As you go to the outer core, the composition changes dramatically.
This outer core is now 85% iron, and
5% nickel, 5% oxygen, and 5% sulfur.
As you go into the inner most core, it's 94% iron and 6% nickel.
So you can see the increase in iron concentration,
nickel, as you get towards the center of the Earth, and also the reduction
in the amount of silicon and oxygen as you go into the center of the Earth.
So, let's talk about each of these different layers.
The Earth's crust is composed different plates, and there are two types of crust.
There's the oceanic crust which is primarily basalt, and
you have the continental crust which tends to be more granitic.
Currently, the crust is composed of these different plates, and
these plates move around on the earth due to the plate tectonics.
So we'll talk more about that in later lectures.
The mantle comprises 80% of the volume of the Earth.
It's mostly a rock called peridotite, which is mostly olivine and pyroxene,
and if we're lucky, we can see some pieces of the mantle that are occasionally
are brought to the surface of the Earth in what we call ophiolite sequences.
These are sections of ocean crust in upper mantle that have been uplifted
during plate tectonic processes, and exposed on the surface of the Earth.
As we go down towards the outer core, the outer core comprises one
sixth of the volume of the earth, but one third of its mass.
This is because of the much higher concentrations of iron.
As you get to the center of the Earth, the temperature is increasing, but
of course so is the pressure, and there is this zone,
where despite the increasing pressure, and the greater tendency to keep things solid,
the temperature is so high that the iron melts.
And that's exactly what happens here in the outer part of the core.
As you go to the inner core, despite the higher temperatures,
the pressure is so high, that the iron returns to a solid form.