In the stage of bipolar ecosystem, there are no animals, and the bipolar ecosystem consists of producers and decomposers.
In the bipolar ecosystem, because the consumption of organic matter in the "original soup" exceeds its natural output day by day, that is, the operation mechanism of material transformation is unbalanced, so it is impossible to maintain a single heterotrophs. About 2.5 ~ 3 billion years ago, due to the constant variation and evolution of anaerobic heterotrophic prokaryotes, cyanobacteria with chlorophyll finally appeared. They can use light energy to release oxygen for photosynthesis and make nutrients from inorganic substances, so they are aerobic autotrophs. The birth of this autotrophic organism made the early ecosystem have two links, namely, synthesis and decomposition, thus forming a complete bipolar ecosystem. Autotrophic cyanobacteria are synthesizers, that is, "producers" in the ecosystem, and heterotrophic bacteria are "decomposers". They obtain organic nutrients from cyanobacteria, decompose them into inorganic substances, and then supply them to "producers".