About 1.3 billion years ago, after oxygen began reshaping Earth, life settled into several major branches. The great ecological cast was taking shape. One branch stayed bacterial and continued running the planet’s chemistry. Another branch became the eukaryotes: larger, more complex cells that eventually gave rise to plants, fungi, animals, algae, and many single-celled protists.

From there, the story becomes familiar. The plant branch became mosses, ferns, trees, grasses, flowers, and crops. The fungal branch became molds, yeasts, mushrooms, and vast underground networks. The animal branch became sponges, worms, fish, insects, reptiles, birds, mammals, and eventually us.

Meanwhile, bacteria kept doing the work almost no one notices. Cyanobacteria made oxygen. Proteobacteria recycled chemicals and helped give rise to mitochondria. Actinobacteria built soils and produced natural compounds. Firmicutes became tough survivors and gut companions. Bacteroidetes became expert decomposers. Other bacterial branches moved through mud, cycled nitrogen, broke down waste, and kept ecosystems alive.

The simple story is this: complex life branched into the visible world of plants, fungi, and animals, while bacteria and archaea remained the invisible workforce beneath it all.

Life did not replace its earliest tricks. It kept them. Bacteria still recycle the world. Archaea still endure strange environments. Cyanobacteria still harvest sunlight. Viruses and mobile genes still reshape evolution from the shadows. The ancient world is not gone; it is under our feet, in our oceans, and inside us.