earthworms create tunnels in soil & tunnels in soil loosen that soil ->  earthworm can help loosen the soil by creating tunnels  earthworm can help loosen the soil by creating tunnels & the looseness of soil increases the amount of oxygen in that soil ->  earthworm creating tunnes can increase the amount of oxygen in the soil  earthworm creating tunnes can increase the amount of oxygen in the soil & trees takes in oxygen through roots close to the surface of the ground -> more oxygen is available for tree roots