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  • Hi this is Emily from MinuteEarth.

  • A little while back, Henry made this great MinutePhysics video about how the weird symmetry

  • of light and shadows on a landscape can make it really hard for your brain to tell which

  • features are popping out and which ones are dented in, especially if you're not sure

  • where the light is coming from.

  • This re-ignited an old debate we had here at MinuteEarth, about THIS photo of the surface

  • of Mars.

  • That sinuous pattern on the landscape is an ancient stream channelwhich is cool because

  • it means that liquid water used to flow on Marsbut that crater above it has a shadow

  • in the top left, which means the light in the image must be coming from the top left,

  • which seems to suggest that the stream channel is actually sticking up above the surrounding

  • landscape.

  • But...that can't be right, right?

  • I mean, river channels should obviously be valleys, since they've been carved into

  • the ground.

  • This seemed like such a basic fact to me that, even when everyone else on my team said they

  • saw this as a ridge, my brain kept telling me it was a valley.

  • It turns out that, not only was my brain lying, but this stream channel is an example of a

  • weird geological process that essentially turns landscapes inside out, creating inverted

  • relief.

  • If you live in a cold climate, you may have actually seen something like this happen with

  • compacted footprints in the snowas the sun melts the fluffier snow around them, they

  • can end up sticking out, like this.

  • The same thing can happen to a river valley.

  • For instance, say you've got a stream running through a desert.

  • Sometimes there is so little rain that the stream dries up.

  • As it does, some groundwater is actually drawn upward by capillary action, and as it rises

  • and evaporates, dissolved minerals in it are left behind and precipitate out, coating the

  • sediments in the riverbed and cementing them together.

  • As the stream flows and dries up over and over again, more and more cement accumulates,

  • making the riverbed harder and more resistant to erosion than the surrounding rock.

  • Over the eons, wind erodes that softer rock, turning the channel into an inverted version

  • of its former self.

  • We can't know exactly how this Martian riverbed got turned inside out without getting down

  • on the ground and digging around a little, but we can make some good guesses by studying

  • inverted relief on our home planet.

  • You can even find your own examples on Google Earth; just be warned that trying to figure

  • out what's rightside-up and upside-down could turn your brain inside-out.

  • Hi, this is Ever and I illustrated this video.

  • Lots of you have asked how I create animated effects like this one.

  • It's not magic; in fact, it's pretty easy to do if you've got the right tools - and

  • the right teacher.

  • I was never one for formal school, but the online classes from experts at Skillshare

  • are perfect if you're a self-directed learner like me.

  • You can try out skillshare's impressive library of 17,000 how-to classes on everything

  • from video editing to T-shirt design.

  • The first 200 people to click the link in the description will get a 2 month free trial.

Hi this is Emily from MinuteEarth.

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B1 中級 美國腔

火星河?(UPSIDE-DOWN Rivers On Mars?! (Response to MinutePhysics))

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    joey joey 發佈於 2021 年 04 月 30 日
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