1 billion years ago?
For the first time, life was not just made up of single cells. Now cells were teaming up to form larger organisms with things like mouths, limbs and sense organs. It’s hard to say when this happened: there are fossils of large organisms dating back 2.1 billion years, but these may simply have been colonies of bacteria. Different groups of organisms probably evolved multicellularity independently, with plants managing it before animals.
See other: History of Life