Look at this raft moving down a river. Look at this ball drifting along in a pool. Look at this Cheerio floating in milk. Now look at a map of the Earth. What if I were to tell you that those big areas of land were also floating along, just like the raft and the ball and the Cheerio? That the Earth under your feet is slowly moving, and you are moving with it? It's true! You may want to believe that the land is floating on top of the ocean you see, but it's a little different than that.
Hey, where did everybody go?
The land we stand on sits on top of a layer of melted rock. This lava is always moving, rising toward the crust when it gets hot and sinking toward the middle of the Earth when it cools down. This movement can act like little waves in a pool or the flow of a river. It can move the crust we stand on. Plate tectonics
is the theory that explains that the plates of land on the surface of the Earth are always moving. So why can you not feel it? Because they move very slowly. About as quickly as your fingernails grow. That's why we're not shouting WHEEEEEEEEE every day.
If you're going to wait for your fingernails to grow, don't hold your breath.
The crust of the Earth is not all connected like the shell on an unbroken egg. There are cracks. Take a boiled egg and give it a soft crack on the table. See the lines of the cracks in the shell now? That should give you some idea. The seven plates that make up our Earth are always moving. Sometimes they move over and under each other. When melted rock rises up, it will start to cool down and become solid, turning into hard rock. Ridges
are places under the ocean where new land pushes up to the bottom of the ocean. This works just like your fingernails, pushing out from under your skin. The Earth does not need to clip its land, though.
This egg cracks me up.
Instead of cutting all this new land off, like you would trim your fingernails, it just goes back under. Try to think about what it would be like if your nails grew out, and then went back into your fingers at the tip. In other places under the ocean, the plates are pushed down to make room for the new land. They slide under like one blanket being pulled on top of another. Trenches
are places where plates push under other plates and return to the insides of the Earth. They are like deep cuts into our planet. These cuts can let out a lot of heat. If you ever go on vacation to the bottom of the sea and are feeling a little cold, you may just want to find one of these cuts to warm up.
It's very hot down in the middle of the Earth, so the rock melts back into lava. This is the stuff our land floats on. Subduction
is the name for when old crust is pushed down into the middle of the Earth. It will stay melted until it rises back up again, cools, and gets pushed out as new land again. Just remember, when you are on the bottom of the sea, if you find yourself riding on a plate that's going under, do not panic. It's going really slowly, so simply swim away.
The ground beneath your feet is always moving. You drift along like a raft or a ball or a Cheerio. But you are not floating on water. Instead, you are floating on the melted rock that makes up the middle of the Earth. Lava rises up from the melted rock and cools into stuff you can stand on. This pushes other parts of the land back down into the middle to be melted and come up new at a later time. These plates we stand on may not be the fastest ride on Earth, but they sure beat holding onto something tight while the land you stand on cruises across the ocean.
Kids Geo. "Plate Tectonics" Kids Geo, 2012. <http://www.kidsgeo.com/geology-for-kids/0043-plate-tectonics.php
Science Spot. "Mountain Maker, Earth Shaker" PBS, 1998.