Construct an argument for how earth's interior layers may have formed, and how the layers contribute to earth's processes.

In the beginning, the earth was a part of the solar nebula, which was a huge gas and dust cloud.  Earth was formed by a process called accretion, which basically is the accumulation of bits and pieces of dust and gas together.  Earth took about ten to twenty million years to form, then was relatively molten with lots of volcanic activity, due to all the collisions that were taking place. Due to the fact everything was molten, the denser, heavier elements, such as iron, settled to the center, while the lighter, less dense elements stayed in the outer layers.  This would explain why the earth has an iron core, then a less dense molten mantle, and then a lighter, least dense rigid outer crust.  The iron core is divided into an outer core, which is liquid, and an inner core, which is solid.  This two-part core tandem is responsible for generating earth's magnetic field, which protects the earth from harmful particles in the sun's solar wind.  The outer crust is fractured, or broken, into large and small pieces called tectonic plates.  Part of the processes of the earth involve these plates pushing into each other, pulling apart from each other, or sliding past each other.  All these processes produce volcanic and seismographic events on a recurring and regular basis.  The crust has new crustal material added and old crustal material subducted into the mantle, where it is melted down and recycled again.  All these processes result in the earth producing volcanoes and earthquakes as a general rule.