How does life on earth depend on photosynthesis?

Humans and many mammals rely on plants to survive. The plants are eaten by insects and insects and small mammals. Insects are eaten by small mammals such as frogs and small mammals are eaten by bigger animal such as a lion. The food chain basically. So if photosynthesis no longer occurs the plants would die out and many mammals would die as well. Cows, pigs and chicken (many of our livestock) rely on plants so our livestock would die out and we would also die