Using Rhenium-Osmium dating, scientists have dated the oldest known sexually reproducing organism, and the oldest multicellular organism that used photosynthesis - a red algae called Bangiomorpha pubescens - to between 1.03 billion and 1.06 billion years old.

See the source article by following the link below:
Using Rhenium-Osmium dating, scientists have dated the oldest known sexually reproducing organism, and the oldest multicellular organism that used photosynthesis - a red algae called Bangiomorpha pubescens - to between 1.03 billion and 1.06 billion years old.