Earth's Core Hottest Layer
Date: Spring 2011
Why is the inner core the hottest layer? How is that possible?
There are two factors causing the center of the Earth hotter than various
layers of the Earth's. First, the more dense is the layer. The denser
layer, the hotter it will be. In addition, the source of the heating is due
to heat produced by nuclear decay. These substances tend to be more dense
than lower dense substances. So the source of heat (temperature) is higher,
the greater will be the temperature.
Having said all that, the reasons are rather more complicated in the "real"
Earth. If the inner layers were less dense they would rise (bubble) to the
"surface" leaving the inner layers more dense and thus hotter layers.
The inner core of the Earth is the hottest because of the enormous
amount of pressure.
You can try an experiment at home to prove that pressure will raise
the temperature of an object. You'll probably want to wear gloves
so that you do not hurt your fingers and have a parent help you
out. Take a very thin wire, or possibly some dental floss. Next,
get an ice cube out and then try pull the wire through the ice
cube. Putting the ice cube on the edge of a counter might work best
so that you have room on the sides of the ice cube to be able to
pull down. What you should see is that putting the pressure on the
ice cube will melt the ice around where the wire is. If you keep at
this, you can eventually pull the wire into the middle of the ice
cube and have the section above the wire refreeze so that the wire
is going right through the middle of the ice cube!
Now, think about how much pressure there must be in the core of the
Earth given the weight of all of the dirt and rock on top of
it. The center of the Earth is made of iron and it is so hot, in
fact, that the iron is liquid!
The temperature of the inner core of the Earth is believed to be due to
radioactive decay of radioactive elements. Plus the gravitational attraction
of the heavier, that is more dense, elements. So the source of heat is the
center of Earth (more or less). These sources combined, are much hotter
than the surrounding upper, and less dense, layers of Earth's makeup.
That is why volcanoes give us a glimpse of what is "going on" deep in
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Update: June 2012