Oxygen entered the Earth's atmosphere after the appearance of the Great Oxidation Event (Great Oxygenation Event). The Great Oxidation is the first mass extinction on Earth.
The Great Oxidation lasted 2.4 to 2.0 billion years ago.
Oxygen appeared on Earth thanks to cyanobacteria using photosynthesis.
Ftsz, mreb, and cres ,proteins regulate the shape and structure of bacterial prokaryotic cells. These proteins are homologous to the Cytoskeleton in eukaryotes. Homologous meaning they have the same evolutionary origin but not necessarily having the same function. Cytoskeleton forms a framework for the movement of organelles around the cytoplasm, most organelles are attached to the cytoskeleton.
Bees are endangered because of environmental stress. Environmental stress may come from pollution, exposure to lethal amounts of pesticides, and due to scarcity of pollen.