Presumably, that would put them among the oldest known life forms:
A team of geologists has just discovered tiny remnants of prokaryotic and algal life – trapped inside crystals of halite dating back to 830 million years ago…
Using a core sample from the Browne Formation extracted by the Geological Survey of Western Australia in 1997, Schreder-Gomes and her colleagues were able to conduct investigations of unaltered Neoproterozoic halite using nothing but non-invasive optical methods. This left the halite intact; which, importantly, means that anything inside had to have been trapped at the time the crystals formed…Michelle Starr, “Potentially Alive 830-Million-Year-Old Organisms Found Trapped in Ancient Rock” at ScienceAlert (May 16, 2022)
The researchers think that some of the remnants may still be alive. “And living prokaryotes have been extracted from halite dating back 250 million years; why not 830 million?”
We shall see. The implications for finding fossil remnants of life on Mars are addressed in the article.
The researchers acknowledge that survival of microorganisms over geological timescales is “not fully understood.”
The paper is open access.
You may also wish to read: Researchers: Eukaryotes got started from a merger between bacteria and archaea, without oxygen. On the whole, it might be easier to conclude that the timing is somewhat off than that complex life started without oxygen. But symbiosis is an intriguing theory nonetheless.