Determining the absolute "oldest cells on Earth" is impossible due to the nature of fossilization and the vastness of geological time. However, we can talk about the oldest evidence of cellular life, which comes from stromatolites.

Stromatolites are layered structures formed by the activity of microbial mats, primarily cyanobacteria. They are found in various parts of the world, and some of the oldest known stromatolites are located in Western Australia, dating back to around 3.5 billion years ago.

While these stromatolites don't contain intact cells, they represent evidence of microbial life that existed during that period. This makes them the oldest known evidence of cellular life on Earth, although there might have been other forms of life that haven't left any recognizable traces.

Therefore, we can't pinpoint the exact "oldest cells" but we can say that stromatolites provide the oldest known evidence of cellular life on Earth.