字幕列表 影片播放 列印英文字幕 This video is sponsored by NordVPN. Hi, this is Emily from MinuteEarth. From the tip of Mt. Everest to the bottom of the Mariana trench, elevations on Earth span over 65000 feet. But we all know that those extreme elevations are super rare, and that the vast majority of our planet's surface falls somewhere in the middle range So it seems like, if you added up the points at the very top, and then a little lower, and all the way down to the bottom you'd end up with something like this – a simple, normal distribution, with very little area at the top and bottom, and a big hump in the middle near sea level. And if we were talking about our sister planet Venus, we'd be right – this is what the elevation-distribution curve looks like for Venus. But Earth's elevation is distributed like this: it has TWO humps – so, very few points very high and very low, but a lot of points around sea level and then, again, a lot of points several thousands feet below. And if you took all of those points and arranged them from lowest to highest, you could see that Earth's surface has two sort of levels to it. The main reason is that Earth's outer layer, the crust, is made up of two different materials: it's all rock, but the rock that makes up the seafloor is denser than the rock that makes up the continents. And this density difference has major consequences, because ocean floors and continents don't just sit there – together with the rocky mantle below them, they're broken up into big plates that ride around on convection currents flowing deep inside of Earth. And when two plates collide, the outcome is pretty much determined by density: oceanic plates are denser than continental ones – in fact, they're so dense that when the two plates collide, the oceanic one sinks back down into the planet. On the other hand, when two continents collide, neither is dense enough to go down, so instead they both go up, creating mountain ranges and thickening up the continental crust. As a result, the continental crust is, on average, about four times thicker than the ocean crust, so its average elevation is much higher than the average elevation of the ocean floor, which explains this weird, double-humped elevation-distribution curve. And actually, if our planet's surface was more like Venus's, with it's so-called normal distribution, only about 5% of it – an area a little smaller than Africa – would be above sea level, leaving not much space for landlubbers like us. Just one more reason to be glad there's nothing normal about Earth. Have you ever had that experience where some of your favorite creators get together and make an awesome new show that you can't watch because of geoblocking? Or are you someone who uses the internet AND values your privacy? Then you may want to know about this video's sponsor, NordVPN. Nord encrypts your data and then routes it through thousands of servers in 61 countries around the world, keeping your browsing safe from the prying eyes of thieves, internet service providers, and even governments, all without logging any of your data itself. To get started with NordVPN and get 77% off a 3-year plan, go to NordVPN.com/minuteearth and use the code MINUTEEARTH at checkout. That's NordVPN.com/minuteearth.