Cooling of Earth's Core

Catherine Yoo - ESS Period 1

Sooo... What ARE Plate Tectonics?

Plate tectonics is the theory that Earth's outer shell is divided into several plates that glide over the mantle, the inner layer above the core. The plates are like a hard shell, and this strong outer layer is called the lithosphere.
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Do Plates Move?

Yes, yes they do. Plates move as a result of high temperatures inside Earth. But before that...

Heat? Mantle? Core? How does heat travel?

We know that heat travels from a warm object to a cooler object, so heat inside Earth is somehow getting to the surface. Evidence of this is volcanoes, but this measurement of heat is made near the surface. Heat deep inside of Earth is observed using computer simulations, which compares seismic and heat flow data to show the temperature variations in the core.


So the core is the hottest part inside Earth, and the heat is resulting partly from leftover heat when the Earth was created, partly heat released by the freezing of liquid iron in the outer core onto the solid inner core, and partly heat from radioactive elements (like uranium and potassium). The core can heat the mantle because hot rocks near the bottom of the mantle are a tad less dense than the cooler rocks on top. Buoyancy pushes the hot rocks up, and while rocks are solid, pressures and heat in the mantle are so intense that they deform (think about wax, candles). As hot rock rises, cooler rock replaces it and goes down next to the core, become heating, rising, and starting the process all over again. The zone where rock is soft is called the asthenosphere.

Recognize it?

This is a process you see in your everyday life, right in your home. It's in your kitchen! (... Unless you don't cook, I guess) It's called convection. When you heat a pan of water to boil, hot water from the bottom of the pan rises up the sides, flows to the center, and sinks to the bottom again.
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Okay, so how does heat get to the surface?

Rock near the Earth's surface, the lithosphere, is cold so it can't flow like mantle rock. That's when conduction comes into play.


Imagine an iron pan over a fire on the stove. The part over the flame gets hot first, and then the handle gets hot. But the handle isn't over the flame! There was no movement of hot material in the pan (the metal definitely didn't flow). This process is called conduction, when the heat, vibrations of atoms in the solid pan, moves as a result of fast moving hot atoms bouncing off slow moving cool atoms. This causes slow atoms to move faster and heat up.


So at the top of the asthenosphere, hot rock flows along the bottom of the lithosphere, transferring heat to the cold rocks by conduction.

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Another way

Another way heat can get to the surface is -- it was mentioned earlier -- did you guess it? Volcanoes! Lava flowing through cracks brings heat to the surface, and are what we call volcanoes.
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Finally!

Okay, okay, now that I've explained everything, I can finally tell you why all this heat traveling is related to plates tectonics.


The movement of heat by convection in the asthenosphere causes the rock of the mantle to slowly move in huge streams. The solid, brittle rock of the lithosphere is resting directly on top of the solid, soft rock of the asthenosphere. As the rock of the asthenosphere moves in different directions, it carries parts of the lithosphere along with it. The lithospheric rock can't stretch, so it breaks into pieces -- forming the plates.

Cooling down

So heat is constantly traveling out of the core, technically (tectonic-ally haha. Oh I'll stop) the core has been cooling down. Very slightly, but yes, cooling down. Well, since heat also moves water to the surface, we'll probably have no more water. Dried up, just like Mars is right now (scientists believe that Mars had large bodies of water, before it dried up). Plate tectonics won't work properly, because there won't be any more convection, which requires heat.


But forget about plate tectonics. If the core cools down very quickly (which is not happening, the cooling is very, very, gradual) the magnetic field around Earth will disappear. And that magnetic field is important! Without it, we'll all be fried by the Sun.

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