Cooling of Earth's Core
Catherine Yoo - ESS Period 1
Sooo... What ARE Plate Tectonics?
Do Plates Move?
Heat? Mantle? Core? How does heat travel?
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.
Okay, so how does heat get to the surface?
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.
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.
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.