700 million years ago. Earliest multicellular fossils.
Perhaps the oldest and most spectacular fossils of multicellular organisms are those Shuhai Xiao found in the quarries of Doushantuo, Weng’an, in southern China.
They are a series of mysterious spherical fossils that could be remnants of the earliest multicellular animals or embryos of an ancient organism. They are dated around 700 million years old. They are fossilized organic material trapped in sediments, which prevented its decomposition and allowed the replacement of the original pore spaces with minerals over time.
These fossils are of great value since they offer some evidence about how the transition from unicellular organisms to things like plants and animals might have happened in evolutionary history.
One of the simplest theories that try to explain the origin of multicellular organisms suggests that it ocurred when microbes developed new ways to eat other microbes or to avoid being eaten.