStock/Elen11

Clayton C. Anderson:

The International Space Station (ISS) does not really have a "kitchen" as many of us here on Earth might relate to. But, there is an area called the "galley" which serves the purpose of allowing for food preparation and consumption. I believe the term "galley" comes from the military, and it was used specifically in the space shuttle program. I guess it carried over to the ISS.

The Russian segment had the ONLY galley when I flew in 2007. There was a table for three, and the galley consisted of a water system—allowing us to hydrate our food packages (as needed) with warm (tepid) or hot (extremely) water—and a food warmer. The food warmer designed by the Russians was strictly used for their cans of food (about the size of a can of cat food in America). The U.S. developed a second food warmer (shaped like a briefcase) that we could use to heat the more "flexibly packaged" foodstuffs (packets) sent from America.

Later in the ISS lifetime, a second galley area was provided in the U.S. segment. It is positioned in Node 1 (Unity) and a table is also available there for the astronauts' dining pleasures. Apparently, it was added because of the increasing crew size experienced these days (6), to have more options. During my brief visit to ISS in 2010 (12 days or so) as a Discovery crewmember, I found the mealtimes to be much more segregated than when I spent five months on board. The Russians ate in the Russian segment. The shuttle astronauts ate in the shuttle. The U.S. ISS astronauts ate in Node 1, but often at totally different times. While we did have a combined dinner in Node 1 during STS-131 (with the Expedition 23 crew), this is one of the perceived negatives of the "multiple-galley" scenario. My long duration stint on ISS was highlighted by the fact that Fyodor Yurchikhin, Oleg Kotov, and I had every single meal together. The fellowship we—or at least I—experienced during those meals is something I will never, ever forget. We laughed, we argued, we celebrated, we mourned …, all around our zero-gravity "dinner table." Awesome stuff!

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

Clayton "Astro Clay" Anderson is an astronaut, motivational speaker, author, and STEAM education advocate.

His award-winning book The Ordinary Spaceman, Astronaut Edition Fisher Space Pen, and new children's books A is for Astronaut; Blasting Through the Alphabet and It's a Question of Space: An Ordinary Astronaut's Answers to Sometimes Extraordinary Questions are available at www.AstroClay.com. For speaking events www.AstronautClayAnderson.com. Follow @Astro_Clay #WeBelieveInAstronauts

SECTIONS

arrow
LIVE SMARTER