Where do you go to get fresh bread? The bakery.
Where do you go to get a fresh piece of paper? The paper factory.
Okay, now where do you go to get new
land? What? New land? Don't we just have the land around us that's neither old nor new? It just . . .
is? Just like a bakery bakes bread and a factory cuts new paper, our planet makes new land. But we can't go around the corner to the store to get it. Grab your scuba suit. We're diving to the bottom of the ocean.
Look everybody, new land this way!
U.S. Navy photo by Mass Communication Specialist 1st Class JoshTreadwell, Public domain, via Wikimedia Commons
We splash into the waves, diving deeper and deeper while bubbles rise above us. While we're sinking down, there's an important word you should know.
Create means to bring something new into the world. It's a fancy word for "make." But
making a bed by tucking in the sheets and
creating a bed by building it from wood are two very different things. The Earth creates new land, but it must make it out of something. Just like bread is made from sugar, flour, and eggs and paper is made from trees, new land is made from melted rock from the middle of the Earth. No wonder the water's starting to get warm.
Bread so fresh you can smell it. Well maybe not at the bottom of the ocean.
ProjectManhattan, CC0, via Wikimedia Commons
While we keep sinking, keep your eyes peeled for the land factory. But wait, what does it look like? And how do we know where it is? We dove down into the Atlantic ocean, because right in the middle is where two of Earth's plates meet. When you think about Earth's plates, you might think of puzzle pieces that fit together. And you'd be right . . . kind of. These puzzle pieces are always on the move. The plates we're dropping toward are moving away from each other. A
divergent boundary is a place where two of Earth's plates are moving apart. This is where we'll find our land factory.
If you're going to build land, it's going to take a lot of puzzle pieces.
There's the sea floor! And there are . . . mountains?! What are
they doing here? These mountains are spills from the land factory. Have you ever baked bread? It can get messy. When you are stirring it all up in a bowl, some dough might splash out. Flour gets everywhere. As the melted rock come out of the middle of the Earth, it cools in the cold ocean water and then build up to become a whole mountain range!
Mid-ocean ridges are under water mountains that spring up where two plates are moving apart. If you never cleaned up your kitchen floor, they might start getting some mountain ranges too. Stinky mountain ranges.
So if the mountains are what the factory has spilled, where is the factory? At the foot of the mountains is a place where the Earth's crust is very weak. It is at this point that the melted rock can escape from the middle of the Earth and push up into the ocean.
Sea floor spreading is when new land pushes up from the middle of the Earth and pushes apart the land under the ocean. Because it's so cold at the bottom of the ocean, it freezes into solid rock! It's like a conveyor belt in a factory, bringing new stuff up and then eventually, sinking back down again. Aww, baby land. Isn't it cute? No?
We did it! We found the land factory! By diving into the ocean where two plates meet and then sinking down until we found the mountain range, we can find where the sea floor spreads and new land moves out like a conveyor belt at the grocery store. Land has to come from somewhere, and we just found where it's made. Now what? We can't eat this land like a piece of bread. We can't draw on it like a piece of paper. We can't even bring it back to show your teacher. I guess we'll just . . . stand on it. Yay.
References:Kids Fun Science. "Divergent Boundaries" Kids Fun Science, 2013. <
http://www.kids-fun-science.com/divergent-boundary.html>
The Encyclopedia of Earth. "Mid-ocean Ridges" Eoearth, 2010. <
http://www.eoearth.org/view/article/164696/>
Our Changing Continent. "Magnetic Striping" USGS, 2012. <
http://platetectonics.pwnet.org/story_tectonics/theory/magnetic_striping.htm>