Scientists Find We're Pooping Out Plastic

Unless you’re very ill, it’s not likely anyone will be analyzing your poop under a microscope anytime soon. But if someone did, you might be surprised that among the assorted bacteria and waste lurks something a little more disconcerting: traces of plastic.

The disturbing revelation that humans are internalizing plastic material was announced this week at the United European Gastroenterology conference in Vienna. Researchers at the Medical University of Vienna found plastic in stool samples from eight donors, each from a different country (Poland, Russia, Japan, the Netherlands, the UK, Austria, Finland, and Italy). The poop donors volunteered their excrement for the sake of science, shipping their deposits in biohazard packaging for lab evaluation under the direction of the Environment Agency Austria. All submitted samples tested positive for a variety of plastics, from polyethylene (found in storage containers) to polypropylene (bottle caps) to PVC.

For each quarter-pound of the samples, 20 particles of microplastics were discovered ranging in size from 50 to 500 microns. A 50-micron particle is the smallest visible to the human eye.

Naturally, this means we have to be ingesting plastic in order to be excreting it. Scientists aren’t yet sure of the exact sources, though the food logs submitted by subjects might provide some clues. They drank from plastic bottles, ate from plastic containers, and ate fish that may have been exposed to plastic waste in polluted water.

The discovery is likely to encourage more wide-ranging studies involving a greater number of individuals about the possible health effects of having plastic particles in our digestive systems or bloodstreams. It may also be a call to reduce our dependence on plastics in general, and for food-related purposes specifically. In the meantime, gratitude is due the researchers and microscopists who went through a lot of crap to retrieve this data.

[h/t WIRED]

What Caused Pangea to Break Apart?

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.

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