Why would life on Earth be impossible without the activity of bacteria?

Cyanobacteria release oxygen during photosynthesis. It was thanks to this group of organisms that molecular oxygen began to accumulate in the atmosphere about 2 billion years ago. As a result of the activity of these bacteria, the gas composition of the atmosphere changed and an ozone screen was formed. Bacteria play an important role in fixing atmospheric nitrogen. Bacteria play an important role in the biologically important cycles of substances on Earth, carrying out chemical transformations that are inaccessible to either plants or animals. Saprotrophic bacteria provide decomposition of complex organic substances, converting them into mineral compounds that can be absorbed by plants. As a result of the activity of saprotrophic bacteria, the Earth is cleared of the corpses of animals and plants. Thus, bacteria are also an important link in the cycle of substances in nature, as well as orderlies of our planet.