What life existed a billion years ago?

A billion years ago, during the Proterozoic Eon, life on Earth was primarily unicellular and microscopic. Organisms such as bacteria and archaea dominated, with some early eukaryotic cells appearing. These life forms thrived in oceans, and stromatolites, formed by cyanobacteria, were prominent in shallow marine environments. Multicellular life was still largely absent, and the atmosphere had low levels of oxygen compared to today.