The first cities were built by bacteria, layer by layer, over billions of years.

Stromatolites are not just fossils—they are living architecture. These layered structures, some over 3.5 billion years old, were built by cyanobacteria that trapped sediment and minerals in their sticky biofilms. Each layer represents thousands of years of microbial activity, creating the first "cities" on Earth. These ancient architects not only built the first complex structures but also transformed the planet by producing oxygen through photosynthesis. The Great Oxidation Event, which began around 2.4 billion years ago, was largely driven by these microscopic builders. Today, living stromatolites can still be found in Shark Bay, Western Australia, where conditions remain similar to the ancient world. They are living fossils, direct descendants of the organisms that first made Earth habitable for complex life. Each stromatolite is a time capsule, preserving the story of how life learned to build, cooperate, and transform the world around it.