His last spike made a new life form that doesn’t dwell in water. To accomplish this he used his third trident to swirl the sea to create a sea storm and out came a new form of life, humans. Since humans were land creatures he took some water away and created land.
Out sprang trees, grass, and mountains, a new wonder of the Earth. Before humans could be set free the sea animals he created gave them life and survival. After a human could be on their own they would learn properties of an animal because they were raised by animals and Poseidon himself.
Poseidon was the mother nature of the sea. He controlled whether it rained, snowed, or hailed. He created natural disasters like hurricanes, tornadoes, and tsunamis. He determined the weather by how his creatures treated him. If they weren’t being respectful to their master, their consequence would be to deal with the terrible weather conditions which were extreme.