How do earthworms affect the soil?
They increase the amount of oxygen, water, and other nutrients.
Earthworms live in the soil and break down organic matter such as grass, leaves, etc. They break it all down into things plants can use, such as nutrients.
They decompose the matter in the soil by eating it, digesting it, and passing it out in the form of castings. When they are eating, they leave a trail of fertilization for the plants.