Many of you have already got an idea in your head of what you want your planet like, maybe what planets are around it. For everyone else, and those who are looking for inspiration everywhere, it may be good to decide how your planet formed. How it was formed can affect what minerals can be found on the planet, what the planet looks like, what the different climates are, what can grow on the planet, especially if Earth tries to colonize the planet, what animals could evolve on the planet, as well as where and how sentient species evolved and flourished.
A major question to ask here is if a thing of some sort created the planet for a reason or if the planet was a cosmic happening based on no actual plan. Remember, many species, judging by human cultures, will assume that everything happens for a reason and have a god of some sort in their infancy which they will may out grow by the time your story happens or they may avoid science by clinging to their “guiding hand”. (As a note, this blog is not a comment on human religion but an objective look at creating the best setting possible for your story. Many sci-fi species seem to go the way “educated” humans seem to go in saying science proves there is no god so faith in one is unnecessary.) Although religion will be a different topic, now would be a good time to decide if magic is in your world. If you wish magic to be powerful in your world it can change the natural order of things as I’ll explain things and as you go through this series you may want to keep magic in mind and how it changes the evolutionary process, same goes for if something created the planet. The Bible says that God created Earth with age. Humans were there on the sixth day the universe existed. That skips a lot of steps and means God plans really quick to form the center of the Earth, the moon, the sun, all the other stars with their possible systems, ecosystems, animals adapted to their habitat, and the complexities of humans in six days. (Unless He worked a lot of things out later which is contrary to traditional Christian belief.) Many polytheistic religions have gods creating Earth by dream or thoughts or something getting split into pieces and the planet forming from the pieces or from the act of the destruction (such as something died so something was born). If you wish the scientific reason for the planet to be a god or magic, keep that in mind while reading the rest of this series as gods are fickle in myths and often change the evolution of things.
The most accepted theory is nebular hypothesis which claims that the star comes first and particles surrounding the star eventually combine enough to create terrestrial planets, or planets like Earth that can theoretically contain life similar to ours. So why is planetary formation so important? It can create the building blocks for the minerals on the planet, which I will speak about next blog.