The tiny organisms had survived in the South Pacific seabed – in sediment that is poor in nutrients, but has enough oxygen to allow them to live.
Microbes are among the simplest organisms on Earth, and some would possibly live in excessive environments where a more evolved life bureaucracy survives.
After incubation through scientists, the microbes began to eat and multiply.
Studies conducted through the Japanese Marine Terrestrial Science and Technology Agency and published in the journal Nature Communications.
“When I found them, I was first sceptical whether the findings are from some mistake or a failure in the experiment,” lead author Yuki Morono told AFP.
“We now know that there is no age limit for [organisms] in the underwater biosphere.”
Professor and co-author Steven D’Hondt of the University of Rhode Island said the microbes came here from the oldest samples taken from the seabed.
“In the oldest sediment we’ve drilled, with the least amount of food, there are still living organisms, which can wake up, grow and multiply,” he said.
Previous studies have shown how bacteria can in complicated places, adding oxygen-free underwater vents around them.
Morono said the new discovery shows that some of the simplest living structures on Earth “don’t have the concept of lifespan.”