Albert Barnes Commentary Psalms 104:30

"Thou sendest forth thy Spirit, they are created; And thou renewest the face of the ground." — Psalms 104:30 (ASV)

Thou sendest forth thy spirit, they are created - That is, new generations are created in their place, or spring up as if they were created directly by God. They derive their being from him just as truly as did those that were first formed by his hand, and the work of creation is constantly going on.

And thou renewest the face of the earth - The earth is not allowed to become desolate. Though one generation passes away, yet a new one is made in its place, and the face of the earth constantly takes on the appearance of freshness and newness.