Surely, a lot of you are wondering why I'm starting at such a crude level. After all, if you're writing an alternate history or a real world saga, you already have the planet's physical form. This isn't true for all genres though. People writing about far-off places and beings may have one, ten, a hundred, or hundreds of worlds to deal with. I don't want to leave out those who may need to build their own planet from scratch.
On the other hand, a lot of you don't need some strange new world to work with. You're maybe writing a historical or current piece set in the Earth we all know and love. All of the techniques and considerations we will use throughout our world-building journey are useful somewhere. Even if your world already exists, you'll learn about all of the underpinnings it's worth studying. For example, every culture has its spoken and unspoken rules. What are they? Where did they come from? When did they appear, and in what region? Once you see how to build these things from the ground up, it will be easier to look backwards and study reality.
Laying the Foundation
So, here we have it. A ball of swirling magma. Right now, it's just a collection of liquid rock with no real form. We could actually start with other kinds of planets, but I'm going to keep us Earthlike on this front at least.
On top of magma here on Earth are the tectonic plates. These are big masses of "earth" that float on top of the magma and support everything else. They form as the magma's surface cools and shifts and cracks during planet formation. Whether it's a mountain or the bottom of the ocean, it's resting on top of this magma. These huge slabs of solid material are broken into pieces called plates. Believe it or not, these objects float around and move and shift over time. For example, once upon a time our whole planet had one large continent called Pangea. It split apart and drifted and moved over the aeons into what we have today. Earth has about twelve of these plates.
