Knowing that the distance from the outer part of Earth’s core to the top of the Gutenberg layer is the same as the diameter of the core, you can tell that convection within that space is virtually circular. It is one of those ideas becoming clear in a fraction of a second. After that we just need to work through the details to find out new things about Earth.
It is logical that convection that has been going on for billions of years has identical height and breadth. By adhering throughout to the same principle of identical height and breadth of convection rolls within every layer, and then a perfect horizontal path shaped by the Coriolis Effect, the interior of the Earth had been mapped.
Therefore it is possible to provide endless examples about wonders of the world.
It is easy to learn step by step. Step 1: In the upper most 120 km of the Earth, no convection takes place. The brittle layer of continents is thick, while the brittle layer of oceans is thinner. The ductile layer below works as a buffer, always adjusting the total thickness of a tectonic plate to 120 km.
So let us have a look at a drawing:
All the Eart’s surface is of that total thickness. The division line between brittle and ductile part is called the Moho discontinuity. The 120 km discontinuity divides the tectonic plates from the convective under-layer.
Step 2: Looking a bit further down it looks like this, with the two upper most layers of convection:
Step 3: Learn how these rolls extend over the whole Earth!
Step 4: Realize what the regular pattern of mantle convection rolls looks like 🙂
These rolls can be compered with the upper and lower currents of the ocean, and the upper and lower part of the troposphere of our atmosphere. Therefore it was possible to derive the exact shape and position of these rolls.