First organism large enough to be seen by human eye (if there were humans then)

In the four billion years of the evolution of life, what was the first organism large enough to be seen by the naked human eye (if there had been human beings then,)
If the answer is something like coral, what is the first not an accumulation…

If you allow for a colonial/collective organism, stromatolites. If a single multicellular organism, possibly something ancestral to one of these weirdos.

Impossible to know, since the first organisms large enough to see would have been soft bodied and would not have left fossils. However, the first macroscopic fossils of single organisms seem to date to about 2.1 billion years ago. However, they are just smudges of carbon that don’t really reveal what kind of organisms made them.

Stromatolites go back about 3.7 billion years ago, but these represent mats of cyanobacteria (blue-green “algae”) and not single organisms.

The first complex multicellular life we know of for certain is the Ediacara fauna. 600 Ma.

David Attenborough made a documentary series called First Life that you might gain some knowledge from.

Obligatory Far Side reference: