2.1 billion years ago. Earliest eukaryotic fossil.
The earliest multicellular eukaryote known fossils are Grypania spiralis. They were found in 1992 embedded in rocks dated 2.1 billion years old, from an open pit iron mine, SE of the town of Ishpeming and NW of Palmer, in Michigan. They consist of a collection of rocks which show a series of coiled tubes.
There is debate as to whether they are eukaryotic algae or complex cyanobacteria. Given their size (longer than 1 centimeter), they are most probably filaments of red algae, which are eukaryotic organisms.
Eukaryotes are those organisms containing membrane-bound complex structures. Their cells differ from prokaryotic ones by having a nucleus containing genetic material.